IR-Induced Photoisomerization of Glycolic Acid Isolated in Low-Temperature Inert Matrices

Abstract

Glycolic acid (HO−CH2−COOH) monomers isolated in low-temperature argon and krypton matrices were studied using FTIR spectroscopy. The most stable SSC conformer of the compound dominated in the matrices immediately after their deposition. Upon broadband infrared irradiation, two minor conformers (GAC and AAT) were photogenerated. No other forms of glycolic acid were populated, either thermally or photochemically. Systematic monitoring of the progress of the IR-induced phototransformations (over a time scale of 20−140 min) allowed one to distinguish between the primary (GAC) and secondary (AAT) photoproducts. The assignment of experimental spectra to the different conformers was based on the results of IR irradiation of the samples and was assisted by the theoretical calculations carried out at the MP2/aug-cc-pVDZ level. Theoretical pathways for intramolecular rotation in the glycolic acid monomer were investigated at the MP2/6-31++G(d,p) level. Lack of conformers other than SSC, GAC, and AAT in the IR-irradiated matrices was explained in terms of energy barriers separating different forms of the compound.