Selective OD bond dissociation of HOD: Photodissociation of vibrationally excited HOD in the 5νOD state

Abstract

Exclusively selective OD bond dissociation of HOD has been demonstrated by the ultraviolet photodissociation at 243.1 nm through the fourth overtone state of the OD stretching mode (5nu(OD)). Branching ratio between the OH and OD bond dissociation channels has been determined by detecting H and D atoms, utilizing a (2+1) resonance-enhanced multiphoton ionization (REMPI) process. The OD bond dissociation has been solely observed with the branching ratio phi(D+OH)/phi(H+OD)>12, which has been determined by the detection limit for the H atom. Time-dependent wave-packet calculations reveal two important features for the highly selective OD bond dissociation: (1) strong local-mode character of the 5nu(OD) state and (2) limitation of the total excitation energy lower than the saddle point between the OH and OD dissociation channels in the A state. Additionally, the recoil velocity and angular distribution of the nascent D atom are roughly evaluated by analyzing the Doppler-resolved REMPI spectrum. Based on these results, the dynamics of the selective OD dissociation has been discussed in detail.

Selective control of HOD photodissociation using CW lasers

“…[33][34][35] As can be seen from the inset, there is a cross-talk between the two surfaces, even for the low intensity CW laser field employed here. The assumption of field induced instantaneous transport of the molecule to the excited surface with no role for cross-talk between the two surfaces in the dynamical outcome [8][9][10]12,13,16,23,26,[30][31][32] is not borne out by results of figure 1. In figure 2, where we have mapped the population dynamics and flow in detail.…”

“…[8][9][10][12][13][14][15][16][17][18][22][23][24]29 In case of selective dissociation of the O-D bond via transition to the repulsive first excited surface, prior excitation in the O-D stretch has been necessary. 10,12,18,20,21,31,[33][34][35] Most of the theoretical approaches to selective control of HOD photodissociation have used δ-function or very narrow Gaussian pulses with more or less instant transition of the molecule from ground to the repulsive excited surface. 9,10,12,18,29,30 This precludes any cross-talk between the two surfaces and the large frequency band width of these narrow pulses does not permit analyses based on manipulation of individual vibrational levels.…”

Selective photodissociation of O–H and O–D bonds from ground vibrational state of HOD using simple UV pulses

“…In the case of selective dissociation of the O-D bond via transition to the repulsive first excited surface, prior excitation in the O-D stretch has been necessary. 10,12,18,20,21,27,29,30 The second excited B ͑ 1 A 1 ͒ surface is much more anisotropic with a potential minimum at the linear configuration which is significantly displaced vis-a-vis the minimum in the ground surface. Excitation to this surface, therefore, immediately opens the bending angle 34,35 under the influence of a strong torque, and a full three dimensional ͑3D͒ treatment including the bending mode becomes necessary.…”

“…Based on the demonstrated separability of the bending mode from the stretching modes 31,32 and absence of a bending progression in the Raman spectrum, 33 most approaches to selective dissociation of O-H and O-D bonds have been two dimensional ͑2D͒ with the bending angle frozen at the equilibrium bond angle. Although considerable selectivity in dissociation of the O-H bond has been demonstrated without prior vibrational excitation of the O-H bond, [8][9][10][11][12]20,[26][27][28][29][30] in most cases, prior excitation [8][9][10][11][12][13][14][15][16][17][18][22][23][24][25] of the O-H bond to ensure its deposition in the H+O-D channel on transition to the repulsive à ͑ 1 B 1 ͒ surface has been the more favored route. In the case of selective dissociation of the O-D bond via transition to the repulsive first excited surface, prior excitation in the O-D stretch has been necessary.…”

Communication: Mode-specific photodissociation of vibrationally excited pyrrole

“…12 Excitation in a specific vibrational mode and, moreover, localization and preservation of energy until the excited molecule interacts with photons, could be foreseen for small molecules. Indeed, since the pioneering theoretical predictions [13][14][15] on photodissociation of vibrationally excited water with a single deuterium label, HOD, intensive experimental studies [16][17][18][19][20] were performed in attempt to control product identity or to obtain enhanced reactivity. For example, it has been shown that the OH bond dissociation is largely enhanced by dissociating HOD initially excited with four OH stretch quanta.…”