Orientation dynamics of the methyl radical and matrix molecules in solid methanes, CH$_{4}$ and CD$_{4}$, at cryogenic temperatures

Electron paramagnetic resonance (EPR) technique was used to determine temperature dependencies of the rotational level relative populations for the $A$- and $E$-state methyl radicals, CH$_{3}$, trapped in solid methane, CH$_{4}$, at 1.4 – 4.2 K and solid CO at 6 – 33 K. Peculiarities in the radical orientational motion at the cryogenic temperatures were observed. An analysis showed that, in solid CH$_{4}$ and CD$_{4}$, the molecular short-range orientation is partially preserved even in the methane orientationally disordered phase, while correlated molecular reorientation took place in the methane low temperature ordered or partially ordered phases.