Near-infrared band of the nitrate radical NO3 observed by diode laser spectroscopy

We have analyzed the near-infrared band of NO3 observed at 7602 cm(-1) by using diode laser spectroscopy. Most of the spectral lines were recorded using source-frequency modulation. Zeeman modulation was found useful in selectively detecting some Q branch lines, which provided us with a clue to the assignment of the observed spectra. The band satisfied selection rules for a parallel band and was thus ascribed to a (2)A(1) ''-(2)A(2)' vibronic component associated with the E-2 ''-(X) over tilde (2)A(2)' electronic transition, namely, to a transition from the ground vibronic state to the A(1) '' vibronic state resulting from excitation of the degenerate in-plane bending mode in the E-2 '' electronically excited state manifold. The band was almost free of perturbations, except for some K=6 lines. The least-squares analysis of 581 assigned lines led to molecular parameters of the upper state, where ground-state parameters were fixed to those obtained from the infrared study previously reported [K. Kawaguchi, E. Hirota, T. Ishiwata, and I. Tanaka, J. Chem. Phys. 93, 951 (1990)]. The upper-state B rotational constant gave the effective N-O distance of 1.271 Angstrom, which is to be compared with 1.240 Angstrom in the ground vibronic state. The epsilon(bb) spin-rotation interaction constant of the upper state was close in magnitude to that in the ground vibronic state, but of opposite sign. This observation indicates that the spin-rotation interaction is primarily caused by that between the E-2 '' excited and the ground electronic states. (C) 1997 American Institute of Physics.