Vibrational state controlled bond cleavage in the photodissociation of isocyanic acid (HNCO)

Journal Article · Thu Jun 01 04:00:00 EDT 1995 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.468835· OSTI ID:46415

Brown, S S; Berghout, H L; Crim, F F ^[1]

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1. Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States)

We report the bond selected photodissociation of isocyanic acid (HNCO). This molecule dissociates from its first excited singlet state, breaking either the N--H bond to form H+NCO ({ital X} {sup 2}{Pi}) or the C--N bond to form NH ({ital a} {sup 1}{Delta})+CO ({sup 1}{summation}{sup +}). The threshold for production of NH lies about 3900 cm{sup {minus}1} above that of NCO, and we detect both of these channels by laser induced fluorescence on either the NH or the NCO fragment. Dissociating the molecule out of a vibrationally excited state on its ground electronic surface containing four quanta of N--H stretch (4{nu}{sub 1}) enhances the efficiency of the NCO channel over the NH channel by a factor of at least 20. We reach this conclusion by comparing the results of such a vibrationally mediated photodissociation experiment to those from a conventional single photon dissociation at the same total energy (about 1000 cm{sup {minus}1} above the threshold for the NH channel). Our estimate of the branching ratio in the one photon dissociation at this energy is roughly {Phi}{sub NCO}/{Phi}{sub NH}{approx}20, and it grows to {Phi}{sub NCO}/{Phi}{sub NH}{ge}400 in the vibrationally mediated photodissociation.

• OSTI ID: 46415
• Journal Information: Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Journal Issue: 21 Vol. 102; ISSN JCPSA6; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
BRANCHING RATIO
CHEMICAL BONDS
DISSOCIATION ENERGY
EXCITATION
FLUORESCENCE SPECTROSCOPY
HYDROCYANIC ACID
INFRARED SPECTRA
VIBRATIONAL STATES