The 3 #nu#_1 overtone band of trans-nitrous acid: Rotational and perturbation analysis and absolute intensity

摘要

High-resolution (0.013 cm~-1) spectra of the second overtone of the OH stretch of trans-nitrous acid were recorded between 10 230 and 10 350 cm~-1. The spectra were analyzed to yield a complete set of rotational parameters, including the A, B, and C rotational constants and the 5 quartic distortion constants. Two groups of anharmonic perturbations were observed and analyzed, and for one of these groups, the spectra were fit with a second model to extract an improved set of parameters that took into account these interactions. Much less information could be obtained from our spectra about the second group of perturbations, except that the same dark vibrational state was probably not responsible for both groups of perturbations. The anharmonic coupling matrix element between the 3 #nu#_1 "bright" state and one "dark" vibrational state was found to be 0.0338(31) cm~-1, and possible assignments for the "dark" level are discussed. In addition, we report the first measurement of the absolute intensity of the 3 #nu#_1 overtone band, which was found to be 2.1+-0.6*10~-21 cm~2molecule~-1 cm~-1. Our findings are discussed in the context of the contribution of overtone-mediated processes to OH radical production in the upper atmosphere.