MILLIMETER-WAVE ROTATIONAL SPECTROSCOPY OF MGOD AND CAOD (X(2)SIGMA(+))

Pure rotational spectra of CaOD and MgOD have been recorded in the ran ge 200-390 GHz using millimeter/sub-mm direct absorption spectroscopy. Transitions arising from the (000), (010), (020), and (100) modes hav e been measured for the (2) Sigma(+) ground electronic states of these free radicals. The data were analyzed successfully using a linear (2) Sigma(+) model for CaOD; for MgOD, only the (000) and (010) states co uld be fit with this Hamiltonian. Moreover, the (010) data required th e addition of a substantial p(Pi) term to account for contamination of excited (2) Pi electronic states. For both species, the alpha(2) vibr ation-rotation term was found to be negative, in contrast to MgOH and CaOH, suggesting a less anharmonic contribution to the bending potenti al in CaOD and MgOD. These measurements also indicate a shorter O-H bo nd in MgOH than the other alkaline earth hydroxide radicals, which lik ely results because this species is quasilinear. (C) 1995 American Ins titute of Physics.