High sensitivity Cavity Ring Down Spectroscopy of the 2ν1 + 3ν2 + ν3 band of NO2 near 1.57 µm

Abstract

The weak 2ν1+3ν2+ν3absorption band of the nitrogen dioxide main isotopologue (14N16O2) is investigated near 6350cm−1. The absorption spectrum was recorded by high sensitivity Cavity Ring Down Spectroscopy with a noise equivalent absorption of αmin ≈ 1 × 10−10cm−1. In total, 1069 lines of the 2ν1 +3ν2 +ν3 band were assigned with rotational quantum numbers N and Ka up to 48 and 8, respectively, that corresponds to 1276 vibration-rotation transitions. The derived set of line positions is reproduced with an effective Hamiltonian with an rms of 2.35 × 10−3cm−1 for the (obs.-calc.) deviations. The effective Hamiltonian takes explicitly into account the Coriolis interactions between the spin rotational levels of the (2,3,1) upper vibrational state and those of two nearby dark states - (2,5,0) and (2,1,2) - together with the electron spin-rotation interactions. Using the corresponding eigenfunctions the principal effective dipole moment parameter responsible for the line intensities of the 2ν1 +3ν2 +ν3 band is fitted to selected measured line intensities which are reproduced with an rms deviation of 6.2%.