DISTRIBUTIONS OF ROVIBRATIONAL STATES OF SECONDARY PRODUCT NO X-2-PI FROM PHOTODISSOCIATION OF NITRIC-ACID AT 193 NM

The distributions of vibrational, rotational, spin-orbit and lambda-do ublet states of nascent NO are obtained using: the A (2) Sigma-X (II)- I-2 transition via the technique of laser-induced fluorescence. NO is produced mainly from secondary dissociation of fragment NO2 from nitri c acid after photolysis at 193 nm. According to the measured distribut ion the partition of energy in NO X (II)-I-2 is calculated to be simil ar to 840 cm(-1) in vibration and similar to 1410 cm(-1) in rotation. The spin-orbit state (II1/2)-I-2 Of NO is populated about twice of tha t in (II3/2)-I-2 for the vibrational levels upsilon=0, 1, and 2. The m easured populations of vibrational states upsilon=0, 1, and 2 are 0.75 , 0.19, and 0.07, respectively; these populations agree with results c alculated with the statistical model, prior theory. The distributions of rotational states of NO X (II)-I-2 for these three vibrational leve ls have single maxima of Gaussian shape. The experimental data indicat e that although NO2, produced photochemically from nitric acid, was pr oposed to be in an electronically excited state, the state distributio ns of NO from unstable NO2 agree with chose from NO2 excited with mono chromatic light in the UV-vis range after averaging for a broad distri bution of internal energy. In the UV-vis range of excitation the NO fr agment dissociates from the ground electronic surface of NO2. Hence, t his unknown electronic state of NO, is expected to be coupled to the g round electronic surface then leading to dissociation. (C) 1997 Americ an Institute of Physics.