EPR spectra of deuterated methyl radicals trapped in low temperature matrices

Abstract

EPR spectra of CHD₂, and CD₃ radicals have been investigated in low-temperature matrices of H₂, D₂, and Ne at temperatures 1.6–4.2 K. A method of condensation from the gas phase on a cold substrate has been used. With decreasing sample temperature, a transformation of the shape of the CD₃ spectrum in H₂, D₂, and Ne matrices and CHD₂ spectrum in H₂ and Ne was observed. This transformation was reversible in the above temperature range. The temperature effects are explained as reflecting a change in the populations of the lowest rotational states of the radicals. Based on the present data and known results for deuterated methyl radicals in Ar obtained in photolytic experiments, we compare the temperature behavior of the EPR spectra for the radicals trapped in various matrices. As a result an existence of a hindering barrier for the radical rotation is suggested.