DETERMINATION OF THE INTERNAL STATE DISTRIBUTION OF NO(X 2-PI) PRODUCED IN THE O(3P)+NH(X 3-SIGMA-) REACTION

The internal state distribution of the NO product from the O(3P) + NH(X3-SIGMA-) reaction has been determined from a laser fluorescence experiment in a cell at a total pressure of 60 mTorr. The O atom and the NH reagents were prepared in a microwave discharge in oxygen and by the two-photon 193 nm photolysis of ammonia, respectively. The NO product was observed in the vibrational levels v = 1-8 by laser fluorescence excitation in A 2-SIGMA+-X2-PI bands. The nascent vibrational state distribution was found to be monotonically decreasing vs increasing v. The v = 1 rotational state distribution, extrapolated back to zero photolysis-probe delay, could be parametrized as a 1130 +/- 50 K Boltzmann distribution. Very little of the available energy is found as internal excitation of the NO product. The O + NH --> H + NO reaction is expected to proceed by the formation and decay of a short-lived HNO complex. The observed NO vibrational state distribution is interpreted in terms of a Franck-Condon model involving the overlap of vibrational wave functions for the NO stretch coordinate in the HNO complex with those for vibration in the free NO product. The NO rotational state distribution is governed largely by kinematic constraints in this H + HL --> HH + L reaction, where H and L are heavy and light atoms, respectively.