Isotopic study of the B∼2A1-X∼2A1 transition of calcium monomethoxide using laser excitation and population depletion spectroscopy

High resolution excitation spectra have been obtained of the 0-0 band of the B∼2A1-X∼2A1 transition of four isotopologues, CaO12CH3, CaO13CH3, CaO12CD3 and CaO13CD3 of calcium monomethoxide. The deuterated species were found to have unexpectedly complicated spectra, and definitive rotational assignments were possible only from investigation by optical optical double resonance (OODR) population depletion spectroscopy. This confirmed the assignment of the CaO12CD3 spectrum, and proved crucial in assigning the K-structure and spin components for CaO13CD3. The B∼2A1 state was found to be well described by the symmetric rotor model with C3v symmetry for both hydride species but, for the deuterides, the K-structure and spin rotation splittings were irregular, especially for CaO13CD3 where the K = 0 and 1 levels were heavily perturbed. The changes in the A constant determined for the hydride suggest that the CH3 umbrella opens by ∼0.4°, i.e., 0.2° further on excitation to the B∼2A1 state than on excitation to the lower-lying A∼2E state (geometry change established in an earlier experiment by Crozet et al. [P. Crozet, A.J. Ross, C. Linton, A.G. Adam, W.S. Hopkins, R.J. Le Roy, J. Mol. Spectrosc. 229 (2005), 224-230]).