Spin–orbit and electronic autoionization in HCl

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Abstract
The high resolution relative photoionization cross section for HCl is reported in the wavelength region 720–975 Å. In addition, results of calculations are presented for spin–orbit autoionization in the energy region between the X 2Π3/2 and X 2Π1/2 ionization thresholds and for electrostatic autoionization in the energy region containing Rydberg series converging to the A 2Σ+ excited ionic state. For the case of spin–orbit autoionization in the region just above the X 2Π3/2 ionic threshold, it is found that the energy positions of the first peaks are approximately correct if the ionization potential is modified by ≊80 cm−1; however the intensities of the peaks are strongly perturbed, most probably by high lying vibrational levels of the V 1Σ+ valence state. In the wavelength region 780–930 Å, two progressions of Rydberg states converging to the A 2Σ+ excited ionic state and autoionized by electrostatic interaction are also studied by ab initio multichannel quantum defect theory. Qualitative agreement with the experimental data is obtained by a slight adjustment of some quantum defects, the other parameters being those obtained by ab initio calculations. Comparison with the absorption spectra of both HCl and DCl is also made. Progression I of Terwilliger and Smith [J. Chem. Phys. 63, 1008 (1975)] is reassigned to the (A 2Σ+) 3dπ 1Π state and progression II to the (A2Σ+) 3pπ 1Π state on which is superimposed the (A 2Σ+) 3dσ 1Σ+ state. The large difference between the quantum defects of dπ and dσ states precludes the existence of a 3d complex.