ROTATIONAL STRUCTURE NEAR THE LOCAL MODE LIMIT - THE 2-NU-1-BAND AND NU-1+NU-4-BAND OF (H3GEI)-GE-70 AND (H3GEBR)-GE-74-BR-79

The overtones of the GeH stretching vibration near 4150 cm-1 of the monoisotopic germyl halides H3 74Ge79Br and H3 70GeI have been studied with an effective resolution (FWHM) of 7 × 10-3 cm-1. The rovibrational analysis in the normal mode approach reveals strong local perturbations for the bromide which limit the SD of the fit of 1687 somewhat arbitrarily selected lines to 2.3 × 10-3 cm-1. On the other hand, 3734 transitions of H3 70GeI were fitted with a SD of 0.39 × 10-3 cm-1, which is almost the precision of the data, to a model involving a perpendicular component, ν0 = 4163.7324 cm-1, interacting by a weak Coriolis resonance with a parallel component, ν0 = 4161.7859 cm-1. Comparison of the vibrational and rotational parameters of the v(GeH) = 2 states, for both species, with those associated with the vibrational fundamentals, discloses that these v1 = 2 and v1 = v4 = 1 states behave almost as expected for the components of the (200) manifold in the local mode picture. Energy levels belonging to the (110) manifold have also been discerned in the iodide through a Coriolis-type interaction. Rovibrational parameters obtained from the overtone analysis, which is unprecedented for a symmetric top with three coupled M-H oscillators, are compared with predictions for the local mode limit. © 1991.