High-order resonance interactions in HDO: Analysis of the absorption spectrum in the 14980-15350 cm(-1) spectral region

The absorption spectrum of the HDO molecule recorded by intracavity laser a bsorption spectroscopy in the 14 980-15 350 cm(-1) spectral region was assi gned and modeled in the frame of the effective Hamiltonian approach. The sp ectrum (496 lines) results, mainly, from transitions to the rotational subl evels of the (014) bright state. An important number of transitions involvi ng the (142) and (0 12 0) highly excited bending states could be identified , borrowing their intensities through high-order resonance interactions wit h the (014) state. An original feature shown by the present analysis is tha t all the transitions involving unperturbed energy levels of the (014) stat e are exclusively of A type, while both A- and B-type transitions are obser ved when the upper states are perturbed by the resonance interactions. One hundred forty-five energy levels of the three interacting states were deriv ed from the spectrum and fitted to the effective rotational Hamiltonian in Pade-Borel approximants form with 29 varied parameters yielding an rms devi ation of 0.038 cm(-1). A few energy levels are affected by additional local resonances with perturbers which have been identified. Finally, 48 transit ions of the very weak 6 nu(1) band were assigned and fitted as an isolated band. (C) 2000 Academic Press.