Theoretical and neon matrix electron spin resonance studies of the methanol cation: CH3OH+, CH3OD+, CH2DOH+, and 13CH3OH+

Abstract

Four isotopes of the methanol cation radical (CH3OH+) have been generated by three independent methods and isolated in neon matrices at 4 K for a detailed electron spin resonance (ESR) investigation. The ion generation methods employed were X irradiation, photoionization, and electron ionization. The nuclear hyperfine (A tensors) measurements were compared with those obtained from ab initio extended basis set multireference configuration interaction (CI) wave functions. The relationships between geometry and electronic structures were fully explored. The trend in the large isotropic methyl hydrogen A values for the isoelectronic series CH3F+, CH3OH+, and CH3NH2+ was found to follow the trend in dissociation energies for these radical cations. The neon magnetic parameters for CH3OH+ are gx=2.0036(4) and gz=2.010(1); Aiso (methyl hydrogens)=229(1) MHz, ‖Ax‖=54(2) and ‖Az‖=80(3) MHz for the hydroxy hydrogen; ‖Ax‖=40(2) and ‖Az‖=29(4) MHz for 13C. The observed magnetic parameters for CH2DOH+ indicate an unusually large deuterium effect Aiso (CH2)=329 MHz with ‖Aiso‖=4.1(3) MHz for the methyl deuterium. These results show that averaging of the methyl hydrogen environments is occurring on the ESR time scale.