Jahn-Teller effect in CH2DO∕CHD2O(X̃(2)E): vibronic coupling of all vibrational modes.

For the Jahn-Teller active methoxy radical CH3O∕CD3O(X̃(2)E), only the degenerate vibrational modes break the C3v geometric symmetry. For the isotopologues CH2DO∕CHD2O, all their normal vibrational motions break the C3v geometric symmetry, which results in a splitting of the adiabatic potential energy surfaces (APESs), that is, all vibrational modes are Jahn-Teller active. Therefore, each fundamental vibrational energy level of CH2DO∕CHD2O splits into two levels due to a combination of Jahn-Teller and spin-orbit interactions. In this work we report an ab initio calculation of the spin-vibronic energy levels of CH3O∕CH2DO∕CHD2O∕CD3O using a diabatic model. The APESs were calculated at the UCCSD(T)-F12a∕cc-pVQ(T)Z-F12a level. The vibronic parameters in the diabatic model Hamiltonian of CD3O were first determined using the least-squares fitting to the APESs. The vibronic parameters of the other three isotopologues were derived from those of CD3O using the Duschinsky rotation method. The calculated spin-vibronic energy splittings for the vibrational ground states of CH3O∕CH2DO∕CHD2O∕CD3O are 61.8∕73.5∕70.2∕54.5 cm(-1), respectively, in good agreement with the reported experimental results.