VUV Photofragmentation of Chloroiodomethane: The Iso-CH₂I–Cl and Iso-CH₂Cl–I Radical Cation Formation

Abstract

Dihalomethanes XCH 2 Y (X and Y = F, Cl, Br, and I) are a class of compounds involved in several processes leading to the release of halogen atoms, ozone consumption, and aerosol particle formation. Neutral dihalomethanes have been largely studied, but chemical physics properties and processes involving their radical ions, like the pathways of their decomposition, have not been completely investigated. In this work the photodissociation dynamics of the ClCH 2 I molecule has been explored in the photon energy range 9–21 eV using both VUV rare gas discharge lamps and synchrotron radiation. The experiments show that, among the different fragment ions, CH 2 I + and CH 2 Cl + , which correspond to the Cl- and I-losses, respectively, play a dominant role. The experimental ionization energy of ClCH 2 I and the appearance energies of the CH 2 I + and CH 2 Cl + ions are in agreement with the theoretical results obtained at the MP2/CCSD(T) level of theory. Computational investigations have been also performed to study the isomerization of geminal [ClCH 2 I] •+ into the iso-chloroiodomethane isomers: [CH 2 I–Cl] •+ and [CH 2 Cl–I] •+ .

Charge-Separated Reactive Intermediates from the UV Photodissociation of Chlorobenzene in Solution

“…As an alternative to an ion pair comprising two separated ions, the intermediate absorption may instead come from a charge-transfer band of a complex with ion-pair character, denoted here as Ph + -Cl – . Similar complexes with ion-pair character can be formed by photoexcitation of halogenated alkanes and have been identified as reactive intermediates in both experimental and theoretical studies. − The corresponding complexes of CCl 4 and CHCl 3 , which are referred to in the photochemistry and pulsed radiolysis literature as iso- CCl 4 and iso- CHCl 3 to indicate their isomeric structures, exhibit strong ion pair character. For example, computational evidence shows that iso -CCl 4 can be regarded as a Cl – -ClCCl 2 + species .…”

Ionic Route to Atmospheric Relevant HO2 and Protonated Formaldehyde from Methanol Cation and O2

“…The experiments were performed at the Circular Polarization (CiPo) beamline of ELETTRA synchrotron, with the experimental set-up and procedures described in our previous works [36][37][38]. Briefly, the radiation was supplied by an electromagnetic elliptical undulator/wiggler and monochromatized by a Normal Incidence Monochromator (NIM) in the vacuum ultraviolet (VUV) energy range 8-40 eV.…”

Ion Chemistry of Carbon Dioxide in Nonthermal Reaction with Molecular Hydrogen

“…Although there are several setups for the plasma-based CO 2 conversion, the mechanistic insights into CO 2 transformation are not well understood, and this prevents the prediction of a realistic trend on product yields and selectivity. Hence, an accurate experimental and theoretical analysis at the molecular level of the reactions of the “internally excited” CO 2 · + with these neutrals is undoubtedly relevant. − The reaction of carbon dioxide cation with molecular hydrogen has been already studied at low temperatures (15–300 K) under thermal conditions by Gerlich and co-workers . Instead, in the present study, we report an experimental and theoretical study of the same reaction with different internal energy of the carbon dioxide cation: the tunable synchrotron radiation has been used to excite vibrationally the reagent ions and the experimental results has been analyzed by developing a theoretical model based on the variational transition state theory (VTST) .…”