Spin–orbit and rotational autoionization in HCl and DCl

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Abstract
The rotationally resolved spin–orbit autoionization spectrum of HCl has been obtained in double resonance via levels of lowest angular momentum in v=0 of the 4pσ D 1Π state. A self‐consistent assignment is offered for the portion of the spectrum ranging over principal quantum numbers from 13 to 18. Positions established in HCl point to series of similar quantum defect converging to the rotational ground state of DCl+ 2Π1/2. HCl features are further confirmed by comparison with earlier double‐resonance spectra obtained via the F 1Δ state, and with vuv autoionization spectra observed in single‐photon transitions from the neutral ground state. Multichannel quantum defect theory calculations have been carried out, which introduce 28 parameters corresponding to the quantum defects, transition moments, and s–d l‐mixing coefficients for Rydberg states of HCl in Hund’s case (a). As output they predict positions and intensities for transitions involving all 53 channels accessible in Hund’s case (e) for l ranging from 0 to 2 and J from 1 to 2. The same parameters for both isotopes yield reasonable correspondence between experiment and theory for all the major resonances in HCl and DCl from principal quantum number 13 to 18 (about 70 resonances), with an average ΔE less than 3 cm−1.