Laser-initiated half-reaction. Vibrational and rotational state distribution of NO produced from the reactant pair O(1D)⋅N2O

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Abstract
The vibrational and rotational state distribution was measured for NO produced from the reaction O(1D)+N2O→2NO via a reactant pair O(1D)⋅N2O, which, in turn, formed by the 193 nm photolysis of the N2O dimer. The dimer was generated by the supersonic expansion through a pulsed nozzle. The distribution was determined by using the laser‐induced fluorescence of NO on its A–X transition. The rotational distribution was of the Boltzmann type characterized by a low temperature, 60–100 K, at each vibrational level measured. The vibrational distribution was found to be composed of the two components, one very cold and the other relatively hot. The experiment using an isotopically labeled N2O revealed that the vibrational energy was not equally distributed over two kinds of NO; the NO originally present in N2O was vibrationally cool while that formed from O(1D) and the terminal nitrogen of N2O was vibrationally hot. These results indicate that the reaction occurring is the abstraction of the terminal nitrogen by O(1D). The low rotational temperature, which sharply contrasts with the extremely high rotational excitation observed for the ordinary bimolecular reaction, can be rationalized by considering the geometrical difference in the encounter between the O(1D) atom and N2O. This fact, in turn, indicates that the product energy distribution is significantly affected by the orientation in the reactive encounter.

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