EPR spectra of deuterated methyl radicals trapped in low temperature matrices

EPR spectra of CHD2 and CD3 radicals are investigated in low-temperature matrices of H-2, D-2, and Ne at temperatures of 1.6-4.2 K. A method of condensation from the gas phase on a cold substrate is used. With decreasing sample temperature. a transformation of the shape of the CD3 spectrum in H-2, D-2, and Ne matrices and CHD2 spectrum in H-2 and Ne is 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. The temperature behavior of the EPR spectra for radicals trapped in various matrices are compared on the basis of the present data and known results for deuterated methyl radicals in Ar obtained in photolytic experiments. As a result the existence of a hindering barrier for the radical rotation is suggested. (C) 2005 American Institute of Physics.