Superexcited state reconstruction of HCl using photoelectron and photoion imaging

Abstract

The velocity-map imaging technique was used to record photoelectron and photofragment ion images of HCl following two-photon excitation of the E Sigma(+)(0+), V 1Sigma(+)(0+) (nu=9,10,11) states and subsequent ionization. The images allowed us to determine the branching ratios between autoionization and dissociation channels for the different intermediate states. These branching ratios can be explained on the basis of intermediate state electron configurations, since the configuration largely prohibits direct ionization in a one-electron process, and competition between autoionization and dissociation into H* (n=2)+Cl and H+Cl*(4s,4p,3d) is observed. From a fit to the vibrationally resolved photoelectron spectrum of HCl+ it is apparent that a single superexcited state acts as a gateway to autoionization and dissociation into H+Cl*(4s). Potential reconstruction of the superexcited state to autoionization was undertaken and from a comparison of different autoionization models it appears most likely that the gateway state is a purely repulsive and low-n Rydberg state with a (4Pi) ion core.

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

“…13 The experiments were performed using the same linearly polarized laser pulse for the two-photon state preparation and the subsequent single-photon photodissociation of this prepared state. Two-photon rovibronic state selection was achieved using the Q-branch Jϭ1 transition to the E 1 ⌺ 0 state of HCl at 83772.0 cm Ϫ1 , and the H 1 ⌺ 0 state of HBr at 79643.0 cm Ϫ1 .…”

“…The effects of this prepared angular momentum polarization upon the observed vector correlations are pronounced and complicated. [12][13][14] Control over the prepared angular momentum polarization provides a powerful tool for the interrogation of the photodissociation dynamics, allowing for control over which electronic states are active in the photodissociation. 12,15 In essence, a state of known angular momentum polarization ͑and molecular axis alignment/orientation͒ allows for control over the molecular frame geometry in the laboratory frame and so control over the molecular frame transition dipole moment.…”

Multiphoton Ionization and Fragmentation of Hydrogen Chloride: A Diatomic Still Good for a Surprise

“…[22, Figure 3]), suggesting that the corresponding Cl partner fragment is formed in the excited 2 P 1/2 spin-orbit state. This behaviour contrasts the outcome of the dissociation via the 3 Π gateway state which yields mainly ground state 2 P 3/2 Cl atoms as partner fragments [3,19]. This unexpected observation was explained by the lower photon energies used in 3 Δ 2 excitation.…”

“…All three paths together result in the typical velocity image shown in Figure 3. H + ions resulting from the dissociation of superexcited HCl into H * (n = 2) + Cl and those resulting from autoionization followed by dissociation into H + + Cl, that is, path I and path III, proceed over the same "gateway" state shown in Figures 4 to 7, which was found to be a 3 Π 0 repulsive state in the Rydberg series converging to the ionic A 2 Σ + state [19].…”

“…Photoproduct spatial anisotropies and kinetic energy distributions were analyzed by Loock and coworkers [1,3,19] and by Gericke and co-workers [20,21] using velocity map imaging techniques. Both groups investigated the ionization/fragmentation pathways through various vibrational bands of the B 1 Σ + (0 + ) state.…”