2 research outputs found
Mechanisms of Radiation-Induced Degradation of CFCl<sub>3</sub> and CF<sub>2</sub>Cl<sub>2</sub> in Noble-Gas Matrixes: An Evidence for “Hot” Ionic Channels in the Solid Phase
The
X-ray-induced transformations of simple chlorofluorocarbons
(CFCl<sub>3</sub> and CF<sub>2</sub>Cl<sub>2</sub>) in solid noble-gas
matrixes (Ne, Ar, Kr, and Xe) at 7 K were studied in order to elucidate
basic mechanisms of the radiation–chemical degradation with
possible implications for stratospheric and extraterrestrial ice chemistry.
The decomposition of parent molecules and formation of products were
monitored by FTIR spectroscopy, and the identification was supported
by <i>ab initio</i> calculations at the CCSDÂ(T) level. It
was shown that the ionic reaction channels were predominating in most
cases (except for CF<sub>2</sub>Cl<sub>2</sub>/Xe system). The primary
radical cations (CFCl<sub>3</sub><sup>+•</sup> and CF<sub>2</sub>Cl<sub>2</sub><sup>+•</sup>) are either stabilized in matrixes
or undergo fragmentation to yield the corresponding secondary cations
(CFCl<sub>2</sub><sup>+</sup>, CCl<sub>3</sub><sup>+</sup>, CF<sub>2</sub>Cl<sup>+</sup>) and halogen atoms. The probability of fragmentation
through different channels demonstrates a remarkable matrix dependence,
which was explained by the effect of excess energy resulting from
the exothermic positive hole transfer from matrix atoms to freon molecules.
A qualitative correlation between “hot” ionic fragmentation
at low temperatures and gas-phase ion energetics was found. However,
dissociative electron attachment leads to formation of neutral radicals
(CFCl<sub>2</sub><sup>•</sup> or CF<sub>2</sub>Cl<sup>•</sup>) and chloride anions. One more possible way of dissociative electron
attachment in the case of CF<sub>2</sub>Cl<sub>2</sub> is formation
of CF<sub>2</sub><sup>••</sup> and Cl<sub>2</sub><sup>–•</sup>. A general scheme of the radiation-induced
processes is proposed