MATRIX-ISOLATION INFRARED AND THEORETICAL-STUDIES OF THE GLYCINE CONFORMERS

The LR spectra of nonionized glycine and its deuterated derivatives is olated in the low-temperature argon matrices have been measured, and f or the first time the infrared spectral characteristics of the three m ost stable conformers have been determined and assigned. Correlated le vel ab initio and density functional theory (DFT) calculations of IR f requencies and intensities with extended basis sets were performed and their results were employed to separate the bands of the glycine conf ormers in the experimental spectra and to assist the assignment. The i ntramolecular interconversion, conformer III double right arrow confor mer I, which is observed in the matrices at temperatures higher than 1 3 K, was found to cause a significant decrease of the band intensities of conformer III in the spectra. This phenomenon was used to distingu ish the vibrational bands of this conformer from the bands of the othe r conformers. The reliability of the Moller-Plesset second-order pertu rbation theory (MP2) method and the DFT method with the three-paramete r density functional, Becke3LYP, in the prediction of the IR spectra o f the nonionized glycine conformers was examined. We found that the DF T/Becke3LYP method with aug-cc pVDZ basis set yields vibrational frequ encies of the glycine conformers very similar to the MP2 results. Both DFT and MP2 results are in the excellent agreement with the experimen tal data.