INTERNAL STATE DISTRIBUTIONS OF PRODUCT OH AND NO FROM PHOTODISSOCIATION OF NITRIC ACID AT 193 NM
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Date
1997
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Ohio State University
Abstract
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 $NO_{2}$ 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 $NO_{2}$. According to the measurement of internal state distributions of secondary product NO, the partition of energy in NO $X^{2} \Pi$ is calculated to be $840 cm^{-1}$ in vibration and $1410 cm^{-1}$ in rotation. The spin-obit state $^{3}\Pi_{1/2}$ of NO is populated about twice of that in $^{3}\Pi_{3/2}$ 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 $NO_{2}$ photochemical from nitric acid, was proposed to be in an electronically excited state, the state distribution of NO from unstable $NO_{2}$ agree with those from $NO_{2}$ excited with monochromatic light in the UV-vis range after average for the brood distribution of internal energy. Hence this unknown electronic state of $NO_{2}$ is expected to be coupled to the ground electronic surface then leading to dissociation.
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Author Institution: Department of Chemistry, National Tsing, Hua University