High sensitivity cavity ring down spectroscopy of the 4ν3 band of NO2 near 1.59 µm

Abstract

The very weak 4ν3 B-type absorption band of the nitrogen dioxide main isotopologue (14N16O2) is investigated between 6175 and 6350 cm−1. The absorption spectrum of this band was recorded by high sensitivity continuous wave-cavity ring down spectroscopy with noise equivalent absorption of αmin ≈ 1 × 10−10 cm−1. More than 1630 lines of the 4ν3 band are assigned with rotational quantum numbers N and Ka up to 55 and 7, respectively, what corresponds to 1731 spin-rotation-vibration transitions. The overall measured set of the line positions is used to fit the effective Hamiltonian parameters. The effective Hamiltonian takes explicitly into account the Coriolis interactions between the spin rotational levels of the (0,0,4) vibrational state and those of the nearby (0,2,3) bright state at 6183.61 cm−1 together with the electron spin-rotation interactions. The fitted set of the parameters reproduces the observed line positions with an rms of 2.2 × 10−3 cm−1. A selected set of the measured line intensities are used to determine the effective dipole moment parameters including the Herman–Wallis type parameters describing the line intensities of the 4ν3 band. The rms deviation of the fit is 5.7%.