PHOTOSELECTION AND THE STRUCTURE OF HIGHLY EXCITED-STATES - ROTATIONALLY RESOLVED SPIN ORBIT AUTOIONIZATION SPECTRUM OF HCL

Ultraviolet two-photon photoselection, followed by visible one-photon absorption is applied to HCl to record the first double-resonant spin-orbit autoionization spectrum of a hydrogen halide, and the first rotationally resolved such spectrum of HCl. The J = 2 level of the F1-DELTA-2 (v = 0) Rydberg state serves as the intermediate two-photon resonance. The ionization-detected absorption spectrum from this initial state, scanned across the 634 cm-1 interval between the lower 2-PI-3/2 and upper 2-PI-1/2 thresholds, shows a complex system consisting of hundreds of sharp lines converging to the accessible rotational limits of the upper spin-orbit threshold. The complexity of the spectrum is attributed to the relaxed selection rules associated with dipole transitions from a state in Hund's case (a) to a manifold approaching Hund's case (e), in concert with the irregularities expected for angular momemtum coupling intermediate between the limits of case (c) and case (e). A simple case (e) fit over the central portion of the spectrum yields tentative assignment of a number of series converging to the J + = 1/2, 3/2, and 5/2 levels of the ion. No evidence is found for series converging to higher rotational levels of the ion, even though such series are not excluded by angular momentum selection rules; transitions to Rydberg electronic angular momenta required for access to states of higher J + are found associated with series observed converging to lower rotational thresholds.