Mode-selective bond fission: Comparison between the photodissociation of HOD (0,0,1) and HOD (1,0,0)

Abstract

The 193 nm photodissociation of individual rotational levels of HOD molecules excited with one quantum of O–H or O–D 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) (O–H stretch) or (1,0,0) (O–D stretch) vibrationally excited HOD. The OD and OH fragments are detected by laser-induced fluorescence. In the photodissociation of HOD (0,0,1), the yield of both fragments is enhanced [relative to HOD (0,0,0)], but the yield of OD is increased 2.5±0.5 times more than that of OH. In the photodissociation of HOD (1,0,0), no enhancement of the yield of the fragments is obtained. Our results show that even the very lowest possible level of vibrational excitation can be ‘‘leveraged’’ to effect selective bond breaking. Also, these results demonstrate that bond cleavage does not necessarily occur on the weakened bond and they agree with theoretical calculations indicating that the yield of OD and OH fragments depends on the Franck–Condon overlap of the vibrational wave function with the repulsive surface of the upper state.

Cluster-induced photochemistry of CH3I at 248 nm

“…This chemistry would involve the processes (C) and (CH31)2-+C2H6 + 1 2 , (D) These are exoergic by -140 and -520 kJ Imol, respectively, assuming a dimer binding energy of 12 kJ/mol. 41 Our experimental result of very "cold" rotational and vibrational distribution of the 12 product could be consistent with a fourcenter concerted reaction, such as that shown in reaction (D). Although ground state four-center exchange reactions are forbidden by the Woodward-Hoffmann rules, the excited electronic state reaction is allowed.…”

Photodissociation of highly vibrationally excited NH3 in the 5νN–H region: Initial vibrational state dependence of N–H bond dissociation cross section

“…One of the remarkable examples is a bond-selected photodissociation of HOD molecule. [5][6][7][8][9][10] Crim and co-workers showed that the photolysis of HOD in the 4 O-H band produces OD fragments with at least 15 times higher yield than OH fragments. 5,7 On the other hand, Rosenwaks and coworkers reported that HOD molecules in the 3 O-D vibrational state preferentially photodissociate through the OHϩD channel.…”

Photodissociation of HOD (νOD=3): Demonstration of preferential O–D bond breaking

“…However, localizing excitation in the reaction coordinate, on a practical time scale, is difficult because of extensive intramolecular state mixing. Nevertheless, successful examples of selectivity have been achieved following excitation of localized ultraviolet ͑UV͒ chromophores, 1 photoisomerization, 2 site specific photolysis of haloalkanes, 3 and vibrational excitation in H 2 O, 4 -7 HOD, 8,9 and D 2 O. 10 The water and its isotopically substituted analogs are particularly suitable for photodissociation studies since they comprise several different vibrational modes.…”