Addition to and revision of the HI Rydberg states energy region

Abstract

Mass resolved REMPI data was recorded for jet cooled HI(g) for two-photon excitation in the region of 74 200 – 80 300 cm−1. REMPI spectra of the ions (HI+, I+ and H+) were derived from the data. The spectra revealed dense and overlapping rotational peak structure due to two-photon resonant transitions to number of Rydberg and ion-pair molecular vibrational states as well as iodine atom (2 + 1) REMPI peaks. A total of 16 Rydberg state spectra and 9 ion-pair state spectra were identified and simulated to derive spectroscopic constants (band origin (ν0) and 1st and 2nd order rotational constants (B′, D′)) for the excited states. Further analysis of the results for the Rydberg states and inspection of the spectral structure allowed more thorough characterization of the states as well as reassignment of some previously reported spectra. Detailed quantum defect analyses were particularly useful in that respect. The states could be specified by term symbols, ion core symmetries, Rydberg electron principal quantum numbers and configurations as well as vibrational quantum numbers. An attempt was made to assign the ion-pair spectra to vibrational quantum numbers. Relevant results on Rydberg and ion-pair states of HI, from the literature are summarized in the paper.