Spin–orbit autoionization and intensities in the double-resonant delayed pulsed-field threshold photoionization of HCl

State-selected delayed pulsed-field threshold photoionization spectra of HCl and DCl are recorded in double-resonant transitions through the F 1Δ, E 1Σ+, and g 3Σ− states of the 4pπ Rydberg configuration. Comparison of observed rotational line strengths with calculated spectra, as well as with available time-of-flight photoelectron spectra, provides useful insight on the influence of spin–orbit and rotational autoionization on delayed pulsed-field threshold photoionization of HCl. Spin–orbit and rotational autoionization are seen to dramatically reduce the ion rotational intensity associated with the upper spin–orbit level of the ion.