Selective control of photodissociation in deutereted water molecule HOD

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

“…Our earlier investigations 29,30 have shown that single color pulses cannot preferentially dissociate the O-D bond from ground vibrational state, and prior excitation of the O-D bond is required for its selective dissociation. We have shown elsewhere 41 that mixing of states may be replaced by mixing of colors, and we have therefore extended our approach to examine if two color lasers may be used for preferential dissociation of the O-D bond.…”

“…The first and second excited potential energy surfaces of HOD are well separated and following an earlier work, we too have considered only the ground and the first excited potential energy surfaces [8][9][10]12,13,16,18,20,[23][24][25][26][28][29][30] with bending motion frozen at equilibrium bond angle ͑104.52°͒. For femtosecond pulses to be considered here, the rotational motion has been neglected.…”

“…We have used a spatial grid spanning r O-H / r O-D bond lengths between 1a 0 and 10a 0 discretized on a mesh with 128 grid points. As in our previous investigations, 29,30 we have used the Gaussian UV pulse 18 of the form E͑t͒ = 0.09a͑t͒cos t, where a͑t͒ = exp͓−␥͑t − t uv ͒ 2 ͔ with full width at half maximum ͑FWHM͒ = ͱ 4 ln 2/␥ and ⌬t = 1 a.u. of t Ӎ 0.0242 fs.…”

“…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.…”

“…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.…”