An EPR study on the radiolysis of isolated ethanol molecules in solid argon and xenon: matrix control of radiation-induced generation of radicals in cryogenic media

Abstract

This paper addresses the basic question of the impact of a chemically inert environment on the radiation-induced transformations of isolated organic molecules in icy media at cryogenic temperatures with possible...

Radiation-induced transformations of matrix-isolated ethanol molecules at cryogenic temperatures: an FTIR study

“…Finally, the yield of the formyl and methyl radicals in Ar seems to significantly exceed those in Ne, Kr, and Xe, also in line with the EPR data. 31 The observations outlined above are generally confirmed by the results of the experiments with isotopically substituted ethanol (C 2 D 5 OH; see Fig. 2).…”

“…S1 of ESI †). Based on the previously reported spectroscopic data, 26,31, 64 In addition to known molecular species, we observed previously unreported absorption features (Fig. 2) in the FTIR spectra of the irradiated C 2 H 5 OH/Ng matrices with maxima at 1249.1, 1247.0, 1246.2, and 1245.1 cm À1 in Ne, Ar, Kr, and Xe, respectively.…”

“…Meanwhile, according to the quantum-chemical calculations at the CCSD/cc-pVTZ level of theory, 65 the most intense absorption band of CH 3 CHOH (CCO bend ) has a harmonic frequency of 1307 cm À1 , which is in reasonable agreement with the experimental data, taking into account the anharmonicity and medium effects (the isotopic substitution shift also looks reasonable for this vibrational mode). It should be noted that our previous EPR data 31 clearly demonstrates that the CH 3 CHOH radical is the key paramagnetic species formed as a result of the radiation-induced transformations of isolated ethanol molecules in a xenon matrix but not in argon. In line with this finding, the relative intensity of the absorption band attributed to the CH 3 CHOH radical increases in the order Ne o Ar o Kr o Xe.…”

“…68 Meanwhile, no proof for the stabilization of the ethoxy radical after the radiolysis of ethanol in noble gas matrices was found in our EPR studies. 31 Furthermore, the IR absorptions of its analogue (methoxy radical, CH 3 O , known in a para-hydrogen matrix 69 ) were not detected in the FTIR studies of irradiated CH 3 OH/Ng systems. 26 For this reason, it was suggested 31 that rearrangement (3) occurs efficiently in xenon (and, possibly, in other noble gas matrices) even at very low temperatures (5-7 K).…”

“…Recently, we have comparatively examined the formation of radicals resulting from the X-ray irradiation of ethanol isolated in solid argon and xenon using the EPR technique. 31 It was found that changing the matrix environment results in a drastic change in the principal mode of bond rupture (from predominating C-C bond cleavage in argon to C-H bond cleavage in xenon). Meanwhile, it is clear that the formation of radicals detected by EPR represents only a part of complex radiation-induced transformations of ethanol molecules in cryogenic environments.…”