Photofragmentation, state interaction, and energetics of Rydberg and ion-pair states: Resonance enhanced multiphoton ionization of HI

Abstract

Mass resolved resonance enhanced multiphoton ionization data for hydrogen iodide (HI), for two-photon resonance excitation to Rydberg and ion-pair states in the 69,600-72,400 cm(-1) region were recorded and analyzed. Spectral perturbations due to homogeneous and heterogeneous interactions between Rydberg and ion-pair states, showing as deformations in line-positions, line-intensities, and line-widths, were focused on. Parameters relevant to photodissociation processes, state interaction strengths and spectroscopic parameters for deperturbed states were derived. Overall interaction and dynamical schemes to describe the observations are proposed.

State interactions and illumination of hidden states through perturbations and observations of new states: High energy resonance enhanced multiphoton ionization of HI

“…The experimental apparatus as well as relevant equipment parameters are similar to that described in previous publications. 39,44,45 Therefore, only a brief experimental discussion will be given here.…”

“…The state interaction strength (i.e., the perturbation matrix element, W 12 , for electronic states, 1 and 2) 57 is independent of the total angular momentum quantum number, J ′ , for homogeneous interactions, but J ′ dependent for heterogeneous interactions. 56 Such interactions appear as energy level repulsion effects for levels of the interacting states with the same J ′ values, the degree of which depends on the interaction strength (W 12 ) and the energy mismatch (∆E J ′) of the interacting J ′ levels, 29,[31][32][33]45,56,58…”

“…where E 0 J ′ (1) and E 0 J ′ (2) are the zero-order energy levels for the unperturbed states 1 and 2. Furthermore, the interaction involves mixing of the states, fraction of which (c 2 (i)) also depends on W 12 and ∆E J ′ 29,31,32,45,56,58 as…”

“…5 In addition to standard absorption spectroscopic studies of the hydrogen halides, [6][7][8][9][10][11][12][13][14][15] resonance enhanced multiphoton ionization (REMPI) analyses have been widely used, allowing states, which are regularly inaccessible by single photon selection rules to be formed. Most REMPI experiments have been conducted on HCl, [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] whereas a handful of studies of HBr 26,27,[33][34][35][36][37][38][39] and HI [40][41][42][43][44][45] have been performed. Furthermore, some REMPI coupled velocity map imaging (VMI) studies have been performed on the hydrogen halides, highlighting various photoionization and photofragmentation pathways.…”

“…These have recently been revisited with an emphasis placed on new observations as well as state interactions between Rydberg and valence (ion-pair and repulsive) states. 44,45 Among recent findings, the utilization of perturbation effects was used to illuminate interactions between an ion-pair state and a state that was "hidden" from REMPI detection. 45 The "hidden" state could either be a non-observable state due to selection rules or a state experiencing weak transition probabilities, which could possibly be detectable by other means, such as in standard absorption.…”