Non-resonant vibrational excitation of HOD and selective bond breaking

Abstract

This paper reports a time-dependent quantum mechanical wave packet study for bond-selective excitation and dissociation of HOD into the H + OD and D + OH channels in the first absorption band. Prior to excitation, the HOD molecule is randomly oriented with respect to a linearly polarized laser field and accurate static dipole moment and polarizability surfaces are included in the interaction potential. Vibrational excitation is obtained with intense, non-resonant 800 nm few-cycle excitation using dynamic Stark effect/impulsive Raman scattering. Dissociation is accomplished by another ultrashort vacuum ultraviolet-laser excitation. A laser control scheme is designed with a train of simple, non-resonant laser pulses in order to enhance the selectivity between the fragmentation channels. The effect of the carrier-envelope-phase of the ultrashort laser pulses is also investigated.

Controlling Chemical Reactions with Laser Pulses

“…Thereby, first we consider the approach based on dynamic Stark control, where an ultrashort (3.5 fs) intense (10 14 W/cm 2 ) nonresonant (800 nm) laser pulse induces the vibrational dynamics of HOD in the ground electronic state which, when followed by a properly timed ultrashort (δ-pulse) excitation, undergoes a Franck–Condon transition to the dissociative first electronically excited state. 16 This will eventually help us to understand the extent of control that can be achieved with simple off-resonant vibrational pre-excitation. Moreover, the ease of realizing this two-pulse control scheme with any nonresonant laser pulse lends itself to convenient experimental implementation.…”

“…(See the discussion concerning photodissociation.) Reprinted from ref ( 16 ) with the permission of AIP Publishing.…”

“…The time axes indicate the time measured relative to the δ-pulse excitation. Reprinted from ref ( 16 ) with the permission of AIP Publishing.…”

“… a The time delay between the subpulses is 12.2 fs. Reprinted from ref ( 16 ) with the permission of AIP Publishing. …”

Coherent control of selective bond breaking: HOD in the A∼-state revisited

“…As a prototype of the chemically interesting scenario of bond-selective chemistry, the control of the branching ratio (in theÃ-state) between the two fragmentation channels in HOD (H+OD or D+OH) has been a matter of long-term interest [6,7,8,9,10,11,12,13,14,15]. To that end, we mention previous work assuming, oriented HOD molecules [10], the creation of a vibrational superposition state by an unspecified mechanism [11], or a scheme which required non-trivial pulse shaping of intense ultrashort vacuum-ultraviolet (VUV) pulses [14].…”