Fermi resonance and conformation in glycolaldehyde particles

Abstract

The infrared spectra of gas-phase glycolaldehyde and small glycolaldehyde particles both exhibit a split carbonyl band around 1730 cm1. Ab initio calculations show that this splitting can be traced back to a Fermi resonance involving the C=O-stretching band and the first overtone of the CC-stretching band. The analysis of this resonance leads to detailed information about the conformation of glycolaldehyde in the particles. The results can be summarized as follows. (i) In the particles, monomers with OCCO dihedral angles of 0° and CCOH dihedral angles around 50° are strongly preferred. (ii) The intramolecular hydrogen bond observed in the gas phase is partly replaced by intermolecular hydrogen bonds. (iii) The calculated infrared spectrum and the results from the Fermi resonance analysis are in good agreement with the formation of long chains of monomeric glycolaldehyde. This is in contrast to the solid bulk, which consists of chemically bound dimers. Key words: Fermi resonance, conformation, glycolaldehyde particles, hydroxyacetone particles, Fourier transform infrared spectroscopy.