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Physical Review A

Polarization effects on the two-photon dissociation of HD+ with two radiation fields in the presence of one and two intermediate resonant states

Banani Datta, Santanu Bhattacharyya

Published Sep 1, 1993• 2 citations
Publisher

Abstract

The polarization dependence of resonant two-photon dissociation characteristics has been investigated for ${\mathrm{HD}}^{+}$ excited from the ground state by two fields of different frequencies. The change in dissociation probability with field intensity and the dissociation line shape have been shown in the case of a single intermediate resonance for all possible combinations of polarizations. The photofragment energy spectra and the branching ratio between two possible continuum-energy states have been investigated for these polarization states when two intermediate resonances are present.

DOI
10.1103/physreva.48.2153

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The polarization dependence of resonant two-photon dissociation characteristics has been investigated for HD+{\mathrm{HD}}^{+}HD+ excited from the ground state by two fields of different frequencies. The change in dissociation probability with field intensity and the dissociation line shape have been shown in the case of a single intermediate resonance for all possible combinations of polarizations. The photofragment energy spectra and the branching ratio between two possible continuum-energy states have been investigated for these polarization states when two intermediate resonances are present.
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We present the effects of frequency chirping of laser pulses on (1+1)-photon resonance-enhanced dissociation dynamics of H2.{\mathrm{H}}_{2}.H2​. The dissociation occurs via two closely spaced nonadiabatically coupled intermediate levels which are in one-photon resonance or near resonance with the initial level. Predissociating levels embedded into continua are considered. When the first laser field is sufficiently intense and suitably chirped, the dissociation probability is enhanced by adiabatic rapid passage through the avoided crossing arising from the frequency swept radiative interaction. The whole population of the ground level can be effectively transferred to the intermediate levels by this technique facilitating the dissociation process by the second field. We also report the effect of frequency detuning and chirp width on the dissociation probability. Widths of the two peaks of the dissociation line shape increase with an increase in chirp width, resulting in the possibility of control in the dissociation yield. When the first field is a laser pulse of low intensity and constant frequency and the second laser frequency is chirped, predissociating levels take important parts in the dissociation dynamics and we obtain a signature of the nonadiabatic effect of the first step on the second step of photodissociation dynamics. This feature is due to the presence of the predissociating levels and the nonadiabatic mixing of two intermediate levels. All these results can be explained in terms of the adiabatic dressed levels.
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A theory of molecular photofragmentation is developed for coherent and incoherent light and for the case where dissociation lifetimes of field-induced resonances are shorter than pulse lengths. Using a mixed representation for the transition operator (a description of the initial state of the field with the coherent representation and of the final state with the number representation), we show how observables are modified at different field regimes by Poisson distributions. Applications to H2+{\mathrm{H}}_{2}^{+}H2+​ and D2+{\mathrm{D}}_{2}^{+}D2+​ are presented and discussed. They include line shapes and final distributions of kinetic energies for weak, intermediate, and strong fields. Results show that the interference of resonance states plays an important role even after averages over the field phases have been carried out to account for incoherent effects.