Resonance enhanced multiphoton ionization of the hydrogen halides: Rotational structure and anomalies in Rydberg and ion-pair states of HCl and HBr

Abstract

͑2ϩ1͒ resonance enhanced multiphoton ionization spectra have been recorded, simulated, and used to derive energies of rovibrational levels in the F(1 ⌬), E(1 ⌺ ϩ), and V(1 ⌺ ϩ) states for HCl ͑H 35 Cl and H 37 Cl) and HBr ͑H 79 Br and H 81 Br). Spectroscopic parameters derived for the F states compare nicely with those derived by others using conventional analysis methods. Clear evidence for near resonance interactions between the F and the V states is seen for the first time, both in HCl and HBr. Shape of curves for rotational level energy spacings versus rotational quantum numbers are found to depend characteristically on the nature of off-resonance interactions observed between the E and the V states. Model calculations for state interactions, based on perturbation theory, are performed for HCl. These prove to be useful to interpret observed perturbations, both qualitatively and quantitatively. Interaction strengths are evaluated for F to V and E to V state interactions. Variations observed in the intensity ratios of O and S line series to Q line series in vibrational bands of the V state for HCl are discussed and mechanisms of two-photon excitation processes are proposed.

Two‐Photon Dissociation Spectroscopy of State‐Selected HCl+ and DCl+ Ions

“…[21][22][23][24] Kulp described the 2 P state of HCl + as an intermediate between Hund's cases (a) and (d), [1] while Norling discussed a combination of Hund's cases (a) and (b). [4] 6,7,8,9). From the analysis of the data, spectroscopic parameters of the X and the A states were derived (including the L-doubling in the X state and the spin-rotation coupling in the A state).…”

Three- and two-photon absorption in HCl and DCl: identification of Ω=3 states and state interaction analysis

“…A number of higher energy X = 3 (U) states for HBr were observed in cold supersonic expansions [5]. Three-and two-photon absorption spectroscopy has added to the rich spectroscopy of the hydrogen halides which is characterized by a wide variation in the strengths of Rydberg to ion-pair interactions as well as spin-orbit couplings arising from the halogen atoms [6,7,[12][13][14][15][16][17][18][19]. Furthermore, use of expressions for rovibrational line strengths in three-photon absorption [1,2] has been found to be useful to derive rotational population distributions in the ground states of HBr [2] and HCl [3] from (3 + 1)REMPI spectra.…”

“…Furthermore, use of expressions for rovibrational line strengths in three-photon absorption [1,2] has been found to be useful to derive rotational population distributions in the ground states of HBr [2] and HCl [3] from (3 + 1)REMPI spectra. The relative intensities of rotational line series have been used as evidence in debates about the effect of intermediate states on the mechanism of multiphoton processes in two- [6,7,20] and three-photon [2,4] absorptions to X 0 = 0 ‹ X 00 = 0 transitions in Br 2 [20], HBr [7], and HCl [2,4,6,7].…”

“…(n + 1)REMPI spectra of rotational structure in electronic transitions of diatomic molecules have been simulated successfully by taking account of the three-(n = 3) [1][2][3][4][5] and two-(n = 2) [6][7][8][9][10][11] photon transition probabilities only. This suggests that the final ionization step is largely wavelength independent and that the (n + 1)REMPI spectra (n = 2, 3) can be treated as n-photon absorption spectra to a first approximation.…”

“…Clear evidence for near resonance interactions between the j and the V ( 1 R + ) ion-pair states is seen both in the (3 + 1) and (2 + 1)REMPI spectra of HCl and DCl. The interaction strength is evaluated by model calculations [6], based on perturbation theory [21] and deperturbed energy levels [19].…”