Direct observation of preferential bond fission by excitation of a vibrational fundamental: Photodissociation of HOD (0,0,1)

Abstract

The 193 nm photodissociation of individual rotational levels of HOD molecules excited with one quantum of O–H stretching vibrational energy is described. Stimulated Raman excitation and coherent anti-Stokes Raman scattering are used to prepare and detect, respectively, the (0,0,1) vibrationally excited HOD. The OD and OH fragments are detected by laser induced fluorescence. The photodissociation of the HOD (0,0,1) molecules yields at least three times more OD than OH.

Isotope effects in the photofragmentation of symmetric molecules: The branching ratio of OD∕OH in water

“…[5][6][7][8][9][10][11][12] Spurred by this interest we will in this paper analyze the origin of the "natural" branching ratio ͑to be defined below͒ for this reaction. In the following, P H ͑P D ͒ denote the probability for the upper ͑lower͒ reaction in Eq.…”

Two-pulse laser control of bond-selective fragmentation

“…If, e.g., an excited OH eigenstate is populated in HOD, an enhanced branching into the channel H ϩ OD is observed in a subsequent photodissociation process. [7][8][9][10][11] However, the branching ratio between H ϩ OD and D ϩ OH depends on the frequency of the second laser and high selectivity can be obtained only in a narrow frequency region. This frequency region is broadened when the initial vibrational excitation is increased but is still relatively narrow even at high vibrational excitation.…”

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

“…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.…”