A reinvestigation of the NO3 1492 cm−1 band

Abstract

Ishiwata et al. [J. Chem. Phys. 8 2, 2196 (1985)] have recently observed an infrared diode laser spectrum of NO₃ in the 1492 cm⁻¹ region and have assigned it to the ν₃ band in the X̃²A^’₂ state. However, some of the derived constants such as the Coriolis coupling and spin–rotation constants did not conform well with expected values. In the present study, the observation was extended so as to take combination differences, which led us to revise the previous assignment slightly and to remove all the anomalies in the lower (i.e., ground) state. A most important result of the present study is that a spin–orbit interaction constant a_eff‖〈L_z〉‖ =0.17 cm⁻¹ is indispensable to explain the spin splitting observed for the upper state. The first‐order Coriolis coupling constant of the upper state (ζ=0.19) remains essentially the same as in the previous study and differs considerably from the value calculated for the ν₃ state (ζ=0.7). Possible explanations of these data are discussed in some detail to obtain more information on the molecular structure of the NO₃ radical.