Matrix isolation spectroscopy and conformational analysis of epichlorohydrin in solid parahydrogen

Abstract

Fundamental vibrational modes of epichlorohydrin have been characterized in a solid parahydrogen matrix at 4.3 K using FTIR spectroscopy. All three stable conformations of epichlorohydrin, gauche-I, gauche-II and cis, were identified in the infrared spectra. The effect of chlorine isotopic substitution was also observed in the ν19 and ν20 vibrational modes, which correspond to the C-C-Cl bending and C-Cl stretching motions, respectively. The relative populations of three conformers of this molecule in parahydrogen have been experimentally determined from three well-separated fundamental modes (ν7,ν16 and ν18), and compared with Boltzmann populations derived from quantum chemical calculations at various temperatures. The analysis suggests that relative conformer population ratio of gauche-I:gauche-II:cis is ~65%:~24%:~11% in solid parahydrogen at 4 K. This population agrees well with the equilibrium Boltzmann distribution at room temperature, which indicates that the conformational population is preserved during the cooling process in which the epichlorohydrin molecules are trapped in solid parahydrogen.