Quantum Effects in Deuterium Labelled Radicals at Low Temperature

Abstract

Recent progress in deuterium labelling studies of radicals in the solid state is reviewed. Emphasis is placed on quantum effects at low temperature. The high-resolution ESR spectra of partially 2D labelled methyl radicals were radiolytically generated together with a hydrogen atom — methyl radical pair in an Ar matrix at cryogenic temperatures. The methyl radical spectra are discussed in terms of nuclear spin-rotation couplings using a three-dimensional free quantum-rotor model. A hydrogen atom — hydrogen molecule (H...H2) pair formation in Ar is discussed in terms of 2D isotope effects on quantum mechanical tunnelling reaction. The H2 molecule as a “quantum solid” for high-resolution ESR spectroscopy is presented. 2D effects on zero point vibrational energy (ZPVE) were presented in combination with Jahn-Teller distortion of methane and tetramethylsilane radical cations with a high symmetry of T d structure originally as well as chemically important cyclohexane radical cations. Furthermore, 2D isotope effects on methyl group conformation were exemplified using selectively deuterated dimethylether and monofluoromethane radical cations; the experimental results were also interpreted in terms of ZPVE incorporated with the mass difference of the two hydrogen isotopes.