Low-temperature tunneling of CH3 quantum rotor in van der Waals solids

Abstract

Motional quantum effects of tunneling methyl radical isolated in solid gases as they appear on experimental electron paramagnetic resonance (EPR) spectra are examined. Obtained analytical expressions of the tunneling frequency for methyl rotor/torsional-oscillator utilizing localized Hermite polynomials are compared to full numerical computations and tested against experimental EPR lineshape simulations. In particular, the X-band of methyl radical was displaying partial anisotropy averaging even at lowest temperatures. EPR lineshape simulations involving rotational dynamics were applied for the accurate determination of the potential barrier and the tunneling frequency. Tunneling frequency, as the splitting between the A and E torsional levels by the presence of a periodic C 3 model potential with periodic boundary conditions, was computed and related to the EPRlineshape alteration. The corresponding C 2 rotary tunneling about the in-plane axes of methyl was also studied while both the C 2 and C 3 rotations were compared with the rotation of deuteriated methyl radical.