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Smog chambers interfaced with in situ FT-IR detection were used to investigate the kinetics and mechanisms of the Cl atom, OH radical, and O3 initiated oxidation of (Z)- and (E)-1,2-dichloroethene (CHCl＝CHCl) under atmospheric conditions. Relative and absolute rate methods were used to measure k(Cl + (Z)-CHCl＝CHCl) = (8.80 ± 1.75) × 10−11, k(Cl + (E)-CHCl＝CHCl) = (8.51 ± 1.69) × 10−11, k(OH + (Z)-CHCl＝CHCl) = (2.02 ± 0.43) × 10−12, k(OH + (E)-CHCl＝CHCl) = (1.94 ± 0.43) × 10−12, k(O3 + (Z)-CHCl＝CHCl) = (4.50 ± 0.45) × 10−21, and k(O3 + (E)-CHCl＝CHCl) = (1.02 ± 0.10) × 10−19 cm3 molecule−1 s−1 in 700 Torr of N2/air diluent at 298 ± 2 K. Pressure dependencies for the Cl atom reaction kinetics were observed for both isomers, consistent with isomerization occurring via Cl atom elimination from the chemically activated CHCl–CHCl–Cl adduct. The observed products from Cl initiated oxidation were HC(O)Cl (117–133%), CHCl2CHO (29–30%), and the corresponding CHCl＝CHCl isomer (11–20%). OH radical initiated oxidation gives HC(O)Cl as a major product. For reaction of OH with (E)-CHCl＝CHCl, (Z)-CHCl＝CHCl was also observed as a product. A significant chlorine atom elimination channel was observed experimentally (HCl yield) and supported by computational results. Photochemical ozone creation potentials of 12 and 11 were estimated for (Z)- and (E)-CHCl＝CHCl, respectively. Finally, an empirical kinetic relationship is explored for the addition of OH radicals or Cl atoms to small alkenes. The results are discussed in the context of the atmospheric chemistry of (Z)- and (E)-CHCl＝CHCl. [ABSTRACT FROM AUTHOR]

Long path length FTIR-smog chamber techniques were used to study the title reactions in 700 Torr of N2, oxygen or air diluent at 296 ± 2 K. Values of k(Cl + CF3CN) = (2.43 ± 0.33) × 10−15 and k(OH + CF3CN) = (4.61 ± 0.34) × 10−15 cm3 molecule−1 s−1 were measured. There was no discernible reaction of CF3CN with O3 and an upper limit of k(O3 + CF3CN) ≤ 7.9 × 10−24 cm3 molecule−1 s−1 was established. The IR spectra of CF3CN and CF3CF2CN are reported. The atmospheric lifetime of CF3CN is determined by the reaction with OH and is approximately 6.9 years. Reaction of CF3CN with Cl atoms in a chamber study gives (Z-) and/or (E-) CF3CCl＝NCl and CF3C(O)Cl as major primary products. Under environmental conditions, the OH radical initiated oxidation gives COF2 in a yield of (96 ± 8)%. The global warming potential for CF3CN is estimated as 1030 for a 100 year time horizon. [ABSTRACT FROM AUTHOR]

We have characterized the various pathways for OH radical (OH˙) induced decomposition of tert-butyl methyl ether (MTBE) and found an oxidative pathway that leads to complete degradation under the prerequisite that OH radicals are present in excess. A simple polarizable continuum model is used to predict the behavior in an aqueous medium and the behavior is unchanged compared to that in the gas phase. The computational study has also revealed some of the fundamental aspects of hydrogen transfer from asymmetric ethers; the ˙OH assisted hydrogen abstraction has a barrier when the reaction takes place at a distance from the heteroatom, that is, at the tert-butyl group, whereas hydrogen abstraction from the methyl group proceeds without a barrier. The addition of ˙OH to (CH3)3COCH2˙ also proceeds without a barrier, and so does hydrogen abstraction from the resulting adduct ((CH3)3COCH2OH) to form (CH3)3COCH(OH)˙. However, a barrier is yet again found in the hydrogen abstraction from the latter to form (CH3)3COCH＝O and yet again in the formation of the formyl radical (CH3)3COC＝O˙ by hydrogen abstraction. The latter is the last step before the final stage of complete oxidation of MTBE to form CO2. [ABSTRACT FROM AUTHOR]

Symmetry effects in internal conversion are studied by means of two isomeric cyclic tertiary aliphatic amines in a velocity map imaging (VMI) experiment on the femtosecond timescale. It is demonstrated that there is a delicate structural dependence on when coherence is preserved after the transition between the 3p and 3s Rydberg states. N-Methyl morpholine (NMM) shows unambiguous preserved coherence, consistent with previous work, which is decidedly switched off by the repositioning of oxygen within the ring. From the differences in these dynamics, and an examination of the potential energy surface following the normal modes of vibration, it becomes clear that there is a striking dependence on atom substitution, which manifests itself in the permitted modes of vibration that take the system out of the Franck–Condon region through to the 3s minimum. It is shown that the non Fermi-like behaviour of NMM is due to a conical intersection (CI) between the 3px and 3s states lying directly along the symmetry allowed path of steepest descent out of the Franck–Condon region. NMI, where the symmetry has been changed, is shown to undergo internal conversion in a more Fermi-like manner as the energy spreads through the available modes ergodically. [ABSTRACT FROM AUTHOR]

The chemical mechanisms of the OH radical, Cl-atom and O3 initiated oxidation of (Z)-CF3CH=CHCl were studied at 296 ± 1 K in 10–700 Torr air of N2/O2 diluent. Cl atoms add to the ⧸⧹C=C⧸⧹ double bond: 12 ± 5% to the terminal carbon and 85 ± 5% to the central carbon. In 700 Torr of air the products are CF3CHClCHO, HCOCl, CF3COCl, CF3CHO, (E)-CF3CH=CHCl, CF3C(O)CHCl2, and CF3CHClCOCl. The yield of (E) isomer was dependent on total pressure, but independent of O2 partial pressure; consistent with isomerization occurring via Cl atom elimination from the chemically activated rather than the thermalized CF3CHCHCl–Cl adduct. The rate constant for (Z)-CF3CH=CHCl + Cl was measured at low pressure (10–15 Torr) and found to be indistinguishable from that determined at 700 Torr total pressure, whereas the low pressure rate constant for (E)-CF3CH=CHCl was 36% smaller. G4MP2 ab initio calculations showed that the (E) isomer is 1.2 kcal mol−1 more stable than the (Z) isomer. Cl atom elimination from the adduct will preferentially form the (E) isomer and hence the rate of CF3CH=CHCl loss will be more sensitive to pressure for the (Z) than the (E) isomer. Reaction of (Z)-CF3CH=CHCl with OH radicals gives CF3CHO, HCOCl, (E)-CF3CH=CHCl, and HCl. A significant chlorine atom elimination channel was observed experimentally, and supported by computational results. The oxidation products of the reaction of O3 with (Z)- and (E)-CF3CH=CHCl were determined with no evidence of isomerization. The results are discussed with respect to the atmospheric chemistry and environmental impact of (Z)- and (E)-CF3CH=CHCl. [ABSTRACT FROM AUTHOR]

Bithiophenes serve as model systems for larger polythiophenes used in solar cell applications and molecular electronics. We report a study of ultrafast dynamics of two bithiophene systems measured with femtosecond time-resolved photoelectron spectroscopy, and show that their intersystem crossing takes place within the first few picoseconds after excitation, in line with previous studies. We show that the intersystem crossing rate can be explained in terms of arguments based on symmetry of the S1 minimum energy geometry, which depends on the specific conformation of bithiophene. Furthermore, this work shows that the minor cis-conformer contributes to an even higher intersystem crossing rate than the major trans conformer. The work presented here can provide guiding principles towards the design of solar cell components with even faster formation of long-lived excited states for solar energy harvesting. [ABSTRACT FROM AUTHOR]

The atmospheric fates of Z- and E-CF3CH=CHCF3 have been studied, investigating the kinetics and the products of the reactions of the two compounds with Cl atoms, OH radicals, OD radicals, and O3. FTIR smog chamber experiments measured: k(Cl + Z-CF3CH=CHCF3) = (2.59 ± 0.47) × 10−11, k(Cl + E-CF3CH=CHCF3) = (1.36 ± 0.27) × 10−11, k(OH + Z-CF3CH=CHCF3) = (4.21 ± 0.62) × 10−13, k(OH + E-CF3CH=CHCF3) = (1.72 ± 0.42) × 10−13, k(OD + Z-CF3CH=CHCF3) = (6.94 ± 1.25) × 10−13, k(OD + E-CF3CH=CHCF3) = (5.61 ± 0.98) × 10−13, k(O3 + Z-CF3CH=CHCF3) = (6.25 ± 0.70) × 10−22, and k(O3 + E-CF3CH=CHCF3) = (4.14 ± 0.42) × 10−22 cm3 molecule−1 s−1 in 700 Torr of air/N2/O2 diluents at 296 ± 2 K. E-CF3CH=CHCF3 reacts with Cl atoms to give CF3CHClC(O)CF3 in a yield indistinguishable from 100%. Z-CF3CH=CHCF3 reacts with Cl atoms to give (95 ± 10)% CF3CHClC(O)CF3 and (7 ± 1)% E-CF3CH=CHCF3. CF3CHClC(O)CF3 reacts with Cl atoms to give the secondary product CF3C(O)Cl in a yield indistinguishable from 100%, with the observed co-products C(O)F2 and CF3O3CF3. The main atmospheric fate for Z- and E-CF3CH=CHCF3 is reaction with OH radicals. The atmospheric lifetimes of Z- and E-CF3CH=CHCF3 are estimated as 27 and 67 days, respectively. IR absorption cross sections are reported and the global warming potentials (GWPs) of Z- and E-CF3CH=CHCF3 for the 100 year time horizon are calculated to be GWP100 = 2 and 7, respectively. This study provides a comprehensive description of the atmospheric fate and impact of Z- and E-CF3CH=CHCF3. [ABSTRACT FROM AUTHOR]

Correction for 'Atmospheric chemistry of CF3CN: kinetics and products of reaction with OH radicals, Cl atoms and O3' by Mads Peter Sulbaek Andersen et al., Phys. Chem. Chem. Phys., 2022, 24, 2638–2645, https://doi.org/10.1039/D1CP05288H. [ABSTRACT FROM AUTHOR]

Correction for 'Atmospheric chemistry of (Z)- and (E)-1,2-dichloroethene: kinetics and mechanisms of the reactions with Cl atoms, OH radicals, and O3' by Mads P. Sulbaek Andersen et al., Phys. Chem. Chem. Phys., 2022, 24, 7356–7373, https://doi.org/10.1039/D1CP04877E. [ABSTRACT FROM AUTHOR]

We have investigated the electronic relaxation dynamics of gas-phase piperidine (a secondary aliphatic amine) using time-resolved photoelectron imaging. Following 200 nm excitation, spectrally sharp and highly anisotropic photoelectron data reveal ultrafast (60 fs) internal conversion between the initially excited 3px Rydberg state and the lower-lying 3s Rydberg state, mediated by the evolution of nσ* valence character along the 3px N–C bond. This behaviour is in good agreement with previously reported findings for several tertiary aliphatic amines. In contrast to the these systems, however, much broader photoelectron signals exhibiting only very small angular anisotropy and two distinct decay timescales (180 fs and 1.7 ps) were also observed. As confirmed by our supporting calculations, this is attributable to nσ* valence character now evolving along the N–H stretching coordinate within the 3s Rydberg state as the molecule starts dissociating to yield H atom photoproducts in conjunction with ground state piperidinyl radicals. By analogy with systems such as ammonia and morpholine, we conclude this event may occur either promptly or, alternatively, via a “frustrated” process where the system repeatedly traverses the upper cone of a conical intersection with the ground state until the required region of phase space is sampled to facilitate non-adiabatic population transfer. Our findings reveal the role of several different nuclear coordinate motions in driving stepwise internal conversion across multiple potential energy surfaces and the distinct photoionization signatures that are associated with these processes. [ABSTRACT FROM AUTHOR]

The non-adiabatic relaxation dynamics of the tertiary cage-amine azabicyclo[2.2.2]octane (ABCO, also known as quinuclidine) have been investigated following 3p Rydberg excitation at 201 nm using femtosecond time-resolved photoelectron imaging (TRPEI). The aim of the study was to investigate the influence of the rigid and symmetric cage structure found in ABCO on the general non-adiabatic relaxation processes commonly seen in other tertiary aliphatic amines (TAAs). Our data is compared with TRPEI results very recently obtained for several structurally less rigid TAA systems [J. O. F. Thompson et al., Chem. Sci., 2016, 7, 1826–1839] and helps to confirm many of the previously reported findings. The experimental results for ABCO in the short-time (＜1 ps) regime strongly support earlier conclusions suggesting that planarization about the N-atom is not a prerequisite for efficient 3p–3s internal conversion. Additionally, individual photoelectron peaks within our ABCO data show no temporal shifts in energy. As confirmed by our supporting quantum mechanical calculations, this demonstrates that neither internal conversion within the 3p manifold or significant conformational re-organization are possible in the ABCO system. This result therefore lends strong additional support to the active presence of such dynamical effects in other, less conformationally restricted TAA species, where photoelectron peak shifts are commonly observed. Finally, the extremely long (＞1 ns) 3s Rydberg state lifetime seen in ABCO (relative to other TAA systems at similar excitation energies) serves to illustrate the large influence of symmetry and conformational rigidity on intramolecular vibrational redistribution processes previously implicated in mediating this aspect of the overall relaxation dynamics. [ABSTRACT FROM AUTHOR]

Smog chambers interfaced with in situ FT-IR detection were used to investigate the kinetics and mechanisms of the Cl atom, OH radical, and O 3 initiated oxidation of ( Z )- and ( E )-1,2-dichloroethene (CHClCHCl) under atmospheric conditions. Relative and absolute rate methods were used to measure k (Cl + ( Z )-CHClCHCl) = (8.80 ± 1.75) × 10 -11 , k (Cl + ( E )-CHClCHCl) = (8.51 ± 1.69) × 10 -11 , k (OH + ( Z )-CHClCHCl) = (2.02 ± 0.43) × 10 -12 , k (OH + ( E )-CHClCHCl) = (1.94 ± 0.43) × 10 -12 , k (O 3 + ( Z )-CHClCHCl) = (4.50 ± 0.45) × 10 -21 , and k (O 3 + ( E )-CHClCHCl) = (1.02 ± 0.10) × 10 -19 cm 3 molecule -1 s -1 in 700 Torr of N 2 /air diluent at 298 ± 2 K. Pressure dependencies for the Cl atom reaction kinetics were observed for both isomers, consistent with isomerization occurring via Cl atom elimination from the chemically activated CHCl-CHCl-Cl adduct. The observed products from Cl initiated oxidation were HC(O)Cl (117-133%), CHCl 2 CHO (29-30%), and the corresponding CHClCHCl isomer (11-20%). OH radical initiated oxidation gives HC(O)Cl as a major product. For reaction of OH with ( E )-CHClCHCl, ( Z )-CHClCHCl was also observed as a product. A significant chlorine atom elimination channel was observed experimentally (HCl yield) and supported by computational results. Photochemical ozone creation potentials of 12 and 11 were estimated for ( Z )- and ( E )-CHClCHCl, respectively. Finally, an empirical kinetic relationship is explored for the addition of OH radicals or Cl atoms to small alkenes. The results are discussed in the context of the atmospheric chemistry of ( Z )- and ( E )-CHClCHCl.

Long path length FTIR-smog chamber techniques were used to study the title reactions in 700 Torr of N 2 , oxygen or air diluent at 296 ± 2 K. Values of k (Cl + CF 3 CN) = (2.43 ± 0.33) × 10 -15 and k (OH + CF 3 CN) = (4.61 ± 0.34) × 10 -15 cm 3 molecule -1 s -1 were measured. There was no discernible reaction of CF 3 CN with O 3 and an upper limit of k (O 3 + CF 3 CN) ≤ 7.9 × 10 -24 cm 3 molecule -1 s -1 was established. The IR spectra of CF 3 CN and CF 3 CF 2 CN are reported. The atmospheric lifetime of CF 3 CN is determined by the reaction with OH and is approximately 6.9 years. Reaction of CF 3 CN with Cl atoms in a chamber study gives ( Z -) and/or ( E -) CF 3 CClNCl and CF 3 C(O)Cl as major primary products. Under environmental conditions, the OH radical initiated oxidation gives COF 2 in a yield of (96 ± 8)%. The global warming potential for CF 3 CN is estimated as 1030 for a 100 year time horizon.

The chemical mechanisms of the OH radical, Cl-atom and O3 initiated oxidation of (Z)-CF3CH[double bond, length as m-dash]CHCl were studied at 296 ± 1 K in 10-700 Torr air of N2/O2 diluent. Cl atoms add to the [double bond splayed left]C[double bond, length as m-dash]C[double bond splayed right] double bond: 12 ± 5% to the terminal carbon and 85 ± 5% to the central carbon. In 700 Torr of air the products are CF3CHClCHO, HCOCl, CF3COCl, CF3CHO, (E)-CF3CH[double bond, length as m-dash]CHCl, CF3C(O)CHCl2, and CF3CHClCOCl. The yield of (E) isomer was dependent on total pressure, but independent of O2 partial pressure; consistent with isomerization occurring via Cl atom elimination from the chemically activated rather than the thermalized CF3CHCHCl-Cl adduct. The rate constant for (Z)-CF3CH[double bond, length as m-dash]CHCl + Cl was measured at low pressure (10-15 Torr) and found to be indistinguishable from that determined at 700 Torr total pressure, whereas the low pressure rate constant for (E)-CF3CH[double bond, length as m-dash]CHCl was 36% smaller. G4MP2 ab initio calculations showed that the (E) isomer is 1.2 kcal mol-1 more stable than the (Z) isomer. Cl atom elimination from the adduct will preferentially form the (E) isomer and hence the rate of CF3CH[double bond, length as m-dash]CHCl loss will be more sensitive to pressure for the (Z) than the (E) isomer. Reaction of (Z)-CF3CH[double bond, length as m-dash]CHCl with OH radicals gives CF3CHO, HCOCl, (E)-CF3CH[double bond, length as m-dash]CHCl, and HCl. A significant chlorine atom elimination channel was observed experimentally, and supported by computational results. The oxidation products of the reaction of O3 with (Z)- and (E)-CF3CH[double bond, length as m-dash]CHCl were determined with no evidence of isomerization. The results are discussed with respect to the atmospheric chemistry and environmental impact of (Z)- and (E)-CF3CH[double bond, length as m-dash]CHCl.

The atmospheric fates of Z- and E-CF 3 CH[double bond, length as m-dash]CHCF 3 have been studied, investigating the kinetics and the products of the reactions of the two compounds with Cl atoms, OH radicals, OD radicals, and O 3 . FTIR smog chamber experiments measured: k(Cl + Z-CF 3 CH[double bond, length as m-dash]CHCF 3 ) = (2.59 ± 0.47) × 10 -11 , k(Cl + E-CF 3 CH[double bond, length as m-dash]CHCF 3 ) = (1.36 ± 0.27) × 10 -11 , k(OH + Z-CF 3 CH[double bond, length as m-dash]CHCF 3 ) = (4.21 ± 0.62) × 10 -13 , k(OH + E-CF 3 CH[double bond, length as m-dash]CHCF 3 ) = (1.72 ± 0.42) × 10 -13 , k(OD + Z-CF 3 CH[double bond, length as m-dash]CHCF 3 ) = (6.94 ± 1.25) × 10 -13 , k(OD + E-CF 3 CH[double bond, length as m-dash]CHCF 3 ) = (5.61 ± 0.98) × 10 -13 , k(O 3 + Z-CF 3 CH[double bond, length as m-dash]CHCF 3 ) = (6.25 ± 0.70) × 10 -22 , and k(O 3 + E-CF 3 CH[double bond, length as m-dash]CHCF 3 ) = (4.14 ± 0.42) × 10 -22 cm 3 molecule -1 s -1 in 700 Torr of air/N 2 /O 2 diluents at 296 ± 2 K. E-CF 3 CH[double bond, length as m-dash]CHCF 3 reacts with Cl atoms to give CF 3 CHClC(O)CF 3 in a yield indistinguishable from 100%. Z-CF 3 CH[double bond, length as m-dash]CHCF 3 reacts with Cl atoms to give (95 ± 10)% CF 3 CHClC(O)CF 3 and (7 ± 1)% E-CF 3 CH[double bond, length as m-dash]CHCF 3 . CF 3 CHClC(O)CF 3 reacts with Cl atoms to give the secondary product CF 3 C(O)Cl in a yield indistinguishable from 100%, with the observed co-products C(O)F 2 and CF 3 O 3 CF 3 . The main atmospheric fate for Z- and E-CF 3 CH[double bond, length as m-dash]CHCF 3 is reaction with OH radicals. The atmospheric lifetimes of Z- and E-CF 3 CH[double bond, length as m-dash]CHCF 3 are estimated as 27 and 67 days, respectively. IR absorption cross sections are reported and the global warming potentials (GWPs) of Z- and E-CF 3 CH[double bond, length as m-dash]CHCF 3 for the 100 year time horizon are calculated to be GWP 100 = 2 and 7, respectively. This study provides a comprehensive description of the atmospheric fate and impact of Z- and E-CF 3 CH[double bond, length as m-dash]CHCF 3 .

The Paternò-Büchi (PB) reaction between an excited carbonyl compound and an alkene has been widely studied, but so far little is known about the excited-state dynamics of the reaction. In this investigation, we used a compound in which a formyl and a vinyl group are attached to a [2.2]paracyclophane in order to obtain a model system in pre-reactive conformation for the PB reaction. We studied the excited-state dynamics of the isolated molecule in a molecular beam using femtosecond time-resolved photoelectron spectroscopy and ab initio calculations. The results show that inter-system crossing within two picoseconds competes efficiently with the reaction in the singlet manifold. Thus, the PB reaction in this model system takes place in the triplet state on a time scale of nanoseconds. This result stresses the importance of triplet states in the excited-state pathway of the PB reaction involving aromatic carbonyl compounds, even in situations in which the reacting moieties are in immediate vicinity.

We have performed ab initio calculations to examine the potential energy along the normal modes of ground-state HCHO and along the reaction coordinates for loss of H2 and atomic hydrogen, respectively. This exploration showed that there are no specific features that will lead to reaction on the excited-state surfaces for excitations that are relevant to the troposphere and stratosphere. The calculations did however lead to the localization of a conical intersection point through which a specific loss of H2 could take place. However, the conical intersection lies at 5.4 eV relative to the ground state molecule at equilibrium and is thus inaccessible via single photon excitation at tropospheric and stratospheric wavelengths. In addition to the ab initio investigation we have carried out a femtosecond pump-probe experiment using a 266/400 nm excitation. The results show that the timescale for the internal conversion from the initially prepared high-lying Rydberg states is on the order of a picosecond. This process populates the n --> pi* first excited singlet state which then survives for a substantially longer time before it is depopulated to form hot ground state or triplet-excited molecules that can then decompose.

We present high-level computational predictions regarding a novel uncatalysed, yet feasible, C-C bond forming reaction.

A set of design rules for the prediction of relative stabilities of methoxy substituted naphthyl methyl carbocations are presented based on a series of DFT calculations. The peri-effect, over-crowding, substitutions on the ring carrying the CH(2)(+) group and substitution on the opposite ring are the principal factors that influence the stability of the carbocations. All of these factors have to be taken simultaneously into account. The most pronounced destabilization occurs when the methyl part of the methoxy substituent lies out of the plane of the aromatic core because this causes the resonance stabilization of the carbocation to become hindered. The performance of the DFT-calculations was assessed on the results of a G3(MP2)//B3LYP calculation-a method that is known to predict energies to within chemical accuracy. These values were found to compare well with those obtained at the B3LYP/6-31G(d) level. Thus, a computationally inexpensive method such as the B3LYP/6-31G(d) might prove to be a powerful tool in the design of future complex extended aromatic systems.