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• H 2 C NH 2 +Ar ions are produced via pulsed discharge in a supersonic expansion. • The photodissociation spectrum of H 2 C NH 2 +Ar is studied at from 2100 to 4000 cm−1. • Spectra are predicted with Second Order Vibrational Perturbation Theory (VPT2). • Two isomers corresponding to different argon attachment sites are characterized. The methaniminium ion (H 2 C NH 2 +) was produced in a pulsed electrical discharge supersonic expansion of argon saturated with ethylenediamine vapor. It was identified and mass selected in a time-of-flight spectrometer. Its infrared spectrum was measured in the region of 2100–4100 cm−1 by photodissociation of the argon-tagged complex with a tunable infrared OPO/OPA laser system. The observed infrared spectrum was not described well by scaled harmonic theory, but could be assigned by comparison to second order vibrational perturbation theory computations at the B2PLYP/def2-QZVPP level. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • UVPD spectrum of GMPH+ ion was measured by IR-laser ablation of droplet beam. • The three types of anti glycosyl-bond conformations with a keto form were observed. • A quadrupole ion trap with 70 ms trap time is essential for conformer separation. Abstract Photodissociation (PD) spectroscopy of protonated guanosine monophosphate (GMPH+) ions was performed using IR-laser ablation of droplet beam and quadruple ion trap techniques. Photofragmentation of GMPH+ gave a protonated guanine ion (GH+) as the main product. A wide-range PD spectrum (3.9–5.4 eV) monitored by the GH+ ion intensity showed four characteristic electronic transitions related to their three different anti glycosyl-bond conformers of GMPH+, which were identified by their π-π* transitions based on time dependent density functional theory calculation. Furthermore, the narrow-bandwidth PD spectrum (4.28–4.33 eV) shows the existence of syn glycosyl-bond conformation with keto form. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The product state distributions in trimethylamine photodissociation were measured. • The CH 3 photofragments showed dual ring-like scattering distributions. • The slow CH 3 fragment was ascribed to the production of the excited state N(CH 3) 2. • The energy threshold of C N fission was located between the S 2 and S 1 state origins. Abstract The photodissociation dynamics of trimethylamine, N(CH 3) 3 , was studied using ion-imaging. The photolysis wavelength was scanned over the 200–236 nm region, where the S 1 (3 s) and S 2 (3 p) states were excited with varying relative populations. The dissociation threshold of C N bond fission was found at 42,500 cm−1, which is located between the S 1 (3 s) and S 2 (3 p) origins. The final-state distributions were qualitatively insensitive to the photoinitiated states, indicating a dissociation mechanism following ultrafast electronic dynamics. The CH 3 photofragments showed dual ring-like scattering distributions, which were ascribed to branching to the CH 3 + N(CH 3) 2 ( A ∼ 2 A 1) and CH 3 + N(CH 3) 2 ( X ∼ 2 B 1) pathways. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The CH 3 O + H formation occurs easier than CH 2 OH + H on the excited state. • On the lowest excited state, the O H bond elongates easier than the C H bond. • During the C H bond dissociation, CHOH + H 2 can be also generated. • On the ground state, however, the CH 2 OH + H channel occurs easier than CH 3 O + H. • In ices, the fraction of CH 3 OH which dissociates on the ground state would increase. Abstract The photodissociation of methanol, which is an important radical source on interstellar ices, was studied using quantum chemistry calculations. Surface hopping simulations using the time-dependent density functional theory were performed, and the potential energy curves of the low-lying excited states were analyzed using the second-order multireference perturbation theory to reveal the reaction mechanism in the gas phase. We showed that the generation of CH 3 O would more frequently occur than that of CH 2 OH on the S 1 state in contrast to the ground state. We also discuss why the ratio of CH 3 O and CH 2 OH differs between the gas and solid phases. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Aimed at filling the gap in the theoretical studies of the CH 3 's photo-dissociation. • Our results look promising reproducing the same trend as state of the art experiments. • The method used allows the interpretation of the internal mechanisms of the process. Abstract The photodissociation dynamics of methyl radical from selected vibrational levels of the 3 s and 3 p z Rydberg states has been studied using the trajectory surface hopping method on one-dimensional potential energy curves along the carbon-hydrogen dissociative coordinate and the non-adiabatic couplings between them, calculated by ab initio methods. Lifetimes and product distributions have been obtained for all the studied vibrational levels and compared with previous theoretical and experimental works. The theoretical lifetimes tend to decrease as vibrational excitation increases in accordance with experimental results. The agreement, however, is only qualitative considering the reduced dimensionality of the model. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Detection of OH and HO 2 has been demonstrated using FM laser absorption spectroscopy. • Room temperature photolysis of H 2 O 2 at 193 nm in argon has been used as a test system. • The FM sensitivity is estimated to be on the order of 1011 molecule cm−3. • The product branching measured here is in excellent agreement with previous work. Abstract The photodissociation of H 2 O 2 dilute in argon at 193 nm has been investigated using near infrared frequency modulation laser absorption spectroscopy on selected rotational lines of the OH vibrational overtone bands between 6500 and 7100 cm−1 to detect the OH and HO 2 radical products with the same laser. Sequential OH and HO 2 time-dependent profiles have been measured at room temperature and total pressures ranging from 3 to 56 Torr. Kinetic analysis gives the product distribution following H 2 O 2 photolysis of (82 ± 1) % OH and (18 ± 1) % HO 2 under the present conditions, in excellent agreement with previously reported measurements. [ABSTRACT FROM AUTHOR]

Ultraviolet photodissociation dynamics of tricarbonylnitrosylcobalt, Co(CO) 3 NO, is studied by ion-imaging. The photon energy is large enough to eliminate both NO and CO ligands in this heteroleptic complex, among which state-specific scattering is observed in the NO loss channel. The velocity distributions of the NO ligands exhibit clear evidence of two pathways. NO fragments with higher and lower kinetic energies are ascribed to direct dissociation in the electronic excited state and secondary decomposition following relaxation processes, respectively. The state-specific angular distribution of the faster component corroborates the rotational alignment, indicating the bent coordination of the nitrosyl ligand in the photoexcited state. [ABSTRACT FROM AUTHOR]

Infrared spectra of Ca(NH 3 ) n complexes in the gas phase have been recorded for the first time. The spectra are consistent with structures where the Ca atom resides inside one or more solvation shells of NH 3 molecules. IR spectra were recorded using a photodissociation technique. A comparison of the spectra with those predicted from ab initio calculations suggests that Ca(NH 3 ) 8 has all NH 3 molecules in a single solvent shell around the Ca atom, whereas the spectra of Ca(NH 3 ) 9 and Ca(NH 3 ) 10 are consistent with two-shell structures. [ABSTRACT FROM AUTHOR]

In this work the efficacy of semi-classical surface hopping approaches is investigated through studies of the photodissociation dynamics of BrCN − and ICN − . BrCN − provides a challenging situation for semi-classical approaches as excitation to the first bright state yields both Br −  + CN and Br ∗  + CN − products. Further, this branching is highly sensitive to the amount of rotational energy in the CN 0/− fragment. The results of semi-classical and quantum mechanical descriptions of the dynamics are compared when the classical dynamics are propagated in an adiabatic and diabatic representation. The implications of the differences between the classical and quantum treatments of J = 0 are also explored. [ABSTRACT FROM AUTHOR]

We present a combined experimental and theoretical study of the photodissociation of the bisanthenequinone (C 28 H 12 O 2 ) cation, Bq + . The experiments show that, upon photolysis, the Bq + cation does not dehydrogenate, but instead fragments through the sequential loss of the two neutral carbonyl groups, causing the formation of five-membered carbon cycles. Quantum chemical calculations confirm this Bq +   →  [Bq - CO] +   →  [Bq - 2CO] + sequence as the energetically most favorable reaction pathway. For the first CO loss, a transition state with a barrier of ∼3.2 eV is found, substantially lower than the lowest calculated H loss dissociation pathway (∼4.9 eV). A similar situation applies for the second CO loss channel (∼3.8 eV vs. ∼4.7 eV), but where the first dissociation step does not strongly alter the planar PAH geometry, the second step transforms the molecule into a bowl-shaped one. [ABSTRACT FROM AUTHOR]

The one-laser two-color resonance enhanced multiphoton ionization REMPI [(1 + 1′) + 1] and velocity map imaging have been applied to investigate formation of molecular oxygen in excited singlet O 2 ( a 1 Δ g ) and ground O 2 ( X 3 Σ g - ) states in the photodissociation of van der Waals complex isoprene-oxygen C 5 H 8 -O 2 . These molecules were found to appear in the different rotational states with translational energy varied from a value as low as ∼1 meV to a distribution with temperature of about 940 K. The observed traces of electron recoil in the images of photoions reveal participation of several ionization pathways of the resonantly excited intermediate states of O 2 . [ABSTRACT FROM AUTHOR]

The H 2 35 Cl + Ar cation complex was prepared by electrical discharge in a supersonic expansion of argon doped with HCl and hydrogen. The ion was mass selected in a reflectron time-of-flight spectrometer and investigated with infrared photodissociation spectroscopy in the regions of 1000–4550 and 4850–7350 cm −1 . Anharmonic vibrational frequencies were computed with VPT2 at the CCSD(T)/cc-pVTZ level of theory. The previously unreported ν 3 fundamental at 2211 cm −1 and several new combinations and overtones are reported. VPT2 theory at this level confirms the H-bound structure of the complex and provides an accurate description of the anharmonic vibrations in this system. [ABSTRACT FROM AUTHOR]

We reveal the microscopic mechanics of iodide ion microhydration by recording the isotopomer-selective vibrational spectra of the I − ·(H 2 O)·(D 2 O), I − ·(HOD)·(D 2 O), and I − ·(DOH)·(H 2 O) isotopologues using a new class of ion spectrometer that is optimized to carry out two-color, IR-IR photodissociation in a variety of pump-probe schemes. Using one of these, we record the linear absorption spectrum of a cryogenically cooled cluster without the use of a messenger “tag”. In another protocol, we reveal the spectra of individual H 2 O and D 2 O molecules embedded in each of the two possible binding sites in the iodide dihydrate, as well as the bands due to individual OH and OD groups in each of the four local binding environments. Finally, we demonstrate how temperature dependent isotopic scrambling among the spectral features can be used to monitor the onset of large amplitude motion, heretofore inferred from changes in the envelope of the OH stretching vibrational manifold. [ABSTRACT FROM AUTHOR]

The femtosecond-laser induced photodissociation of CH 3 Br adsorbed at sub-monolayer coverage on a solid surface was investigated by time-resolved pump-probe mass spectrometry. To tune the interaction of the CH 3 Br molecules with the substrate, an Mo(1 0 0) surface was covered with ultrathin insulating MgO layers of variable thickness. By gradually decreasing the magnesia layer thickness to the 2D limit the photodissociation dynamics observed by detection of the methyl fragment indicates an energetic lowering of the relevant methyl bromide excited states due to the increasing spatial proximity of the metallic support. Potential orientational effects of the methyl bromide adsorption geometry are also considered. [ABSTRACT FROM AUTHOR]

We characterize the 157 nm photodissociation of dichloromethane (CH 2 Cl 2 ) using photofragment translational spectroscopy, detecting the products with photoionization mass spectrometry. The major photodissociation products are Cl + CH 2 Cl and HCl + CHCl. Comparing the integrated ion signal at m/e = 35 (Cl + ) and m/e = 49 (CH 2 Cl + ) gives the partial photoionization cross section of CH 2 Cl to parent ion to be σ = 26.6 Mb at 13.7 eV. This value is a quantitative anchor point of the energy-dependent photoionization cross section. In recent work we used this result to quantify the product branching to HCO + CH 2 Cl in the photodissociation of 2-chloroacetaldehyde. [ABSTRACT FROM AUTHOR]

In this work, we compare the intensity ratio of symmetric to antisymmetric C O stretching vibrational transitions in CO 2 − and MCOO − (M = H, Ag and Bi) using photodissociation spectroscopy. We observe that this ratio depends strongly on the bonding partner M. We trace this behavior to a dynamic change in the charge distribution of the molecules during vibrational motion by comparing the derivatives of the dipole moment during vibrational motion calculated from a fixed-charge approximation, a charge distribution analysis, and the prediction of the infrared spectra of the ions under study. The calculations are based on density functional theory. [ABSTRACT FROM AUTHOR]

The real time photodissociation of chloroiodomethane (CH 2 ICl) in the first absorption band at 268 nm is reported in comparison with the well-known methyl iodide (CH 3 I) in order to investigate the halogen-atom substituent effect on the time-resolved photodynamics of halomethanes. Femtosecond velocity map imaging measurements in conjunction with resonance enhanced multiphoton ionization (REMPI) to detect the iodine fragments have been performed to obtain translational energy, angular distributions and the photodissociation reaction times. High level ab initio and on-the-fly trajectory calculations have been carried out to rationalize the experimental results in terms of the excited states involved and the dissociation mechanisms. [ABSTRACT FROM AUTHOR]

New ab initio surface hopping simulations of the excited state dynamics of CS 2 including spin-orbit coupling are compared to new experimental measurements using a multiphoton ionisation probe in a photoelectron spectroscopy experiment. The calculations highlight the importance of the triplet states even in the very early time dynamics of the dissociation process and allow us to unravel the signatures in the experimental spectrum, linking the observed changes to both electronic and nuclear degrees of freedom within the molecule. [ABSTRACT FROM AUTHOR]

The nonadiabatic tunneling-facilitated photodissociation of phenol is investigated using a reduced-dimensional quantum model on two ab initio-based coupled potential energy surfaces (PESs). Although dynamics occurs largely on the lower adiabat, the proximity to a conical intersection between the S 1 and S 2 states requires the inclusion of both the geometric phase (GP) and diagonal Born-Oppenheimer correction (DBOC). The lifetime of the lowest-lying vibronic state is computed using the diabatic and various adiabatic models. The GP and DBOC terms are found to be essential on one set of PESs, but have a small impact on the other. [ABSTRACT FROM AUTHOR]

State-resolved scattering distributions of the NO product in the photodissociation of CH 3 ONO were measured at 213 nm with resonantly-enhanced multiphoton ionization spectroscopy and ion-imaging. The spectra of the NO product displayed the vibrational population up to the v = 3 state having the rotational state-distribution with a Gaussian-like function. The scattering data of the NO ( v = 1) product indicate that the rotational excitation of the NO fragment and the translational energy release are fairly well compensated. This result is explained as being an outcome of the strong repulsion in the CH 3 O NO bond in the S 2 state. [ABSTRACT FROM AUTHOR]

The argon dimer cation is produced in a plasma generated by a laser spark in a supersonic expansion. The cold ions are mass selected and investigated by photodissociation at 355 nm, with velocity map imaging of the Ar + photofragment. Using the radius of the image, we determine the kinetic energy release and derive the ground state dissociation energy of Ar 2 + as D 0 ″ = 1.32 +0.03/−0.02 eV. Additionally, the angular distribution is described with β = 1.71–1.95, consistent with excitation of the parallel-type 2 Σ g + ← 2 Σ u + transition. [ABSTRACT FROM AUTHOR]

Photoexcitation of van der Waals (vdW) complex CH 3 I-O 2 has been studied with velocity map imaging of I atoms arising in photodissociation. A new scheme of resonance-enhanced multiphoton ionization of iodine atoms has been applied with simultaneous use of UV and VIS radiation. The measured kinetic energy of I( 2 P 3/2 ) atoms indicates photogeneration of precursor CH 3 I molecules via complex-specific channel with excitation energy expected for double spin-flip transition in complex CH 3 I-O 2 . The angular distribution for recoil directions of I( 2 P 3/2 ) atoms coming from vdW complexes also corresponds to that expected for double spin-flip transition. [ABSTRACT FROM AUTHOR]

Photodissociation pathways for 3,4-dichloro-1,2,5-thiadiazole was investigated in its ground state at various wavelengths in the UV region. The photolysis products were identified by the UV absorption and emission spectroscopy. Molecular chlorine (Cl 2 ) elimination was observed using absorption methods in the UV region. UV absorption and quantum calculation confirms the migration of chlorine atom and subsequent ring opening to form NC C(Cl 2 ) N S isomer. Multiphotonic excitation leading to the UV emission in the vicinity of 389 nm was observed due to the formation of CN(B 2 Σ + ) moiety. New UV absorption bands observed at ∼255 and ∼290 nm were assigned to the its isomer NC C(Cl 2 ) N S. [ABSTRACT FROM AUTHOR]

Vibrational structure of trifluoromethylthiobenzene (C 6 H 5 SCF 3 ) on the S 1 state has been investigated by resonance-enhanced two-photon ionization spectroscopy and nature of predissociation dynamics is inferred from homogeneously broadened spectral features. As C 6 H 5 SCF 3 adopts a nonplanar structure in both the S 0 and S 1 states, the effective adiabatic barrier generated by avoided crossing of optically-bright bound S 1 (ππ ∗ ) and dark-repulsive S 2 (πσ ∗ ) surfaces along the reaction coordinate is significantly lowered, giving the S 1 lifetime of ∼300 fs. This experiment demonstrates that the molecular structure spanned by the reactive flux near the curve-crossing region dictates reaction rate as well as nonadiabatic transition probability. [ABSTRACT FROM AUTHOR]

The photodissociation dynamics of iodocyclohexane in the A-band and C-state have been investigated by femtosecond time-resolved time-of-flight mass spectroscopy. Iodocyclohexane was pumped by 266 nm pulse to its A-band. The following dissociation dynamics is prompt and direct. The time it takes for the progression of the wave packet from the dissociative state to the dissociating asymptotic region is around 180 fs. The C-state was excited by 200 nm pump pulse and it has predissociative character with predissociation time of about 600 fs, which may have contributions from multiple vibrational modes. [ABSTRACT FROM AUTHOR]

We introduce a 1 + 1 probe of S( 1 D) at 216.9 nm through the (4s 3 S o ) state, and demonstrate it in one-color experiments to examine the photodissociation of OCS using DC slice imaging. As seen in previous work, the S( 1 D) image shows a bimodal distribution corresponding to two dissociation pathways of the parent molecule. The slice images are rotationally resolved across the entire product velocity profile. Separate two-color experiments allow us to determine that the probe is insensitive to orbital polarization in the sulfur atom under the conditions studied. [ABSTRACT FROM AUTHOR]

[Display omitted] • Photodissociation dynamics of astrophysically and combustion relevant xylene isomers C 6 H 4 (CH 3) 2 at 157 nm. • Formation of 'hot' tolyl radicals via C-C bond rupture of xylene reactants. • The presence of tolyl radicals in the interstellar medium as a precursor to methylated polyreactions with vinylacetylene (C 4 H 4). We investigated the photodissociation dynamics of three xylene isomers C 6 H 4 (CH 3) 2 at 157 nm. The center-of-mass translational energy distributions of C 7 H 7 radicals were found to peak at 26 kJ mol−1. Although the ionization energy of the C 7 H 7 tolyl fragment exceeds the energy of a 157 nm photon, C 7 H 7 + was observed as a result of the photoionization of vibrationally 'hot' tolyl (C 7 H 7) radicals and/or two-photon ionization. The formation of rovibrationally excited tolyl fragments was discussed. Our experiments suggest the presence of tolyl radicals in the interstellar medium as a precursor to methylated polycyclic aromatic hydrocarbons upon reaction with vinylacetylene (C 4 H 4). [ABSTRACT FROM AUTHOR]

[Display omitted] • Methylidine (CH) was generated by multiphoton photodissociation of CHCl 3 and CHBr 3. • CH(X2Π) has been detected with laser-induced fluorescence via the A2Δ − X2Π transition. • The rate coefficients for the reactions of CH with CHCl 3 and CHBr 3 were determined. • CH can readily insert into C − Cl and C − Br bonds in halomethanes. • Evans − Polanyi principle accounts for the relation between k (CH + CHX 3) and Δ r H °. Methylidyne (CH) was generated in the ultraviolet multiphoton photolysis of CHCl 3 and CHBr 3 and detected with laser-induced fluorescence (LIF) via the A2Δ − X2Π (0,0) transition. The time-resolved LIF intensity recorded at varying pressures of CHCl 3 and CHBr 3 has given the overall rate coefficients for the reactions of CH with CHCl 3 and CHBr 3. The near gas kinetic rates indicate that CH inserts into the C − Cl and C − Br bonds. The correlation between the rate coefficients for the CH + CH n X 4− n (X = F, Cl, and Br) reactions and the heats of reactions for H-, Cl-, Br-elimination is elucidated by the Evans − Polanyi principle. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Randomly oriented HOD molecules are vibrationally excited via the dynamic Stark effect. • Simple linear temporal chirp of a UV pulse can control the selectivity of bond breaking in HOD. • In order to narrow the gap between theory and experiment, the feasibility of the proposed control scheme is emphasized. Abstract The VUV photodissociation dynamics of HOD in the first ( A ∼ -state) absorption band following a non-resonant impulsive vibrational excitation is studied theoretically. We show that a change in the linear temporal chirp of a VUV pulse with a fixed frequency distribution leads to control of the branching ratio (H + OD)/(D + OH) between the two fragmentation channels. [ABSTRACT FROM AUTHOR]

[Display omitted] • The ion-imaging study was performed for photodissociation of dimethylamine. • Two kinetic energy components of the methyl radical product were measured. • The calculation revealed the potential energy curves for N–CH 3 and N–H dissociations. State-resolved ion-imaging of the CH 3 product of dimethylamine photolysis in the 3s and 3p Rydberg bands (200–235 nm) revealed bimodal CH 3 velocity distributions with a fast portion disappearing at the longer photolysis wavelength. The fast component is assigned to direct dissociation based on the calculated potential energy curves. The slow component is assigned to indirect dissociation via N–H channel conical intersection with subsequent CH 3 dissociation. The origin of the threshold wavelength near 225 nm was attributed to the N–CH 3 bond rupture energy barrier on the S 1 (3s) state, implying an increasing contribution of direct dissociation at the shorter photolysis wavelengths. [ABSTRACT FROM AUTHOR]

The absolute absorption cross sections of (CH 3 ) 2 COO under a jet-cooled condition were measured via laser depletion to be (1.32 ± 0.10) × 10 −17 cm 2 molecule −1 at 308 nm and (9.6 ± 0.8) × 10 −18 cm 2 molecule −1 at 352 nm. The peak UV cross section is estimated to be (1.75 ± 0.14) × 10 −17 cm 2 molecule −1 at 330 nm, according to the UV spectrum of (CH 3 ) 2 COO (Huang et al., 2015) scaled to the absolute cross section at 308 nm. [ABSTRACT FROM AUTHOR]

Femtosecond time-resolved transient grating (TG) technique was employed to get insight into the photodissociation mechanism of liquid nitromethane (NM). Broadband white-light continuum was introduced as the probe to observe the evolution of electronic excited states of NM molecules and the formation of photodissociation products simultaneously. The reaction channel of liquid NM under 266 nm excitation was obtained that NM molecules in excited state S 2 relax through two channels: about 73% relax to low lying S 1 state through S 2 /S 1 internal conversion with a time constant of 0.24 ps and then go back to the ground state through S 1 /S 0 internal conversion; the other 27% will dissociate with a time constant of 2.56 ps. NO 2 was found to be one of the products from the experimental TG spectra, which confirmed that C–N bond rupture was the primary dissociation channel of liquid NM. [ABSTRACT FROM AUTHOR]

We have applied the technique of picosecond laser spectroscopy to study the photodissociation of nitrobenzene at room temperature and 100 mTorr. Three different photolysis pulses, λ 2 = 250, 266, and 280 nm, with a duration of 20–25 ps, were used. The NO photofragment was detected via LIF between λ 1 = 220 and 250 nm. The profile of rotational population distribution shows a dependency on the photolysis wavelength and the delay time. The observed rotational population distributions are non-Boltzmann and bimodal for v ″ = 0, 1, and 2. [ABSTRACT FROM AUTHOR]

Product yields were measured in the 296 K photolysis of CF 3 C(O)Cl at 193, 248, 254, and 280 nm. Br 2 was used as a radical scavenger to convert the primary CF 3 and CF 3 CO radical photofragments into stable bromides, CF 3 Br and CF 3 C(O)Br, which were quantified along with CO and CF 2 O using infrared absorption. The stabilized CF 3 CO radical yield increased with increasing photolysis wavelength from <0.007 at 193 nm to 0.95 − 0.10 + 0.05 at 280 nm. An upper-limit for the ClCO radical yield was estimated to be <0.004 at all wavelengths. The CF 3 Cl quantum yield was determined to be <0.001 at all wavelengths. [ABSTRACT FROM AUTHOR]

We obtain the ultraviolet photodissociation spectrum of adenine complexes with K + ion stored in a cold ion trap. The spectrum near the origin band of the S 0 –S 1 transition exhibits well-resolved vibronic bands, all of which are assigned from a single isomer by UV–UV hole-burning (HB) spectroscopy. Comparing the spectrum with theoretical spectra, we determine the structure of the isomer, where K + is bound not to 9H-adenine (A9) but to 7H-adenine (A7). We suggest that K + A7 ions are formed in solution through tautomerization, for which the energy barrier varies greatly depending on the binding site of the K + ion on A9. [ABSTRACT FROM AUTHOR]

We demonstrate that broadband impulsive stimulated Raman scattering with transient grating experimental geometry is capable of recording vibrational spectra in time and frequency domains to reveal the dissociation mechanism of liquid CH 3 I. The repulsive 3 Q 0 potential energy surface is modified to a quasi-bound surface in the liquid CH 3 I due to the solvent cage, making the wave packets to get trapped. A small portion of the wave packet passes through the solvent cage, resulting in the C I bond breakage with the product I 2 . This work provides a first glimpse of immense potential of BB-ISRS in studying photodissociation dynamics in liquids. [ABSTRACT FROM AUTHOR]

We recorded the IR spectra of C 2 H 4 + trapped in solid Ar through electron bombardment of a mixture of ethylene and Ar during matrix deposition. The four most intense lines of C 2 H 4 + were observed and assigned according to comparison with the literature data for ethylene with solid Ne and the predicted vibrational anharmonic wavenumbers. Experiments involving further UV irradiations of the matrix samples were performed in the region 345–225 nm. Upon UV radiation, lines of C 2 H 4 + decreased and lines corresponding to C 2 H 4 , C 2 H 2 , and C 2 H 3 increased, indicating that the photodissociation and photo-assisted neutralization of C 2 H 4 + in the matrix may occur simultaneously. [ABSTRACT FROM AUTHOR]

We have observed fragment-ion images by ultraviolet photodissociation of Mg + FCH 3 complex using a reflectron time-of-flight mass spectrometer coupled with an imaging detector. Fourth harmonic of a Nd:YAG laser was used for excitation of Mg + FCH 3 from 1 2 A 1 to 2 2 A 1 state, which has a main character corresponding to Mg + 2 P ← 2 S transition. We observed images of MgF + fragments and determined the kinetic energy release and angular distributions. Among the calculated potential energy curves of Mg + FCH 3 along F C bond length, the 2 2 A 1 state was repulsive. The observed energy and angular distributions were consistent with fast MgF + formation on the repulsive potential energy curve. [ABSTRACT FROM AUTHOR]

The MO ( CO ) 5 + (M = Sc, Y, La and Ce) complexes are generated and analyzed using an infrared photodissociation spectrometer. Their C O stretching frequencies are determined to be 2210 cm −1 , 2206 cm −1 , 2198 cm −1 and 2196 cm −1 for M = Sc, Y, La and Ce, respectively. The simulated spectra from DFT calculations are compared with the experimental results, indicating MO ( CO ) 5 + (M = Sc, Y, La and Ce) are or very close to pentagonal pyramidal structures with C 5V symmetry. The comparisons of these complexes with other metal carbonyls help to elucidate the characteristics of CO coordination in various metal species. [ABSTRACT FROM AUTHOR]

Vacuum ultraviolet (VUV) photodissociation of CH 3 OH and CH 3 OD at 121.6 nm was studied using high- n Rydberg atom time-of-flight (HRTOF) technique. The H-atom product TOF spectrum of CH 3 OH and D-atom spectrum of CH 3 OD have bimodal distributions. O–H (CH 3 O + H(D)) and C–H (CH 2 OH(D) + H) dissociations contribute to the fast component. The slow component corresponds to CH 2 O + H + H(D) production, mainly from three-body photodissociation, plus small contributions from secondary dissociation of CH 3 O and CH 2 OH(D). The CH 2 O + H + H formation is the major photodissociation pathway, with a branching ratio of (CH 2 O + H + H):(CH 3 O + H):(CH 2 OH + H) ≈ 1:0.25:0.15. [ABSTRACT FROM AUTHOR]

To explore the dynamic mechanism of the hydroxyl radical generation from the ozone-water complex and its atmospheric implications, the intrinsic reaction coordinate computations and ab initio molecular dynamic simulations were used to map the minimum energy profiles of O3 and O3-H2O complex photo-dissociation and inspect photo-dissociation feasibility for different complex conformers. The stable trans isomer possesses a small portion in seven coexistent O3-H2O complex conformers, 70% of which is the unique source to produce OH radicals in SPP(...1A', ¹ππ*) state. The quantum yield of atmospheric hydroxyl radical through the ozone-water complex photolysis is much lower than the previous expectation. [ABSTRACT FROM AUTHOR]

Highlights: [•] We present the first result on the photo-fragmentation of the hexa-peri-hexabenzocoronene (HBC) cation –C42H18 +–. [•] Both stepwise dehydrogenation and C2/C2H2 loss pathways are identified as relevant photodissociation routes. [•] Our conclusions support the idea that graphene sheets, cages, and bare carbon rings may be abundant in space. [ABSTRACT FROM AUTHOR]

Highlights: [•] A long-standing problem in the photodissociation of ICl has been resolved. [•] Absorption intensities to 0+(III) and 0+(IV) have a comparable magnitude. [•] Quantum interference between the dissociation paths on 0+(III) and 0+(IV) was a key. [•] Branching ratios and beta parameters are in agreement between experiment and theory. [•] An interpretation based on a time-dependent perturbation treatment is given. [ABSTRACT FROM AUTHOR]

Highlights: [•] OH radicals detected from organic hydroperoxide photolysis at 266, 291, 331, 362, and 377nm. [•] Translational energy release higher for ethyl versus tert-butyl hydroperoxide. [•] More rotation in OH from tert-butyl versus ethyl hydroperoxide at 266, 291, 331nm. [•] Absorption cross sections may reflect torsion promoting long-wavelength absorption. [ABSTRACT FROM AUTHOR]

Highlights: [•] Low translational energy release to I∗ (2 P 1/2) photofragments. [•] Impulsive recoil of I∗ and CH2I products. [•] Anisotropic angular distribution indicative of electronic state mixing. [•] High internal excitation of CH2I fragments likely carried into CH2OO intermediates. [ABSTRACT FROM AUTHOR]

Abstract: The production of Cl atoms in the laser flash photolysis of ClOOCl at 308nm has been investigated by time-resolved atomic resonance fluorescence at 235K. A value of ϕ =1.03±0.12 has been obtained for the primary quantum yield based on an absorption cross section ratio σ 245/σ 308 =22 for ClOOCl at 245 and 308nm. [Copyright &y& Elsevier]

Highlights: [•] Methyl-cyclopentanone ionization/dissociation is studied in strong fs laser fields. [•] Mass spectra are analyzed to understand the effects of methyl substitution. [•] Generalized-KFR theory calculations are performed for the photoionization mechanism. [•] Ab initio/RRKM calculations are used to unravel the photodissociation patterns. [ABSTRACT FROM AUTHOR]

[Display omitted] • Spin-polarized molecules from IR-excitation and photodissociation of molecular beams. • Projected production rates much higher than conventional spin-separation methods. • Macroscopic spin-polarized molecules enhance NMR signals and fusion cross sections. Pure, highly nuclear-spin-polarized molecules have only been produced with molecular beam-separation methods, with production rates up to ∼ 3 × 10 12 s−1. Here, we propose the production of spin-polarized molecular photofragments from the IR-excitation and photodissociation of molecular beams, with production rates approaching the tabletop-IR-laser photon fluxes of 10 21 s−1. We give details on the production of spin-polarized molecular hydrogen and water isotopes, from formaldehyde and formic acid beams, respectively. Macroscopic quantities of these molecules are important for NMR signal enhancement, and for the needs of a nuclear fusion reactor, to increase the D-T or D-3He unpolarized nuclear fusion cross section by ∼ 50 %. [ABSTRACT FROM AUTHOR]

Abstract: We report on the light induced spin crossover dynamics of [Fe(2 CH3-phen)3]2+ complex in solution. The excitation of the complex by pulses centered at λ =500nm along the metal to ligand charge transfer absorption band indicates a selective excitation of the LS state. The excitation of the complex by pulses centered at λ =330nm or λ =335nm reveals an increase of the LS state population and a photo-bleaching of the HS state population that is associated to a transient photo-dissociation. A method that makes it possible to deduce the kinetics of both the HS→LS state and LS→HS state is proposed. [Copyright &y& Elsevier]

Abstract: The photodissociation dynamics of nitromethane (CH3NO2), following photoabsorption at 213nm in the π∗ ←π transition, has been studied using ion-imaging. The state-resolved velocity and angular distributions were measured for the CH3, NO, and O atom fragments. The CH3 velocity distribution consisted of two peaks with different angular distributions; the slow and fast components showed isotropic and anisotropic distributions, respectively. The NO and O fragments also showed slow components with isotropic angular distributions. The results observed consistently indicate that these slow photofragments were possibly produced by the concerted three-body dissociation channel. [Copyright &y& Elsevier]