Ra. Brownsword et al., DISSOCIATION DYNAMICS OF HNCO AND DNCO AFTER LASER PHOTOEXCITATION INTHE VACUUM-ULTRAVIOLET, The Journal of chemical physics, 106(23), 1997, pp. 9563-9569
Using the laser photolysis-laser-induced fluorescence ''pump-probe'' t
echnique, the gas-phase dissociation dynamics of HNCO((X) over tilde (
1)A')+h nu-->H+NCO and DNCO((X) over tilde (1)A')+h nu-->D+NCO after p
hotoexcitation at the Lyman-alpha wavelength were studied under collis
ion-free conditions at room temperature. In the vacuum ultraviolet pho
todissociation experiments narrow band tunable Lyman-alpha laser radia
tion (lambda approximate to 121.4-121.6 nm) was used both to photodiss
ociate the parent molecules and to detect the produced nascent H and D
atom products via (2p P-2<--1s S-2) laser induced fluorescence. The f
ollowing quantum yields Phi(H-D) for H-D atom formation were determine
d by a photolytic calibration method: Phi(H)=(0.62+/-0.15) and Phi(D)=
(0.51+/-0.17). For HNCO and DNCO the measured H-D atom Doppler line sh
apes can be well described by a single Gaussian function, which corres
ponds to a statistical Maxwell-Boltzmann-like distribution of the tran
slational energy. From the measured H and D atom Doppler profiles the
average H and D atom kinetic energy was determined to be E-T(H)=(137+/
-10) kJ/mol and E-T(D)=(115+/-4) kJ/mol, respectively. The average kin
etic energies were found to be in reasonable agreement with results fr
om simple statistical calculations in which it is assumed that H-D ato
ms are produced in combination with NCO in the ground electronic state
((X) over tilde (2) Pi), A dissociation mechanism is suggested in whi
ch H-D atom formation proceeds via a statistical unimolecular decay of
a hot H-DNCO intermediate formed by a radiationless transition of the
optically excited bound H-DNCO state to a lower-lying dissociative st
ate. (C) 1997 American Institute of Physics.