Infrared-induced conformational isomerization of ethylene glycol in a low-temperature argon matrix

Abstract

The infrared spectra of ethylene glycol and its three deuterated species trapped in low-temperature Ar matrices show irreversible changes upon exposure to the radiation from the light source of an infrared spectrophotometer. Spectral changes in the O-H stretching region demonstrate the existence of two intramolecularly hydrogen-bonded conformers, namely, TGG′ and GGG′, which are predominant immediately after deposition but diminish under irradiation through isomerization to other conformers. Analysis of the spectral changes in the C-O stretching and OH bending regions suggests that the extended all-trans conformer, TTT, is the main product of isomerization. Therefore, the main pathways of conformational isomerization under study are those which go from both TGG′ and GGG′ to TTT. This conclusion is consistent with more detailed vibrational assignments based on normal-coordinate calculations. Further, the intensities of bands assigned to TGG′ are found to decrease faster than those of bands assigned to GGG′. Experiments with filter show that the infrared light between 3950 and 3600 cm−1, especially in the 3700-3600 cm−1 region, is responsible for the conformational isomerization. A possible isomerization mechanism is proposed.