FTIR study of the second stretching vibrational overtone system of H₃⁷⁰GeD: example of an almost asymmetric rotor band

Abstract

The FTIR spectrum of monoisotopic H₃ ⁷⁰GeD around 6100 cm^-1 was recorded with a resolution of about 0·012 cm^-1. A perpendicular-type band, v ₀(E) = 6129·441 cm^-1, is observed, which is unperturbed for K′ ⩽ 1>2. Its rotational analysis reveals, in addition to rovibrational r and q resonance effects within the E vibrational state, a strong rovibrational α resonance perturbation by an almost degenerate perturber of A₁ symmetry, v ₀ = 6129·434 cm^-1. Owing to intensity perturbations the parallel component is very weak in spite of a transition moment ratio M(E)/M(A₁) of about -2. The rovibrational energy level pattern is indicative of local mode behaviour of the v _(GeH) = 3 state, in which Coriolis effects are almost absent and simple arithmetic relations between vibration-rotation parameters fulfilled as expected. This gives rise to an excited state energy level pattern almost consistent with that of an asymmetric rotor.