Laser-induced fluorescence and dispersed-fluorescence spectroscopy of the à 2 e - X 2 A 1 transition of jet-cooled calcium methoxide (CaOCH3) radicals

Abstract

Laser-induced fluorescence (LIF) and dispersed fluorescence (DF) spectra of the Ã2E-X2A1 electronic transition of the calcium methoxide (CaOCH3) radical have been obtained under jet-cooled conditions. Complete active space self-consistent field and coupled-cluster calculations on the free radical were performed to aid the assignment of vibronic transitions observed in the LIF/DF spectra. In addition to dominant spectral features that are well reproduced by vibrational frequencies and Franck-Condon (FC) factors calculated ab initio, the FC matrix for the Ã2E-X2A1 electronic transition contains considerable off-diagonal elements that connect (i) the CaO-stretch (ν4) mode and non-CaO stretch modes and (ii) the asymmetric CaOC stretch (ν3) and the CaOC bending (ν8) modes. The Jahn-Teller and pseudo-Jahn-Teller interactions involving the Ã2E state as well as the spin-orbit interaction induce additional vibronic transitions that are not allowed under the Born-Oppenheimer approximation. Additionally, anharmonic vibrational terms in the ground state induce transitions that are forbidden in the harmonic-oscillator approximation. Spin-orbit splitting has been observed for several vibrational levels of the Ã2E state, and an essentially constant value was measured at all levels accessed in the LIF experiment. Implications of the present spectroscopic investigation to the proposed schemes of laser-cooling MOCH3 (M = alkaline earth metals) molecules and detection of time-reversal-symmetry-violating interactions are discussed.