Spin–orbit branching in the photofragmentation of HCl

Abstract

The dynamics of the photofragmentation of HCl and DCl, subsequent to A 1Π←X 1Σ+ electronic excitation, is treated exactly based on new multireference, configuration-interaction ab initio calculations of the relevant electronic potential energy curves and off-diagonal matrix elements. The calculated total cross section agrees well with both earlier calculations and experiment. By contrast, the relative cross sections for formation of the two accessible fine-structure channels [Cl(2P1/2) and Cl(2P3/2)] disagree with the most recent experimental results, and, more dramatically, with the results of prior theoretical predictions. Analysis of the redistribution of the photofragment flux, as a function of the H–Cl separation, reveals that the product branching is determined at relatively large HCl distances, considerably beyond the Franck–Condon region, and is governed by the spin–orbit coupling between the initially excited A 1Π state and the Ω=1 components of the a 3Π and 1 3Σ+ states.

Investigation on the photofragmentation of hydrogen chloride

“…The ab initio results for the excitation energies, E v and the oscillator strengths, f, for the corresponding states are listed in Table 2. As can be seen, the magnitude of the vertical excitation energies of the present work is in agreement with the former studies [24]. For the two fine structure states of Cl, P 3/2 and P 1/2 (spinorbit constant DE so = 0.109 eV), the X 1 R þ 0 , a 3 P 1 and A 1 P 1 states correlate to Cl ( 2 P 3/2 ), while the higher valence t 3 R þ 1 state, which begins to possess some Rydberg character, correlates with Cl * ( 2 P 1/2 ).…”

“…The available information on the associated transition dipole matrix, the permanent dipole moments, and the spin-orbit coupling curves was obtained from Ref. [24]. The equilibrium bond length of X 1 R þ 0 state is calculated to be 2.432 Bohr and agrees with experimental data [25] of 2.409 Bohr.…”

Two-photon state selection and angular momentum polarization probed by velocity map imaging: Application to H atom photofragment angular distributions from the photodissociation of two-photon state selected HCl and HBr

“…For two-photon excitation of HCl to the E Ј⌺ 0ϩ ϩ state at 2ϫ41 866.0 cm Ϫ1 , the dominant intermediate virtual state is expected to be the repulsive A 1 ⌸ 1 state that gives rise to the broad absorption feature centered at around 240 nm. 39,40 Absorption of a third photon at 41 866.0 cm Ϫ1 causes dissociation of HCl into H*(n ϭ2) and Cl( 2 P 1/2 ) as well as a second minor channel producing spin-orbit ground state Cl( 2 P 3/2 ). Other product channels are also observed but are not treated in this paper.…”

“…Assuming first a Hund's case ͑a͒ or ͑c͒ description, 39 a two-photon X 1 ⌺ 0 → 1 ⌺ 0 excitation may in principle proceed via virtual states at the one-photon level with either ⍀ϭ0 or ⍀ϭϮ1 character, corresponding to parallel and perpendicular transitions, respectively. These pathways for Q-branch excitation of J 0 ϭ1 may be represented as…”

Photodissociation of a HCl molecule adsorbed on ice at T=210K

“…In this study, we do not include the spin orbit interaction and consider only the electronic X 1 R + ground state and the A 1 Õ excited state. The intramolecular potential energy surface (PES) for the dissociating molecule is obtained by a spline on ab initio calculations from the gas phase values for both the ground and the excited states[46].2.3.2.2. Surface/adsorbate interaction potentials.The HClice interaction is written as the sum of pairwise potentials[12,47] including the electrostatic interaction between charges distributed on HCl and on the H 2 O molecules and the dispersion-repulsion energy between HCl's and H 2 O's atoms.…”