Knowledge Bank

The distributions of vibrational, rotational, spin-orbit and lambda-doublet states of nascent NO and OH are obtained using the A-X transition of both OH and NO via the technique of laser-induced fluorescence. NO is produced from the secondary dissociation of fragment $NO2$ from nitric acid after photolysis at 193 nm. About 3% of available energy is distributed to rotation of OH fragment; no vibrational excited OH was observed. It was found that about 87.7% of excess energy to be directed to the internal energy of fragment $NO2$. According to the measurement of internal state distributions of secondary product NO, the partition of energy in NO $X2\Pi$ is calculated to be $840cm-1$ in vibration and $1410cm-1$ in rotation. The spin-obit state $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Pi 1/2$ of NO is populated about twice of that in $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Pi 3/2$ for the vibrational levels v=0,1,2. The measured populations of vibrational states v=0, 1, 2 are 0.75, 0.19 and 0.07, respectively; these populations agree with result calculated with the statistical model, prior theory. The experimental data indicate that although $NO2$ photochemical from nitric acid, was proposed to be in an electronically excited state, the state distribution of NO from unstable $NO2$ agree with those from $NO2$ excited with monochromatic light in the UV-vis range after average for the brood distribution of internal energy. Hence this unknown electronic state of $NO2$ is expected to be coupled to the ground electronic surface then leading to dissociation.