Near-infrared absorption spectrum of the Ar-HD comples; A theoretical study of predissociation effects

摘要

Results of close-coupling calculations on the near-infrared absorption by the Ar-HD (v=0, j=1) complex. exploiting the best available empirical and theoretical models of intermolecular potential and of induced-dipole moment for Ar-H_2, are reported. The first quantitative description of the S_1 (1) band of the spectrum is given, including transition energies, linewidths, and intensities, and the description of the Q_1(1) band, included in the recent study on Ar-HD [J. Chem. Phys. 109, 10823 (1998)], is completed with calculation of the spectrum shape. A pattern of pairs of lines of distinct widths and heights is found in the T- and N - transition regions of the S_1(1) band. The narrow lines in the pairs (widths (approx) 0.1-0.2 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 between states predissociating rotationally are found to be the only ones which 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 discussion of effects of the asymmetric isotopic substitution on the absorption spectrum shape.