Abstract
The distributions of vibrational, rotational, spin-orbit and lambda-doublet states of nascent NO are obtained using the A 2 Σ-X 2 Π transition via the technique of laser-induced fluorescence. NO is produced mainly from secondary dissociation of fragment NO 2 from nitric acid after photolysis at 193 nm. According to the measured distribution the partition of energy in NO X 2 Π is calculated to be ∼840cm -1 in vibration and ∼1410cm -1 in rotation. The spin-orbit state 2 Π 1/2 of NO is populated about twice of that in 2 Π 3/2 for the vibrational levels υ=0, 1, and 2. The measured populations of vibrational states υ=0, 1, and 2 are 0.75, 0.19, and 0.07, respectively; these populations agree with results calculated with the statistical model, prior theory. The distributions of rotational states of NO X 2 Π for these three vibrational levels have single maxima of Gaussian shape. The experimental data indicate that although NO 2 , produced photochemically from nitric acid, was proposed to be in an electronically excited state, the state distributions of NO from unstable NO 2 agree with those from NO 2 excited with monochromatic light in the UV-vis range after averaging for a broad distribution of internal energy. In the UV-vis range of excitation the NO fragment dissociates from the ground electronic surface of NO 2 . Hence, this unknown electronic state of NO 2 is expected to be coupled to the ground electronic surface then leading to dissociation. © 1997 American Institute of Physics.