Search

On-surface photocatalytic degradation of Methylene Blue was conducted on a paper surface and the process continuously monitored using paper spray ionization mass spectrometry. Firstly, the photocatalyst (TiO2) was immobilized on the paper surface, which was later cut in a triangle shape. A small amount of an aqueous solution of the dye Methylene Blue, used as a prototype target, was then added to the paper and the system exposed to UV-C radiation. Control experiments (photolysis) were also conducted, in which the paper surface contained no TiO2. All the processes were analyzed by paper spray mass spectrometry using lidocaine as internal standard, which was added to the paper just before analyzes. By measuring the intensities of the ions of m/z 284 (cationic Methylene Blue) and m/z 235 (protonated lidocaine) the performance of both processes (on-surface photocatalysis and photolysis) were compared. Photocatalysis showed a remarkable superior performance to degrade Methylene Blue in comparison to photolysis. The absorption of UV-C radiation by TiO2 probably generated reactive species on the paper surface that caused faster dye degradation. In conclusion, paper spray ionization mass spectrometry proved to be a convenient platform where on-surface reactions can be promptly investigated.

Chemical and spectroscopic characterization of the mononuclear photosensitizers [(DPEPhos)Cu(I)(MPyrT)]0/+ (CuL, CuLH) and their dinuclear analogues (Cu2L’, Cu2L'H2 ), backed by (TD)DFT and high‐level GW‐Bethe‐Salpeter equation calculations, exemplifies the complex influence of charge, nuclearity and structural flexibility on UV‐induced photophysical pathways. Ultrafast transient absorption and step‐scan FTIR spectroscopy reveal flattening distortion in the triplet state of CuLH as controlled by charge, which also appears to have a large impact on the symmetry of the long‐lived triplet states in Cu2L’ and Cu2L'H2 . Time‐resolved luminescence spectroscopy (solid state), supported by transient photodissociation spectroscopy (gas phase), confirm a lifetime of some tens of μs for the respective triplet states, as well as the energetics of thermally activated delayed luminescence, both being essential parameters for application of these materials based on earth‐abundant copper in photocatalysis and luminescent devices., The comprehensive results on two mononuclear pyridyl‐triazole/DPEPhos based Cu(I) complexes and its extension to their two dinuclear analogues paves the road to addressing the complex coupling of the respective monomeric units, involving various physical and chemical properties as charge, (electronic) structure and (long‐lived) excited state properties, relevant for applications.

We developed three bathochromic, green‐light activatable, photolabile protecting groups based on a nitrodibenzofuran (NDBF) core with D‐π‐A push–pull structures. Variation of donor substituents (D) at the favored ring position enabled us to observe their impact on the photolysis quantum yields. Comparing our new azetidinyl‐NDBF (Az‐NDBF) photolabile protecting group with our earlier published DMA‐NDBF, we obtained insight into its excitation‐specific photochemistry. While the “two‐photon‐only” cage DMA‐NDBF was inert against one‐photon excitation (1PE) in the visible spectral range, we were able to efficiently release glutamic acid from azetidinyl‐NDBF with irradiation at 420 and 530 nm. Thus, a minimal change (a cyclization adding only one carbon atom) resulted in a drastically changed photochemical behavior, which enables photolysis in the green part of the spectrum., What a difference one atom makes: Azetidine (az) and dimethylamino (DMA) donor moieties differ only by one carbon atom in their molecular formula, but in the present study we observed huge differences in their impact on the photochemistry of D‐π‐A caging groups. Restriction of the degrees of movement freedom—due to the four‐membered ring—leads to a photocage that can be used within the “green gap” for the release of biologically relevant leaving groups (e.g., glutamic acid).

Tetraacylgermanes are known as highly efficient photoinitiators. Herein, the synthesis of mixed tetraacylgermanes 4 a–c and 6 a–e with a nonsymmetric substitution pattern is presented. Germenolates are crucial intermediates of these new synthetic protocols. The synthesized compounds show increased solubility compared with symmetrically substituted tetraacylgermanes 1 a–d. Moreover, these mixed derivatives reveal broadened n–π* absorption bands, which enhance their photoactivity. Higher absorption of these new compounds at wavelengths above 450 nm causes efficient photobleaching when using an LED emitting at 470 nm. The quantum yields are in the range of 0.15–0.57, depending on the nature of the aroyl substituents. On the basis of these properties, mixed‐functionalized tetraacylgermanes serve as ideal photoinitiators in various applications, especially in those requiring high penetration depth. The synthesized compounds were characterized by elemental analysis, IR spectroscopy, NMR and CIDNP spectroscopy, UV/Vis spectroscopy, photolysis experiments, and X‐ray crystallography. The CIDNP data suggest that the germyl radicals generated from the new tetraacylgermanes preferentially add to the tail of the monomer butyl acrylate. In the case of 6 a–e only the mesitoyl groups are cleaved off, whereas for 4 a–c both the mesitoyl and the aroyl group are subject to α‐cleavage., Just mix it! Mixed‐functionalized tetraacylgermanes were synthesized by two innovative pathways. These new derivatives outperform the state‐of‐the‐art germanium based photoinitiators in terms of both solubility and absorption properties.

Heteronuclear calcium–iron carbonyl cation complexes in the form of [CaFe(CO)n]+ (n=5–12) are produced in the gas phase. Infrared photodissociation spectroscopy in conjunction with quantum chemical calculations confirm that the n=10 complex is the coordination saturated ion where a Fe(CO)4 fragment is bonded with a Ca(CO)6 fragment through two side‐on bridging carbonyl ligands. Bonding analysis indicates that it is best described by the bonding interactions between a [Ca(CO)6]2+ dication and an [Fe(CO)4]− anion forming a Fe→Ca d−d dative bond in the [(CO)6Ca–Fe(CO)4]+ structure, which enriches the pool of experimentally observed complexes of calcium that mimic transition metal compounds. The molecule is the first example of a heteronuclear carbonyl complex featuring a d−d bond between calcium and a transition metal., The [CaFe(CO)10]+ cation is characterized to be a coordination saturated ion where a Fe(CO)4 fragment is bonded with a Ca(CO)6 moiety through two side‐on bridging carbonyl ligands. The complex is best described by the bonding interactions between a [Ca(CO)6]2+ dication and an [Fe(CO)4]− anion forming a Fe−Ca d−d dative bond that is enhanced by the attraction between Ca and the bridging CO ligands.

The synthesis and structural determination of four tungsten alkyne complexes coordinated by the bio-inspired S,N-donor ligand 2-(4',4'-dimethyloxazoline-2'-yl)thiophenolate (S-Phoz) is presented. A previously established protocol that involved the reaction of the respective alkyne with the bis-carbonyl precursor [W(CO)2 (S-Phoz)2 ] was used for the complexes [W(CO)(C2 R2 )(S-Phoz)2 ] (R=H, 1 a; Me, 1 b; Ph, 1 c). Oxidation with pyridine-N-oxide gave the corresponding W-oxo species [WO(C2 R2 )(S-Phoz)2 ] (R=H, 2 a; Me, 2 b; Ph, 2 c). All W-oxo-alkyne complexes (2 a, b, c) were found to be capable of alkyne release upon light irradiation to afford five-coordinate [WO(S-Phoz)2 ] (3). The photoinduced release of the alkyne ligand was studied in detail by in situ 1 H NMR measurements, which revealed correlation of the photodissociation rate constant (2 b>2 a>2 c) with the elongation of the alkyne C≡C bond in the molecular structures. Oxidation of [WO(S-Phoz)2 ] (3) with pyridine-N-oxide yielded [WO2 (S-Phoz)2 ] (4), which shows highly fluxional behavior in solution. Variable-temperature 1 H NMR spectroscopy revealed three isomeric forms with respect to the ligand arrangement versus each other. Furthermore, compound 4 rearranges to tetranuclear oxo compound [W4 O4 (μ-O)6 (S-Phoz)4 ] (5) and dinuclear [{WO(μ-O)(S-Phoz)}2 ] (6) over time. The latter two were identified by single-crystal X-ray diffraction analyses.

In the terrestrial dipolar magnetic field, magnetic circular dichroism (MCD) of UV sunlight by paramagnetic O(2) in an Archean atmosphere (mostly CO(2) and N(2)) results in circular polarization anisotropy (~ 10(−10)). This is used to calculate enantiomeric excess (EE~10(−13)) of glyceraldehyde (3-carbon sugar) with a model that includes racemic production and asymmetric photolysis of its enantiomers. The sign and magnitude of enantiomeric excess (EE) vary with the Earth’s latitude. Unlike random noise fluctuation in spontaneous mirror symmetry breaking (SMSB) models, the sign of EE is deterministic and constant over large areas of prebiotic Earth. The magnitude is several orders greater than the mean amplitude of stochastically fluctuating EE. MCD could provide the initial EE for growth of homochirality by asymmetric autocatalysis.

Diamondoid cations are reactive intermediates in their functionalization reactions in polar solution. Hydration is predicted to strongly activate their C−H bonds in initial proton abstraction reactions. To study the effects of microhydration on the properties of diamondoid cations, we characterize herein the prototypical monohydrated adamantane cation (C10H16 +–H2O, Ad+–W) in its ground electronic state by infrared photodissociation spectroscopy in the CH and OH stretch ranges and dispersion‐corrected density functional theory (DFT) calculations. The water (W) ligand binds to the acidic CH group of Jahn–Teller distorted Ad+ via a strong CH⋅⋅⋅O ionic H‐bond supported by charge–dipole forces. Although W further enhances the acidity of this CH group along with a proton shift toward the solvent, the proton remains with Ad+ in the monohydrate. We infer essentially free internal W rotation from rotational fine structure of the ν3 band of W, resulting from weak angular anisotropy of the Ad+–W potential., C−H bond activation and free internal rotation: The infrared spectrum of the monohydrated adamantane cation reveals the hydration‐induced activation of its acidic C−H bond. Despite the strong CH⋅⋅⋅O ionic hydrogen bond in this prototypical reaction intermediate, the water ligand undergoes essentially free internal rotation because of weak angular anisotropy of the intermolecular bond.

The photolysis of diazoalkanes is a timely strategy to conduct carbene‐transfer reactions under mild and metal‐free reaction conditions, and has developed as an important alternative to conventional metal‐catalyzed carbene‐transfer reactions. One of the major limitations lies within the rapidly occurring side reaction of the carbene intermediate with remaining diazoalkane molecules that result in the use of an excess of the reaction partner and thus impacts on the reaction efficiency. Herein, we describe a protocol that takes advantage of the in situ generation of donor–acceptor diazoalkanes by Bamford–Stevens reaction. Following this strategy, the concentration of the diazoalkane reaction partner can be minimized to reduce unwanted side reactions and to now conduct photochemical carbene transfer reactions under stoichiometric reaction conditions. We have explored this approach in the C−H and N−H functionalization and cyclopropanation reaction of N‐heterocycles and could demonstrate the applicability of this method in 51 examples., Cyclopropanation: Bamford–Stevens reactions in the presence of blue light open up a pathway to overcome typical limitations of photochemical carbene‐transfer reactions. Following this methodology, the C−H functionalization of indole heterocycles can be performed in high efficiency under stoichiometric conditions (see scheme).

Chemicals for the scouring and bleaching of fabrics have a high environmental load. In addition, in recent years, the high consumption of these products has become a problem in the manufacture of natural fabric products. Therefore, environmentally friendly, low-waste processes for fabric treatment are required. In this paper, we discuss the bleaching of fabrics using advanced oxidation processes (AOP). These processes use electrochemically generated aqueous ozone and ultraviolet (UV) irradiation to achieve bleaching. However, colour reversion often occurs. In this study, we suppressed unwanted colour reversion by treatment with rongalite. After treatment, changes in fabric colour were determined by measuring the colour difference and reflectance spectra. The best bleaching effect was obtained when ozone and UV irradiation treatments were combined, achieving results similar to those of a conventional bleaching method after 60 min of UV irradiation. In addition, the AOP treatment resulted in the simultaneous scouring of the fabric, as shown by the increased hydrophilicity of the fabric after AOP treatment. Thus, this AOP process represents a new fabric bleaching process that has an extremely low environmental impact.

PhotoCORMs are light‐triggered compounds that release CO for medical applications. Here, we apply laser spectroscopy in the gas phase to TryptoCORM, a known photoCORM that has been shown to destroy Escherichia coli upon visible‐light activation. Our experiments allow us to map TryptoCORM's photochemistry across a wide wavelength range by using novel laser‐interfaced mass spectrometry (LIMS). LIMS provides the intrinsic absorption spectrum of the photoCORM along with the production spectra of all of its ionic photoproducts for the first time. Importantly, the photoproduct spectra directly reveal the optimum wavelengths for maximizing CO ejection, and the extent to which CO ejection is compromised at redder wavelengths. A series of comparative studies were performed on TryptoCORM‐CH3CN which exists in dynamic equilibrium with TryptoCORM in solution. Our measurements allow us to conclude that the presence of the labile CH3CN facilitates CO release over a wider wavelength range. This work demonstrates the potential of LIMS as a new methodology for assessing active agent release (e.g. CO, NO, H2S) from light‐activated prodrugs., CO release: The application of a new technique, laser‐interfaced mass spectrometry, for characterizing the ability of a PhotoCORM (CORM=carbon monoxide releasing molecule) to release CO as a function of excitation wavelength is demonstrated. This approach also reveals the identity of the photoproducts, and has potential for application to a wide range of light‐activated prodrugs.

The theoretical self‐healing capacity of new sulfenamide‐based disulfides is estimated by using theoretical methods of quantum chemistry. Starting from previously studied aromatic disulfides, the influence of inserting a NH group between the disulfide and the phenyl ring (forming the sulfenamide), as well as the role of the phenyl ring in the self‐healing process is analyzed. Three parameters are used in the evaluation of the self‐healing capacity: i) the probability to generate sulfenyl radicals, which is the first step of the process; ii) the effect of the hydrogen bonding, which affects the mobility of the chains; and iii) the height of the exchange reaction barrier. The insertion of the NH group notably decreases the bond dissociation energy and, therefore, increases the probability to produce sulfenyl radicals and helps the approach of these radicals to neighboring disulfides, favoring the self‐healing process. The role of the phenyl rings is clearly observed in the reaction barriers, where the π–π stacking interactions notably stabilize the transition states, resulting in larger rate constants. Nevertheless, this stabilization is somewhat reduced in the aromatic sulfenamides, owing to a less effective π–π interaction. Therefore, the sulfenamide‐based aromatic disulfides may be considered as promising candidates for the design of efficient self‐healing materials.

The septet ground state trinitrenes 1,3,5‐trichloro‐2,4,6‐trinitrenobenzene and 1,3,5‐tribromo‐2,4,6‐trinitrenobenzene were isolated in inert (Ar, Ne, and Xe) as well as reactive matrices (H2, O2, and H2O) at cryogenic temperatures. These trinitrenes were obtained in high yields by UV photolysis of the corresponding triazides and characterized by IR and UV/Vis spectroscopy. The trinitrenes, despite bearing six unpaired electrons, are remarkably unreactive towards molecular oxygen and hydrogen and are persistent in water ice up to 160 K where the water matrix starts to sublime off., The magnificent septet: Septet trinitrenes with six unpaired electrons are unreactive toward molecular oxygen and hydrogen and persistent in water ice up to 160 K. The high yields and stability of the septet trinitrenes combined with the large magnetic interaction between the three nitrene units makes these molecules promising building blocks for the design of organic magnetic materials.

A systematic study on quinoline???derived light sensitive probes, having third???order rotational symmetry is presented. The electronically linked octupolar structures show considerably improved linear and nonlinear photophysical properties under one??? and two???photon irradiation conditions compared to the corresponding monomers. Photolysis of the three acetate derivatives shows strong structure dependency: whereas irradiation of the 6??? and 7???aminoquinoline derivatives resulted in fast intramolecular cyclization and only trace amounts of fragmentation products, the 8???aminoquinoline derivative afforded clean and selective photolysis, with a sequential release of their acetate groups (?? u [730]=0.67???GM).

The influence of the spin on the mode of binding between carbon dioxide (CO2) and a transition‐metal (TM) center is an entirely open question. Herein, we use an iron(III) oxalato complex with nearly vanishing doublet–sextet gap, and its ultrafast photolysis, to generate TM‐CO2 bonding patterns and determine their structure in situ by femtosecond mid‐infrared spectroscopy. The formation of the nascent TM‐CO2 species according to [L4FeIII(C2O4)]+ + hν → [L4Fe(CO2)]+ + CO2, with L4=cyclam, is evidenced by the coincident appearance of the characteristic asymmetric stretching absorption of the CO2‐ligand between 1600 cm−1 and 1800 cm−1 and that of the free CO2‐co‐fragment near 2337 cm−1. On the high‐spin surface (S=5/2), the product complex features a bent carbon dioxide radical anion ligand that is O‐“end‐on”‐bound to the metal. In contrast, on the intermediate‐spin and low‐spin surfaces, the product exhibits a “side‐on”‐bound, bent carbon dioxide ligand that has either a partial open‐shell (for S=3/2) or fully closed‐shell character (for S=1/2)., Snapshots from femtosecond mid‐infrared laser spectroscopy reveal spin‐dependent formation of different binding modes of carbon dioxide to a transition‐metal center. The ultrafast excitation of an iron(III) oxalate precursor complex with ultraviolet pulses releases a neutral carbon dioxide molecule within 500 fs and generates a nascent iron‐CO2‐primary complex that isomerizes on a picosecond time scale.

The sensitized photoexcitation of 2-diazocyclopentane-1,3-diones in the presence of THF leads to the insertion of the terminal N-atom of the diazo group into the α-С–Н bond of THF, producing the associated N-alkylhydrazones in yields of up to 63–71%. Further irradiation of hydrazones derived from furan-fused tricyclic diazocyclopentanediones culminates in the cycloelimination of furans to yield 2-N-(alkyl)hydrazone of cyclopentene-1,2,3-trione. By contrast, the direct photolysis of carbocyclic diazodiketones gives only Wolff rearrangement products with up to 90–97% yield.

Marine aerosols consist of a variety of compounds and play an important role in many atmospheric processes. In the present study, sodium iodide clusters with their simple isotope pattern serve as model systems for laboratory studies to investigate the role of iodide in the photochemical processing of sea‐salt aerosols. Salt clusters doped with camphor, formate and pyruvate are studied in a Fourier transform ion cyclotron resonance mass spectrometer (FT‐ICR MS) coupled to a tunable laser system in both UV and IR range. The analysis is supported by ab initio calculations of absorption spectra and energetics of dissociative channels. We provide quantitative analysis of IRMPD measurements by reconstructing one‐photon spectra and comparing them with the calculated ones. While neutral camphor is adsorbed on the cluster surface, the formate and pyruvate ions replace an iodide ion. The photodissociation spectra revealed several wavelength‐specific fragmentation pathways, including the carbon dioxide radical anion formed by photolysis of pyruvate. Camphor and pyruvate doped clusters absorb in the spectral region above 290 nm, which is relevant for tropospheric photochemistry, leading to internal conversion followed by intramolecular vibrational redistribution, which leads to decomposition of the cluster. Potential photodissociation products of pyruvate in the actinic region may be formed with a cross section of

A combined spectroscopic and computational study of gas-phase Au+(CH4) n (n = 3–8) complexes reveals a strongly-bound linear Au+(CH4)2 core structure to which up to four additional ligands bind in a secondary coordination shell. Infrared resonance-enhanced photodissociation spectroscopy in the region of the CH4 a 1 and t 2 fundamental transitions reveals essentially free internal rotation of the core ligands about the H4C–Au+–CH4 axis, with sharp spectral features assigned by comparison with spectral simulations based on density functional theory. In separate experiments, vibrationally-enhanced dehydrogenation is observed when the t 2 vibrational normal mode in methane is excited prior to complexation. Clear infrared-induced enhancement is observed in the mass spectrum for peaks corresponding 4u below the mass of the Au+(CH4) n=2,3 complexes corresponding, presumably, to the loss of two H2 molecules.

Flavin‐based catalysts are photoactive in the visible range which makes them useful in biology and chemistry. Herein, we present electrospray‐ionization mass‐spectrometry detection of short‐lived intermediates in photooxidation of toluene catalysed by flavinium ions (Fl+). Previous studies have shown that photoexcited flavins react with aromates by proton‐coupled electron transfer (PCET) on the microsecond time scale. For Fl+, PCET leads to FlH.+ with the H‐atom bound to the N5 position. We show that the reaction continues by coupling between FlH.+ and hydroperoxy or benzylperoxy radicals at the C4a position of FlH.+. These results demonstrate that the N5‐blocking effect reported for alkylated flavins is also active after PCET in these photocatalytic reactions. Structures of all intermediates were fully characterised by isotopic labelling and by photodissociation spectroscopy. These tools provide a new way to study reaction intermediates in the sub‐second time range., Active site switch occurred after N5‐hydrogen blocking which resulted from proton coupled electron transfer. The short‐lived peroxy‐flavinium reaction intermediates were characterised by mass spectrometry and ion spectroscopy. Although the effect of N5‐hydrogen blocking was predicted more than 40 years ago, this is the first direct evidence.

Efficient solar energy storage is a key challenge in striving toward a sustainable future. For this reason, molecules capable of solar energy storage and release through valence isomerization, for so‐called molecular solar thermal energy storage (MOST), have been investigated. Energy storage by photoconversion of the dihydroazulene/vinylheptafulvene (DHA/VHF) photothermal couple has been evaluated. The robust nature of this system is determined through multiple energy storage and release cycles at elevated temperatures in three different solvents. In a nonpolar solvent such as toluene, the DHA/VHF system can be cycled more than 70 times with less than 0.01 % degradation per cycle. Moreover, the [Cu(CH3CN)4]PF6‐catalyzed conversion of VHF into DHA was demonstrated in a flow reactor. The performance of the DHA/VHF couple was also evaluated in prototype photoconversion devices, both in the laboratory by using a flow chip under simulated sunlight and under outdoor conditions by using a parabolic mirror. Device experiments demonstrated a solar energy storage efficiency of up to 0.13 % in the chip device and up to 0.02 % in the parabolic collector. Avenues for future improvements and optimization of the system are also discussed.

The base-mediated photochemical cyclization of 2-azidobenzoic acids with the formation of 2,1-benzisoxazole-3(1H)-ones is reported. The optimization and scope of this cyclization reaction is discussed. It is shown that an essential step of the ring closure of 2-azidobenzoic acids is the formation and photolysis of 2-azidobenzoate anions.

Coupling of readily available boronic acids and diazo compounds has emerged recently as a powerful metal‐free carbon–carbon bond forming method. However, the difficulty in forming the unstable diazo compound partner in a mild fashion has hitherto limited their general use and the scope of the transformation. Here, we report the application of oxadiazolines as precursors for the generation of an unstable family of diazo compounds using flow UV photolysis and their first use in divergent protodeboronative and oxidative C(sp2)−C(sp3) cross‐coupling processes, with excellent functional‐group tolerance.

Beilstein journal of organic chemistry 13, 1463-1469(2017). doi:10.3762/bjoc.13.144, Published by Beilstein-Institut zur Förderung der Chemischen Wissenschaften, Frankfurt, Main

Recent progress in synthetic chemistry and molecular quantum optics has enabled demonstrations of the quantum mechanical wave–particle duality for complex particles, with masses exceeding 10 kDa. Future experiments with even larger objects will require new optical preparation and manipulation methods that shall profit from the possibility to cleave a well-defined molecular tag from a larger parent molecule. Here we present the design and synthesis of two model compounds as well as evidence for the photoinduced beam depletion in high vacuum in one case.

Photoremovable protecting groups (PPGs) when conjugated to biological effectors forming "caged compounds" are a powerful means to regulate the action of physiologically active messengers in vivo through 1-photon excitation (1PE) and 2-photon excitation (2PE). Understanding the photodeprotection mechanism is important for their physiological use. We compared the quantum efficiencies and product outcomes in different solvent and pH conditions for the photolysis reactions of (8-chloro-7-hydroxyquinolin-2-yl) methyl acetate (CHQ-OAc) and (8-bromo-7-hydroxyquinolin-2-yl)methyl acetate (BHQ-OAc), representatives of the quinoline class of phototriggers for biological use, and conducted nanosecond time-resolved spectroscopic studies using transient emission (ns-EM), transient absorption (ns-TA), transient resonance Raman (ns-TR 2), and time-resolved resonance Raman (ns-TR 3) spectroscopies. The results indicate differences in the photochemical mechanisms and product outcomes, and reveal that the triplet excited state is most likely on the pathway to the product and that dehalogenation competes with release of acetate from BHQ-OAc, but not CHQ-OAc. A high fluorescence quantum yield and a more efficient excited-state proton transfer (ESPT) in CHQ-OAc compared to BHQ-OAc explain the lower quantum efficiency of CHQ-OAc relative to BHQ-OAc. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim., link_to_OA_fulltext

Reactivities of non‐heme iron(IV)‐oxo complexes are mostly controlled by the ligands. Complexes with tetradentate ligands such as [(TPA)FeO]2+ (TPA=tris(2‐pyridylmethyl)amine) belong to the most reactive ones. Here, we show a fine‐tuning of the reactivity of [(TPA)FeO]2+ by an additional ligand X (X=CH3CN, CF3SO3 −, ArI, and ArIO; ArI=2‐(tBuSO2)C6H4I) attached in solution and reveal a thus far unknown role of the ArIO oxidant. The HAT reactivity of [(TPA)FeO(X)]+/2+ decreases in the order of X: ArIO > MeCN > ArI ≈ TfO−. Hence, ArIO is not just a mere oxidant of the iron(II) complex, but it can also increase the reactivity of the iron(IV)‐oxo complex as a labile ligand. The detected HAT reactivities of the [(TPA)FeO(X)]+/2+ complexes correlate with the Fe=O and FeO−H stretching vibrations of the reactants and the respective products as determined by infrared photodissociation spectroscopy. Hence, the most reactive [(TPA)FeO(ArIO)]2+ adduct in the series has the weakest Fe=O bond and forms the strongest FeO−H bond in the HAT reaction., The reaction kinetics of H‐atom transfer mediated by iron(IV)oxo complexes with different cis‐ligands can be studied in a modular flow reactor coupled to MS detection. The HAT reactivity correlates with the intrinsic properties of the isolated complexes in the gas phase. A ligand with a larger binding energy forms a more reactive complex for the HAT reactions, has a weaker FeIV=O bond, and forms a stronger FeIIIO−H bond after the HAT reaction.

25 pags., 15 figs., 4 tabs., Aims. We aim to constrain the sizes of, and investigate deviations from spherical symmetry in, the CO circumstellar envelopes (CSEs) of 16 S-type stars, along with an additional 7 and 4 CSEs of C-type and M-type AGB stars, respectively. Methods. We map the emission from the CO J = 2-1 and 3-2 lines observed with the Atacama Compact Array (ACA) and its total power (TP) antennas, and fit with a Gaussian distribution in the uv- and image planes for ACA-only and TP observations, respectively. The major axis of the fitted Gaussian for the CO(2-1) line data gives a first estimate of the size of the CO-line-emitting CSE. We investigate possible signs of deviation from spherical symmetry by analysing the line profiles and the minor-to-major axis ratio obtained from visibility fitting, and by investigating the deconvolved images. Results. The sizes of the CO-line-emitting CSEs of low-mass-loss-rate (low-MLR) S-type stars fall between the sizes of the CSEs of C-stars, which are larger, and those of M-stars, which are smaller, as expected because of the differences in their respective CO abundances and the dependence of the photodissociation rate on this quantity. The sizes of the low-MLR S-type stars show no dependence on circumstellar density, as measured by the ratio of the MLR to terminal outflow velocity, irrespective of variability type. The density dependence steepens for S-stars with higher MLRs. While the CO(2-1) brightness distribution size of the low-density S-stars is in general smaller than the predicted photodissociation radius (assuming the standard interstellar radiation field), the measured size of a few of the high-density sources is of the same order as the expected photodissociation radius. Furthermore, our results show that the CO CSEs of most of the S-stars in our sample are consistent with a spherically symmetric and smooth outflow. For some of the sources, clear and prominent asymmetric features are observed which are indicative of intrinsic circumstellar anisotropy. Conclusions. As the majority of the S-type CSEs of the stars in our sample are consistent with a spherical geometry, the CO envelope sizes obtained in this paper will be used to constrain detailed radiative transfer modelling to directly determine more accurate MLR estimates for the stars in our sample. For several of our sources that present signs of deviation from spherical symmetry, further high-resolution observations would be necessary to investigate the nature of, and the physical processes behind, these asymmetrical structures. This will provide further insight into the mass-loss process and its related chemistry in S-type AGB stars., This paper makes use of the following ALMA data: ADS/JAO.ALMA#2018.1.01434.S; ADS/JAO.ALMA#2017.1.00595.S and ADS/JAO.ALMA#2012.1.00524.S. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada), MOST and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. MA acknowledges support from the Nordic ALMA Regional Centre (ARC) node based at Onsala Space Observatory. The Nordic ARC node is funded through Swedish Research Council grant No 2017-00648. This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme under grant agreements No. 883867 [EXWINGS] and 730562 [RadioNet].

[EN] Enrofloxacin (ENR) belongs to the fluoroquinolone (FQ) antibiotics family, which are contaminants of emerging concern frequently found in effluents. Although many works studying photo-Fenton process for FQ degradation have been reported, there are no reports analysing in deep the effect of iron complexation, as well as other metals, towards FQs' photolysis, which, evidently, also contributes in the overall degradation of the pollutant. Therefore, in this work, we report a comparative study between the photochemical fate of ENR and its complex with Fe(III) under simulated sunlight irradiation. In addition, the effect of dissolved oxygen, self-sensitization process, and H2O2 addition on the studied photochemical systems are also investigated. Results indicate that, for free and iron-complexed ENR, singlet oxygen (O-1(2)) is generated from the interaction of its triplet state with ground state oxygen. Half-life time (t(1/2)) of ENR under sun simulated conditions is estimated to be around 22 min, while complexation with iron enhances its photostability, leading to a t(1/2) of 2.1 h. Such finding indicates that at least the presence of iron, might notably increase the residence time of these pollutants in the environment. Eventually, only with the addition of H2O2, the FQ-iron complex is efficiently degraded due to photo-Fenton process even at circumneutral pH values due to the high stability of the formed complex. Finally, after LC/FT-ICR MS analysis, 39 photoproducts are detected, of which the 14 most abundant ones are identified. Results indicate that photoproducts formation is pH and iron dependent., This paper is part of a project that has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 765860 (AQUAlity). The paper reflects only the authors' view and the Agency is not responsible for any use that may be made of the information it contains. M.B. and G. M. acknowledge financial support from the CAP 20-25 I-site project.

Atmospheric emissions of atomic and molecular oxygen have been observed since the middle of 19th century. In the last decades, it has been shown that emissions of excited oxygen atom O(1D) and molecular oxygen in electronically&ndash, vibrationally excited states O2(b1&Sigma, +g, v) and O2(a1&Delta, g, v) are related by a unified photochemical mechanism in the mesosphere and lower thermosphere (MLT). The current paper consists of two parts: a review of studies related to the development of the model of ozone and molecular oxygen photodissociation in the daytime MLT and new results. In particular, the paper includes a detailed description of formation mechanism for excited oxygen components in the daytime MLT and presents comparison of widely used photochemical models. The paper also demonstrates new results such as new suggestions about possible products for collisional reactions of electronically&ndash, vibrationally excited oxygen molecules with atomic oxygen and new estimations of O2(b1&Sigma, +g, v = 0&ndash, 10) radiative lifetimes which are necessary for solving inverse problems in the lower thermosphere. Moreover, special attention is given to the &ldquo, Barth&rsquo, s mechanism&rdquo, in order to demonstrate that for different sets of fitting coefficients its contribution to O2(b1&Sigma, g, v) population is neglectable in daytime conditions. In addition to the review and new results, possible applications of the daytime oxygen emissions are presented, e.g., the altitude profiles O(3P), O3 and CO2 can be retrieved by solving inverse photochemical problems when emissions from electronically vibrationally excited states of O2 molecule are used as proxies.

[EN] The degradation of enrofloxacin (ENR) by direct photolysis, Fenton and solar photo-Fenton processes has been studied in different water matrices, such as ultra-pure water (MQ), tap water (TW) and highly saline water (SW). Reactions have been conducted at initial pH 2.8 and 5.0. At pH = 2.8, HPLC analyses showed a fast removal of ENR by (solar photo)-Fenton treatments in all studied water matrices, whereas a 40% removal was observed after 120 min of photolysis. However, TOC measurements showed that only solar photo-Fenton was able to produce significant mineralization (80% after 120 min of treatment); differences between ENR removal and mineralization can be attributed to the release of important amounts of reaction by-products. Excitation-emission matrices (EEMs) combined with parallel factor analysis (PARAFAC) were employed to gain further insight into the nature of these by-products and their time-course profile, obtaining a 5-component model. EEM-PARAFAC results indicated that photolysis is not able to produce important changes in the fluoroquinolone structure, in sharp contrast with (solar photo)-Fenton, where decrease of the components associated with fluoroquinolone core was observed. Agar diffusion tests employing E. toll and S. aureus showed that the antibiotic activity decreased in parallel with the destruction of the fluoroquinolone core., This paper is part of a project that has received funding from the European Union's Horizon 2020 - Research and Innovation Framework Programme under the H2020 Marie Sklodowska-Curie Actions grant agreement No 765860. The paper reflects only the authors' view and the Agency is not responsible for any use that may be made of the information it contains.

The work is devoted to the adaptation of the results of laboratory studies of the laser-induced dissociation of molecules of benzene adsorbed on a quartz substrate to the conditions of the interstellar medium. Adsorption was performed under conditions of low temperature and deep vacuum. The difference between the photolysis of adsorbed molecules and molecules in the gas phase is identified. Significance of process of photolytic desorption in the interstellar conditions is analyzed, in particular, in the conditions of photodissociation regions. It is shown that the efficiency and dissociation channels of photolysis of adsorbed and gas phase benzene differ substantially. It is concluded that the photolysis of aromatic hydrocarbons adsorbed on the interstellar dust grains contributes a negligible fraction to the abundance of small hydrocarbons in the interstellar medium., The original paper is published in Astronomy Reports. The paper includes 17 pages, 3 figures

Direct visualization of electronic and molecular events during chemical and biochemical reactions will offer unprecedented mechanistic insights. Ultrashort pulses produced by X-ray free electron lasers (XFELs) offer an unprecedented opportunity for direct observations of transient events as short-lived as tens of femtoseconds. This paper presents an in-depth analysis of the serial crystallographic datasets collected by Barends & Schlichting et al. (Science 350, 445, 2015) that probe the ligand photodissociation in carbonmonoxy myoglobin (MbCO), a long-serving hallmark for observing ultrafast dynamics in a biological system. This analysis reveals electron density changes that are caused directly by the formation of high-spin 3datomic orbitals of the heme iron upon the CO departure and the dynamic behaviors of these newly formed orbitals in a time series within the first few picoseconds. The heme iron is found vibrating at a high frequency and developing a positional modulation that causes the iron to pop out of and recoil back into the heme plane in succession. These findings here provide long-awaited visual validations for previous works using ultrafast spectroscopy and molecular dynamics simulations. This analysis also extracts electron density variations largely in the solvent during the first period of a low frequency oscillation previously detected by coherence spectroscopy. This work demonstrates the power and importance of the analytical methods in detecting and isolating transient, often very weak signals of electronic changes arising from chemical reactions in proteins.SummaryDirect imaging of ultrafast and subtle structural events during a biochemical reaction, such as a single electronic transition from one atomic or molecular orbital to another, is highly desirable but has been beyond the reach of protein crystallography. It entails the capability of observing changes in electronic distributions at both an ultrafast time scale and an ultrahigh spatial resolution (Itatani et al., Nature 432, 867, 2004). The recent developments in femtosecond serial crystallography at X-ray free electron lasers (XFELs) have brought the achievable temporal resolution within a striking distance. This paper presents the electron density map decomposed from the XFEL data that shows the remanence of several 3datomic orbitals of the heme iron at an available spatial resolution although the map component is not an accurate image of the atomic orbitals. A key strategy that has enabled the findings here is a numerical deconvolution to resolve concurrent variations in a series of time-resolved electron density maps so that the electron densities influenced by an electron transfer event can be isolated as a partial change from the overwhelming presence of the bulk electrons that are not directly involved in bonding. Even at the limited spatial resolution, the subtle changes in electron distribution due to a spin crossover can be decoupled from far greater changes due to atomic displacements. Direct observations of electronic orbitals could offer unprecedented mechanistic insights into a myriad of chemical and biochemical reactions such as electron transfer in redox reactions, and formation, rupture, and isomerization of chemical bonds.Ligand photodissociation in carbonmonoxy myoglobin (MbCO) has been a benchmark for studying ultrafast protein dynamics in a biological system. A number of studies in time-resolved crystallography have progressively improved the time resolution (from Šrajer et al., Science 274, 1726, 1996 to Barends et al., Science 350, 445, 2015). This paper presents an in-depth analysis of the serial crystallographic datasets of MbCO that Barends & Schlichting et al. (2015) contributed to the Protein Data Bank. First, a component of electron density distributions clearly shows the characteristic shape of the high-spin 3dorbitals reappeared at the heme iron upon the photodissociation of the CO ligand despite the limited accuracy of the orbital image due to the available spatial resolution. Second, the dynamic behaviors of these newly regained 3dorbitals within picoseconds after the photolysis provide long-awaited structural validation for previous spectroscopic observations and computational simulations. Specifically, the newly formed densities are oscillating with the heme iron at a high frequency of a thousand wavenumbers and developing a positional modulation during the first few picoseconds (Champion, Science 310, 980, 2005). The iron pops out of the heme plane at a few picoseconds and recoils back and pops out again afterwards. The dominant oscillation at a low frequency of several tens wavenumbers previously detected by coherence spectroscopy can be clearly resolved from the time series of electron density maps. The associated changes in electron density during the first cycle of the oscillation are largely located in the solvent rather than on the protein or heme, which suggests that the low frequency oscillations in a number of heme proteins, including MbCO, likely originate from a photolysis triggered pressure wave propagating in the solvated protein. Finally, these findings of chemical signals are isolated from coexisting thermal artifacts also by the numerical deconvolution. It is modeled in this study that the ultrashort XFEL pulses cause a transient spike of the local temperature at the heme site of hundreds of K.

In their comment to our recent paper about low HONO and NO2 formation by photolysis of adsorbed HNO3 Sullivan et al. confirmed their former results of HNO3 adsorption on silica under dry conditions using a quartz crystal microbalance. The authors concluded that the differences between their results and our conclusions are caused by the different experimental conditions, i.e. adsorption under very dry conditions compared to our experiments at 50% r.h. While we agree that adsorption of the highly water soluble HNO3 will strongly depend on humidity, there is still the conflict in the photolysis frequency of adsorbed HNO3 under atmospheric conditions to which the authors referred in their previous publications (see their atmospheric implication sections) and to which also our paper refers. If their results on both the adsorption cross sections of HNO3 (two to three orders of magnitude larger compared to the gas phase) and the quantum yield for NO2 formation (close to unity) are applicable under conditions prevailing in the atmosphere, then the photolytic lifetime of HNO3 on surfaces would be only ∼5 min for atmospheric solar flux (0° SZA), which is highly unlikely.

As air pollution poses a great challenge around the globe, it is essential to fashion out a way of efficiently degrading the air pollutants. Vacuum Ultraviolet (VUV)-based processes are an emerging and promising technology for environmental remediation such as air cleaning, wastewater treatment, and air/water disinfection. When VUV irradiation, photolysis, photocatalysis, and ozone-assisted oxidation are involved at the same time, it results in the fast degradation of air pollutants because of their strong oxidizing capacity. The mechanisms of how the oxidants are produced and how they react are discussed in this review. This paper focuses mainly on the three VUV-based oxidation processes including VUV photolysis, VUV combined with ozone-assisted oxidation, and VUV-PCO with emphasis on their mechanisms and applications. Also, the outlook of these processes are proposed in this paper.

This paper opens a series in which the photochemistry of the two lowest πσ* states of pyrrole and their interaction with each other and with the ground electronic state X are studied using ab initio quantum mechanics. New 24-dimensional potential energy surfaces for the photodissociation of the N–H bond and the formation of the pyrrolyl radical are calculated using the multiconfigurational perturbation theory (CASPT2) for the electronic states X(ππ), 11A2(πσ*), and 11B1(πσ*) and locally diabatized. In this paper, the ab initio calculations are described and the photodissociation in the state 11A2(πσ*) is analyzed. The excitation 11 A2←X is mediated by the coordinate dependent transition dipole moment functions constructed using the Herzberg-Teller expansion. Nuclear dynamics, including 6, 11, and 15 active degrees of freedom, are studied using the multi-configurational time-dependent Hartree method. The focus is on the frequency resolved absorption spectrum as well as on the dissociation time scales and the resonance lifetimes. Calculations are compared with available experimental data. An approximate convolution method is developed and validated, with which absorption spectra can be calculated and assigned in terms of vibrational quantum numbers. The method represents the total absorption spectrum as a convolution of the diffuse spectrum of the detaching H-atom and the Franck-Condon spectrum of the heteroaromatic ring. Convolution calculation requires a minimal quantum chemical input and is a promising tool for studying the πσ* photodissociation in model biochromophores.This paper opens a series in which the photochemistry of the two lowest πσ* states of pyrrole and their interaction with each other and with the ground electronic state X are studied using ab initio quantum mechanics. New 24-dimensional potential energy surfaces for the photodissociation of the N–H bond and the formation of the pyrrolyl radical are calculated using the multiconfigurational perturbation theory (CASPT2) for the electronic states X(ππ), 11A2(πσ*), and 11B1(πσ*) and locally diabatized. In this paper, the ab initio calculations are described and the photodissociation in the state 11A2(πσ*) is analyzed. The excitation 11 A2←X is mediated by the coordinate dependent transition dipole moment functions constructed using the Herzberg-Teller expansion. Nuclear dynamics, including 6, 11, and 15 active degrees of freedom, are studied using the multi-configurational time-dependent Hartree method. The focus is on the frequency resolved absorption spectrum as well as on the dissociation time scales an...

Carbon monoxide is the most abundant molecule after H$_2$ and is important for chemistry in circumstellar envelopes around late-type stars. The size of the envelope is important when modelling low-J transition lines and deriving mass-loss rates from such lines. Now that ALMA is coming to full power the extent of the CO emitting region can be measured directly for nearby asymptotic giant branch (AGB) stars. In parallel, it has become obvious in the past few years that the strength of the interstellar radiation field (ISRF) can have a significant impact on the interpretation of the emission lines. In this paper an update and extension of the classical Mamon et al. (1988; ApJ 328, 797) paper is presented; these authors provided the CO abundance profile, described by two parameters, as a function of mass-loss rate and expansion velocity. Following recent work an improved numerical method and updated H$_2$ and CO shielding functions are used and a larger grid is calculated that covers more parameter space, including the strength of the ISRF. The effect of changing the photodissociation radius on the low-J CO line intensities is illustrated in two cases., Comment: A&A in press

International audience; The relative importance of crosslinking and chain scissions reactions involved in the photothermal ageing of polycarbonates is shown to depend on the chemical structure of the polymer. The orientation of these reactions is linked to the modifications of the chemical structure resulting from photolysis, photooxidation and thermooxidation. In this paper, the effects of crosslinking and chain scission of tetramethyl bisphenol-A polycarbonate (TMPC) are determined by size exclusion chromatography (SEC) and gel fraction measurements. These evolutions are correlated to the modifications of the chemical structure observed by FTIR spectroscopy.The presence of the four ortho-methyl substituants on the aromatic rings accounts for the difference in the photothermal ageing of TMPC compared to bisphenol-A polycarbonate (PC). Tetramethyl substitution inhibits photo-Fries rearrangements in TMPC, but in contrast these methyl groups involve crosslinks under irradiation and are the source of a higher oxidizability of TMPC compared to PC. A proposal for the various routes accounting for the crosslinking and the formation of the oxidation products in TMPC is reported in this paper.

We present Herschel spectroscopy of atomic lines arising in photodissociation regions as well as ionization regions of nearby early-type galaxies (ETGs), focusing on the volume-limited Atlas3D sample. Our data include the [CII], [OI], and [NII] 122 and 205 micron lines, along with ancillary data including CO and HI maps. We find ETGs have [CII]/FIR ratios slightly lower than spiral galaxies in the KINGFISH sample, and several ETGs have unusually large [NII] 122/[CII] ratios. The [NII] 122/[CII] ratio is correlated with UV colors and there is a strong anti-correlation of [CII]/FIR with NUV-K seen in both spirals and ETGs, likely due to a softer radiation field with fewer photons available to ionize carbon and heat the gas. The correlation thus makes a [CII] deficit in galaxies with redder stellar populations. The high [NII] 122/[CII] (and low [CII]/FIR) line ratios could also be affected by the removal of much of the diffuse, low density gas, which is consistent with the low HI/H2 ratios. [CII] is now being used as a star formation indicator, and we find it is just as good for ETGs as in spirals. The [CII]/CO ratios found are also similar to those found in spiral galaxies. Through use of the [NII] 205 micron line, estimates of the percentage of [CII] emission arising from ionized gas indicate a significant portion could arise in ionized regions., Comment: This paper has been accepted to ApJ. The paper should be 24 pages and contains 16 figures

The speed and angular distribution of O atoms arising from the photofragmentation of C(5)H(8)-O(2), the isoprene-oxygen van der Waals complex, in the wavelength region of 213-277 nm has been studied with the use of a two-color dissociation-probe method and the velocity map imaging technique. Dramatic enhancement in the O atoms photo-generation cross section in comparison with the photodissociation of individual O(2) molecules has been observed. Velocity map images of these "enhanced" O atoms consisted of five channels, different in their kinetic energy, angular distribution, and wavelength dependence. Three channels are deduced to be due to the one-quantum excitation of the C(5)H(8)-O(2) complex into the perturbed Herzberg III state ((3)Δ(u)) of O(2). This excitation results in the prompt dissociation of the complex giving rise to products C(5)H(8)+O+O when the energy of exciting quantum is higher than the complex photodissociation threshold, which is found to be 41740 ± 200 cm(-1) (239.6±1.2 nm). This last threshold corresponds to the photodissociation giving rise to an unexcited isoprene molecule. The second channel, with threshold shifted to the blue by 1480 ± 280 cm(-1), corresponds to dissociation with formation of rovibrationally excited isoprene. A third channel was observed at wavelengths up to 243 nm with excitation below the upper photodissociation threshold. This channel is attributed to dissociation with the formation of a bound O atom C(5)H(8)-O(2) + hv → C(5)H(8)-O(2)((3)Δ(u)) → C(5)H(8)O + O and/or to dissociation of O(2) with borrowing of the lacking energy from incompletely cooled complex internal degrees of freedom C(5)H(8)*-O(2) + hv → C(5)H(8)*-O(2)((3)Δ(u)) → C(5)H(8) + O + O. The kinetic energy of the O atoms arising in two other observed channels corresponds to O atoms produced by photodissociation of molecular oxygen in the excited a (1)Δ(g) and b (1)Σ(g)(+) singlet states as the precursors. This indicates the formation of singlet oxygen O(2)(a (1)Δ(g)) and O(2)(b (1)Σ(g)(+)) after excitation of the C(5)H(8)-O(2) complex. Cooperative excitation of the complex with a simultaneous change of the spin of both partners (1)X-(3)O(2) + hν → (3)X-(1)O(2) → (3)X + (1)O(2) is suggested as a source of singlet oxygen O(2)(a (1)Δ(g)) and O(2)(b (1)Σ(g)(+)). This cooperative excitation is in agreement with little or no vibrational excitation of O(2)(a (1)Δ(g)), produced from the C(5)H(8)-O(2) complex as studied in the current paper as well as from the C(3)H(6)-O(2) and CH(3)I-O(2) complexes reported in our previous paper [Baklanov et al., J. Chem. Phys. 126, 124316 (2007)]. The formation of O(2)(a (1)Δ(g)) from C(5)H(8)-O(2) was observed at λ(pump) = 213-277 nm with the yield going down towards the long wavelength edge of this interval. This spectral profile is interpreted as the red-side wing of the band of a cooperative transition (1)X-(3)O(2) + hν → (3)X(T(2))-(1)O(2)(a (1)Δ(g)) in the C(5)H(8)-O(2) complex.

International audience; The stability of the ground or excited state calcium atom in an argon-doped helium droplet has been investigated using an extension of the helium density functional method to treat clusters. This work was motivated by the experimental study presented in a companion paper, hereafter called Paper I [A. Masson, M. Briant, J. M. Mestdagh, M. A. Gaveau, A. Hernando, and N. Halberstadt, J. Chem. Phys. 137, 184310 (2012)10.1063/1.4762836], which investigated Ca2 photodissociation in an argon-doped helium droplet and the nature of the fluorescent species. It is found that one single argon atom is sufficient to bring the calcium atom inside the droplet, for droplets of over 200 helium atoms. The absorption and emission spectra of CaArM (M = 0-7) clusters have been simulated using the recently developed density sampling method to describe the influence of the helium environment. Absorption spectra exhibit broad, double bands that are significantly blueshifted with respect to the calcium atomic line. The emission spectra are less broad and redshifted with respect to the calcium resonance line. The shifts are found to be additive only for M ⩽ 2, because only the first two argon atoms are located in equivalent positions around the calcium p orbital. This finding gives a justification for the fit presented in the companion paper, which uses the observed shifts in the emission spectra as a function of argon pressure to deduce the shifts as a function of the number of argon atoms present in the cluster. An analysis of this fit is presented here, based on the calculated shifts. It is concluded that the emitting species following Ca2 photodissociation in an argon-doped droplet in Paper I could be Ca*ArM in a partly evaporated droplet where less than 200 helium atoms remain.

Nitrocellulose membrane (NCM) can produce hydroxyl radicals under illumination, which promotes the oxidative degradation of organic pollutants. In this paper, NCM was used to oxidize bisphenol A (BPA) under simulated sunlight. The effects of pH, temperature, light intensity, anion and cation on the degradation of BPA were analyzed. The photodegradation process of BPA was discussed. The optimal photolysis rate was 0.031 min−1 when the temperature was 30°C, the light intensity was 2.67 × 104 Lux, and the pH value was 9.0. The alkaline environment, temperature and light intensity can promote the photodegradation of BPA. Except for nitrate ions, anions and cations can inhibit the photodegradation of BPA. Compared with cations, anions have a greater inhibitory effect on BPA degradation. The degradation products of BPA by NCM were analyzed by gas chromatographic/mass. This study may provide useful information for the BPA degradation by NCM in complex water samples.

Improving knowledge of the ozone global distributions in the mesosphere–lower thermosphere (MLT) is a crucial step in understanding the behaviour of the middle atmosphere. However, the concentration of ozone under sunlit conditions in the MLT is often so low that its measurement requires instruments with very high sensitivity. Fortunately, the bright oxygen airglow can serve as a proxy to retrieve the daytime ozone density indirectly, due to the strong connection to ozone photolysis in the Hartley band. The OSIRIS IR imager (hereafter, IRI), one of the instruments on the Odin satellite, routinely measures the oxygen infrared atmospheric band (IRA band) at 1.27 µm. In this paper, we will primarily focus on the detailed description of the steps done for retrieving the calibrated IRA band limb radiance (with

Astronomical observations indicate a high abundance of methanol molecules in the gas phase of molecular-cloud dense cores, which cannot be explained by gas-phase chemical reactions only. A significant contribution to the methanol abundance should be provided by chemical reactions on the dust particle surface with subsequent desorption of the produced molecules into the gas phase. For the development and refinement of models involving these processes, laboratory studies of photo-induced processes occurring in the adsorbed material are necessary. In this paper, the experiment results of adsorbed methanol molecules are presented. A methanol molecule monolayer, physically adsorbed on fused silica surface cooled by liquid nitrogen (Т ∼ 100 K), was irradiated in high vacuum by nanosecond pulses of an excimer KrF laser with a fixed wavelength λ = 248 nm. The photodissociation products of three-photon laser excitation were recorded by a quadrupole mass spectrometer. Relative yields of photofragments H, OH, and CH3 were determined. Photolysis of partially deuterated CH3OH molecules has shown that hydrogen atoms can be ejected both from hydroxyl and methyl groups. In contrast to the isolated molecule photolysis in the gas phase and dissociation of the multilayer molecular coatings, photoexcitation of adsorbed methanol monolayer even in the energy region of 10 eV does not cause noticeable chemical transformations and does not lead to the formation of molecular components H2 and CH4. Due to existing astrochemical modeling problems, possible application methods of the obtained laboratory results are considered.

Incorporation of fluorescent proteins into biochemical systems has revolutionized the field of bioimaging. In a bottom-up approach, understanding the photophysics of fluorescent proteins requires detailed investigations of the light-absorbing chromophore, which can be achieved by studying the chromophore in isolation. This paper reports a photodissociation action spectroscopy study on the deprotonated anion of the red Kaede fluorescent protein chromophore, demonstrating that at least three isomers-assigned to deprotomers-are generated in the gas phase. Deprotomer-selected action spectra are recorded over the S1 ← S0 band using an instrument with differential mobility spectrometry coupled with photodissociation spectroscopy. The spectrum for the principal phenoxide deprotomer spans the 480-660 nm range with a maximum response at ≈610 nm. The imidazolate deprotomer has a blue-shifted action spectrum with a maximum response at ≈545 nm. The action spectra are consistent with excited state coupled-cluster calculations of excitation wavelengths for the deprotomers. A third gas-phase species with a distinct action spectrum is tentatively assigned to an imidazole tautomer of the principal phenoxide deprotomer. This study highlights the need for isomer-selective methods when studying the photophysics of biochromophores possessing several deprotonation sites.

Aromatic nitroderivatives are compounds of considerable environmental concern, because some of them are phytotoxic (especially the nitrophenols, and particularly 2,4-dinitrophenol), others are mutagenic and potentially carcinogenic (e.g., the nitroderivatives of polycyclic aromatic hydrocarbons, such as 1-nitropyrene), and all of them absorb sunlight as components of the brown carbon. The latter has the potential to affect the climatic feedback of atmospheric aerosols. Most nitroderivatives are secondarily formed in the environment and, among their possible formation processes, photonitration upon irradiation of nitrate or nitrite is an important pathway that has periodically gained considerable attention. However, photonitration triggered by nitrate and nitrite is a very complex process, because the two ionic species under irradiation produce a wide range of nitrating agents (such as •NO2, HNO2, HOONO, and H2OONO+), which are affected by pH and the presence of organic compounds and, in turn, deeply affect the nitration of aromatic precursors. Moreover, aromatic substrates can highly differ in their reactivity towards the various photogenerated species, thereby providing different behaviours towards photonitration. Despite the high complexity, it is possible to rationalise the different photonitration pathways in a coherent framework. In this context, this review paper has the goal of providing the reader with a guide on what to expect from the photonitration process under different conditions, how to study it, and how to determine which pathway(s) are prevailing in the formation of the observed nitroderivatives.

In this paper, the synergistic effects of advanced oxidization reactions in a combination of TiO2 photocatalysis are comparatively investigated for hydrogen production and wastewater treatment applications. An experimental study is conducted with a photoelectrochemical reactor under a UV-light source. TiO2 is selected as the photocatalyst due to the high corrosion resistant nature and ability to form hydroxyl radicals with the interaction with photons. The synergetic effects of advanced oxidization processes (AOPs) such as Fenton, Fenton-like, photocatalysis (TiO2/UV) and UV photolysis (H2O2/UV) are investigated individually and in a combination of each other. The Fenton type reagent in the reactor is formed by anodic sacrificial of stainless-steel electrode with the presence of H2O2. The influences of various parameters, including pH level, type of the electrode and electrolyte and the UV light, on the performance of the combined system are also investigated experimentally. The highest chemical oxygen demand (COD) removal efficiency is observed as 97.9% for the experimental condition which combines UV/TiO2, UV/H2O2 and photo-electro Fenton type processes. The maximum hydrogen production rate from the photoelectrolysis of wastewater is obtained as 7.0 mg/Wh for the experimental condition which has the highest rate of photo-electro Fenton type processes. The average enhancement with the presence of UV light on hydrogen production rates and COD removal efficiencies are further calculated to be 3% and 20%, respectively.

The study of atmospheric nitrous acid (HONO), which is the primary source of OH radicals, is crucial with respect to understanding atmospheric photochemistry and heterogeneous chemical processes. Heterogeneous NO2 chemistry under haze conditions has been identified as one of the missing sources of HONO on the North China Plain, and also produces sulfate and nitrate. However, controversy exists regarding the various proposed HONO production mechanisms, mainly regarding whether SO2 directly takes part in the HONO production process and what roles NH3 and the pH value play. In this paper, never before seen explosive HONO production was reported and evidence was found – for the first time in field measurements during fog (usually with 4

© 2018 Elsevier. This manuscript version is made available under the CC-BY-NC-ND 4.0 license: http://creativecommons.org/licenses/by-nc-nd/4.0/ 24 month embargo from date of publication (March 2019) per publisher’s policy, The atmosphere of Jupiter is mainly hydrogen and methane, with a large number of hydrocarbons calculated to be produced by photodissociation and subsequent reactions. It is assumed that oxygen is added by meteoroids. Recent studies have found that photochemistry does not explain the measured ratios of water to carbon monoxide, if it is assumed that water is the major constituent of meteoroids and vapourises. A possible explanation is that processes that occur during or soon after the meteoroid's passage change the proportions of the oxygen-bearing constituents. In this paper, the processes considered are dissociation, ionization of the original molecules and ionization of dissociated products. The difference between applying these processes in the bulk atmosphere and in the meteor trail itself is investigated, as is the possibility of methane being dissociated in a shock wave produced by the meteoroid. In all cases, there was no significant change to the predicted density of water at the height of a measurement. However, the density of hydroxyl relative to water differed depending on the assumed process, thus presenting the possibility that measurements of electron-driven emissions from hydroxyl could be used for remote sensing of the actual processes occurring.

Photodissociation of vibrationally and electronically excited sulfur dimer molecules (S2) has been studied in a combined experimental and computational quantum chemistry study in order to characterize bound-continuum transitions. Ab initio quantum chemistry calculations are carried out to predict the potential energy curves, spin-orbit coupling, transition moments, and bound-continuum spectra of S2 for comparison with the experimental data. The experiment uses velocity map imaging to measure S-atom production following S2 photoexcitation in the ultraviolet region (320-205 nm). A pulsed electric discharge in H2S produces ground-state S2 X3ςg -(v = 0-15) as well as electronically excited singlet sulfur and b1ςg +(v = 0, 1), and evidence is presented for the production and photodissociation of S2 a1Δg. In a previous paper, we reported threshold photodissociation of S2X3ςg -(v = 0) in the 282-266 nm region. In the present study, S(3PJ) fine structure branching and angular distributions for photodissociation of S2 (X3ςg -(v = 0), a1Δg and b1ςg +) via the B″3IIu, B3ςu - and 11IIu excited states are reported. In addition, photodissociation of the X3ςg -(v = 0) state of S2 to the second dissociation limit producing S(3P2) + S(1D) is characterized. The present results on S2 photodynamics are compared to those of the well-studied electronically isovalent O2 molecule.

OH-containing and H2-impregnated fused silica is the optical materials of choice for deep-ultraviolet (DUV) applications. Intrinsic and UV laser irradiation induced non-bridging oxygen hole center (NBOHC) defects play a central role in the optical properties of fused silica in the DUV spectra range. Understanding the NBOHC generation mechanism is of great importance to the performance improvement. In this paper, NBOHC-related 650 nm photoluminescence (PL) band is investigated in details by heat-treating the fused silica at different temperature and exciting the PL band at different wavelength. From the 650 nm PL characteristics of un-treated and heat-treated fused silica samples excited at 193 nm, 266 nm, 355 nm, and 532 nm, it is found that the 650 nm PL band of un-treated fused silica is excited at 193 nm and 266 nm mainly via a two-photon process, and cannot be excited with 355 nm and 532 nm. The un-treated fused silica also presented a reversible time delay (annealing) in 650 nm PL intensity following an abrupt change of excitation fluence at 193 nm, due to the recombination of NBOHCs with impregnated H2. On the other hand, for the heat-treated fused silica, the 650 nm PL band is excited by a combination of one- and two-photon processes at 193 nm and 266 nm with the one-photon process dominating, and by the one-photon excitation process at 355 nm and 532 nm. The quantum yield of 650 nm PL band decreases with the decreasing excitation photon energy. From these experimental results it is confirmed with no doubt that in un-treated fused silica NBOHCs are produced by 193 nm and 266 nm laser irradiation induced photolysis of an Si‒OH group via a two-photon process, with a minimum photolysis energy between 7.0 eV and 7.9 eV. In heat-treated fused silica NBOHCs are produced by heat treatment induced breakage of Si‒OH bonds. Heat treatment also removed totally the impregnated H2 in fused silica, that makes the heat-treatment produced NBOHCs become stable and show one-photon excited 650 nm PL band when excited at 193 nm, 266 nm, 355 nm, and 532 nm. In contrary to the un-treated fused silica, the heat-treated fused silica presented no reversible time delay in 650 nm PL intensity following the abrupt change of excitation fluence at 193 nm, due to the total removal of H2 in fused silica and the absence of recombination of NBOHCs with H2.