EPR spectra and rotation of CH₃, CH₂D, CHD₂, and CD₃ radicals in solid H₂

Abstract

EPR spectra of CH₃, CH₂D, CHD₂, and CD₃ radicals have been observed in H₂ matrix in the temperature range 1.6-4.2 K. The radicals were obtained by condensation on a cold substrate of two gas flows: deuterium mixed with 2 mol % methane passed through a discharge and pure hydrogen avoiding the discharge. The CD₃ and CHD₂ spectra were found to be a superposition of two spectra: high-temperature and low-temperature. A transformation of the shape of CD₃ and CHD₂ spectrum with decreasing sample temperature was observed. This is attributed to a change in the populations of the lowest rotational states of the radicals. Compared to known results for deuterated methyl radicals in Ar, the present observations suggest an existence of a hindering barrier for the radical rotation in solid H₂.