First detection and analysis of the 3ν1 + ν2 + ν3 band of NO2 by CRDS near 6156 cm−1

Abstract

The high-sensitivity absorption spectrum of the NO2 molecule is recorded for the first time by cavity ring down spectroscopy between 6100 and 6200cm−1 with noise equivalent absorption αmin≈1×10−10cm−1. The spectrum is formed by weak rovibrational transitions belonging to the (311)-(000) band and the very weak (023)-(000) band at 6155.85 and 6183.92cm−1, respectively. In total, about 1881 rovibrational transitions are assigned. Upper energy levels with rotational quantum numbers N and Ka up to 49 and 8, and 30 and 3 are derived for the (311) and (023) vibrational states, respectively. Experimental line positions are modeled within an rms deviation of 0.0027cm−1 using the effective Hamiltonian approach which takes explicitly into account the spin-rotation interaction. Interpolyad resonance coupling between the (311) and (023) states as well as interactions involving the (311) state and two nearby dark states – (330) and (042) – were taken into account. The main parameters in the transition moment series are determined from a fitting of experimental intensities for the (311)-(000) and (023)-(000) bands.