Many-body perturbation theory electronic structure calculations for the methoxy radical. I. Determination of Jahn–Teller energy surfaces, spin–orbit splitting, and Zeeman effect

Abstract

Many-body perturbation theory calculations of the electronic structure are reported for C3v and Jahn–Teller distorted conformations of the methoxy radical CH3O. The Jahn–Teller distortion reduces the energy relative to the minimum energy for the C3v structure by −0.64 kcal/mol. Furthermore, the dynamic Jahn–Teller effect reduces the calculated spin–orbit splitting from 78 to 37 cm−1. An analysis of the Jahn–Teller energy surface yields the e mode vibrational frequencies (ν4 = 2314, ν5 = 1066, ν6 = 792 cm−1) and Coriolis coupling coefficients (ζ4 = 0.065, ζ5 = −0.152, and ζ6 = 0.186) for the ground state. The orbital g factor g0 = 0.647 was calculated and used to determine the components of the g tensor for free methoxy and matrix-trapped methoxy. For free methoxy, g∥ = 2.645 and g⊥ = 0; for the matrix-trapped radical, experimental data was used to calculate the splitting 1.7 kcal/mol of the methoxy energy level caused by its site environment. This splitting quenches g∥ to a value of 2.096.