Near-infrared laser induced conformational change and UV laser photolysis of glycine in low-temperature matrices: Observation of a short-lived conformer

The near-infrared spectrum (NIR) of glycine was measured in Ar and Kr matrices. Matrix-isolated glycine was irradiated with NIR laser light at the first OH or NH stretching overtone bands of the three main glycine (ttt/Ip, ccc/IIn, tct/IIIp) conformers. The main conversion paths and their efficiencies are described qualitatively, and it is shown that there are significant differences in the conversion paths in Ar and Kr. In the detailed analysis of these experiments many new, formerly unobserved low-intensity transitions of the three main conformers were identified, and in addition a short-lived (tunneling half-life is 5 ± 2 s) higher energy conformer (ttc/VIp) was observed during the irradiation at the first OH stretching overtone of ttt/Ip. The UV spectrum of glycine was also measured in Ar matrix, and the first two absorption bands of conformers ttt/Ip and ccc/IIn were identified. UV laser irradiation at longer (240 nm) wavelengths promotes rotamerization, while at shorter wavelengths (235 and 213.5 nm) it results in depletion of the different conformers with different rates. Analysis of spectra recorded after UV irradiation showed that the two main photodecomposition processes are decarboxylation and H2O loss, forming methylamine and NH2CHCO, respectively.

► Near-IR, Mid-IR and UV spectra of glycine in solid Ar and Kr were recorded.
► NIR laser induced conformational changes of matrix-isolated glycine were investigated.
► The main conversion paths and their efficiencies are described qualitatively.
► A formerly unobserved short-lived higher energy conformer (t1/2 = 5 s) was identified.
► UV induced conformational changes and UV photodecomposition products were analyzed.