A concerted hydrogen atom transfer mechanism has been elucidated for the isomerization of trans-HCOH to H2CO using a variety of ab initio and density functional theory methods. This work places specific emphasis on the role water molecules can play as a catalyst for this reaction and the mechanism by which this is achieved. This is of particular importance in the context of molecular ices in the interstellar medium because the presence of water in this reaction reduces the activation energy by at least 80%, which is accompanied by a significant enhancement of the reaction rate, at ≤300 K.
Iodine, when released into the environment, contributes to the oxidizing capacity of the atmosphere through the catalytic destruction of ozone [1, 2]. Iodine-131 can be released during a severe nuclear accident and can be carcinogenic for humans [3]. In the literature, there are missing pieces of knowledge about interactions between iodinated compounds and aerosols. In this context, this work consists in investigating the adsorption on sea salt aerosols of gaseous methyl iodide (CH3I), diiodomethane (CH2I2), and water. We have used two different methods: a periodic approach using Quantum ESPRESSO [4, 5] and a cluster QM/QM' approach using the ONIOM method [6] from Gaussian 16 [7]. We have computed the adsorption energies and the shift in vibrational frequencies, due to adsorption. We have shown that the vibrational frequency shifts are small, mainly because there is no strong coupling between the adsorbates and the NaCl (001) surface, as illustrated by the low values of the adsorption energies.
(1) Saiz-Lopez, A.; Plane, J. M. C.; Baker, A. R.; Carpenter, L. J.; von Glasow, R.; Gomez Martin, J. C.; McFiggans, G.; Saunders, R. W. Chem. Rev. 2012, 112, 1773-1804
(2) Calvert, J. G.; Lindberg, S. E. Atmospheric Environ. 2004, 38, 5087-5104
(3) Dobyns, B. M.; Sheline, G. E.; Workman, J. B.; Tompkins, E. A.; McConahey, W. M.; Becker, D. V. J. Clin. Endocrinol. Metab. 1974, 38, 976
(4) Giannozzi, P. et al. J. Phys. Condens. Matter 2009, 21, 395502
(5) Giannozzi, P. et al. J. Phys. Condens. Matter 2017, 29, 465901
(6) Svensson, M.; Humbel, S.; Froese, R. D.; Matsubara, T.; Sieber, S.; Morokuma, K. J. Phys. Chem. 1996, 100, 19357-19363
(7) Frisch, M. J. et al. Gaussian 16 Revision B.01, Gaussian Inc. Wallingford CT, 2016
1. Absolute photoionization cross section of the C60 radical cation in the 8 to 25 eV photon energy range measured using the ion trap method. 2. Absolute photoionization cross section of the C60 radical cation in the 25 to 45 eV photon energy range measured using the merged-beam technique. 3. Theoretical absolute photoabsorption cross section of the C60 radical cation from PBE real time TDDFT from the octopus code (version 4.1.2, LibXC revision : 11533 [vxc_inc.F90 2013-11-18]. 4. Theoretical absolute photoabsorption cross section of the C60 molecule from PBE real time TDDFT from the octopus code (version 4.1.2, LibXC revision : 11533 [vxc_inc.F90 2013-11-18]). These data were published here: Data published here: 10.1021/acs.jpclett.6b02558
Abstract We present novel results of the analysis of the electronic structure of two aliphatic esters: methyl butyrate and methyl valerate. High-resolution photoabsorption spectra were collected and analyzed over the energy range 4.0–10.8 eV and showed for both the molecules not only a clear band of the HOMO to LUMO transition, but also vibronic structure associated with the first Rydberg-valence transition. Photoelectron spectra recorded from 9 to over 28 eV revealed many ionization states with the first adiabatic ionization energies found to be 9.977 eV and 9.959 eV for methyl butyrate and methyl valerate, respectively. Ab initio calculations have been performed in order to help assign the photoabsorption and photoelectron features. Photolysis life times in the atmosphere were calculated revealing that photolysis is not competitive over hydroxyl radical scavenging in the process of removal of these esters from the atmosphere. Graphical abstract
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