(2+1) REMPI spectra of Ω=0 states of the hydrogen halides: Spectroscopy, perturbations and excitation mechanisms

Abstract

(2+1) REMPI spectra of HX (X=Cl, Br and I) have been recorded and analyzed by simulation calculations to derive rotational constants, band origins and isotope shift values for a number of vibrational bands of Ω=0 states. Our data for HCl compare nicely with those derived by Green et al. by conventional analysis methods [D. S. Green et al., J. Mol. Spectrosc. 150, 303, 354, 388 (1991); D. S. Green and S. C. Wallace, J. Chem. Phys. 96, 5857 (1992)]. New spectroscopic parameters were derived for eight vibrational bands which are assigned to the V(1Σ+) state, for v′=4 of the E(1Σ+) state, as well as for five new bands in HBr. New spectroscopic parameters were derived for four vibrational bands which are assigned to the V state and for v′=1 of the E state in HI. Anomalies observed in energy level spacings, rotational parameters and isotope shift values are interpreted as being largely due to homogeneous interactions between the V and the E states. It is argued that the interaction causes a compression of rovibrational levels in the E state manifold but an expansion of levels in the V state manifold, something which might be expected for a Rydberg to ion-pair interaction. Variations observed in the intensity ratio of O and S line series to Q line series in vibrational bands of the E and V states for HCl and HBr are discussed and mechanisms of two-photon excitation processes are proposed.

Measurement of Three-Dimensional Velocity Distributions of the Products of Cl2, NO, and HCl Photodissociation or Photoionization

“…The dye laser fundamental is first doubled and then focused into the mass spectrometer chamber. In this work, we obtained (2 + 1 i ) REMPI spectra [7,8] of a Cl atom (235.336 nm) and an HCl molecule (transitions at about 237 nm); (1 + 1 i ) REMPI spectra [9] of an NO molecule (about 226.2 nm); and (2+1+ 1 i ) and (2 + 1 i + 1) REMPI spectra [8,10] of H + and Cl + ions (the subscript index designates the ionizing photon): Here, v stands for vibrational and N and J, for rotational quantum numbers. It is worth noting that HCl + , Cl + , and H + ions are detected in processes (3)-(6).…”

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

“…DE J 0 , J 00 (i) is the difference in rotational energies in the ground and the excited states [1,7]. The band origin of an isotopomer i can be expressed as a function of the electronic term value of the excited state, T 0 e and the vibrational frequencies (in cm À1 ) of the two states involved ðx 0 e ðiÞ and x 00 e ðiÞÞ [4,9,11].…”

“…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.…”