Near-infrared absorption spectrum of the Ar-HD complex: A theoretical study of predissociation effects

Results of close-coupling calculations on the near-infrared absorption by t he Ar-HD(v=0,j=1) complex, exploiting the best available empirical and theo retical models of intermolecular potential and of induced-dipole moment for Ar-H-2, are reported. The first quantitative description of the S-1(1) ban d of the spectrum is given, including transition energies, linewidths, and intensities, and the description of the Q(1)(1) band, included in the recen t study on Ar-HD [J. Chem. Phys. 109, 10823 (1998)], is completed with calc ulation of the spectrum shape. A pattern of pairs of lines of distinct widt hs and heights is found in the T- and N-transition regions of the S-1(1) ba nd. The narrow lines in the pairs (widths similar to0.1-0.2 cm(-1)) result from transitions between bound and predissociating states. The wider lines (about 6-10 times) appear due to transitions between predissociating states . The relations between heights of lines in the pairs differ qualitatively from the relative intensities of the corresponding lines in the S-1(1) band of the absorption spectrum of Ar-H-2. In the Q(1)(1) band, transitions bet ween states predissociating rotationally are found to be the only ones whic h have discernible impact on the line contour. Results of this work and the recent results on the Ar-HD(v=0,j=0) complex are summarized in a discussio n of effects of the asymmetric isotopic substitution on the absorption spec trum shape. (C) 2001 American Institute of Physics.