Distribution of internal states of OH (X 2Π) from photodissociation of nitric acid

We detected fluorescence of OH (A 2Σ+−X 2Π) from nitric acid photolyzed at 193 nm. Transitions for spin-orbit states are resolved; the population ratio of these states is Π32/Π12 ≈ 1.1 ± 0.1. About 3% of available energy is distributed to rotation of the OH fragment; no vibrationally excited OH was observed. The transitional energies of OH and NO2 are estimated from the Doppler widths to be 2332 and 861 cm−1, respectively. These results indicate about 87.8% of the excess energy to be directed to internal energy of NO2. The experimental data indicate that NO2 may be produced in an electronically excited state.