An improved analysis of the N2O absorption spectrum in the 1.18 µm window

A high-sensitivity absorption spectrum of natural nitrous oxide has been recorded at 10 Torr between 8321 and 8620 cm−1 (1.20 – 1.16 µm). The used cavity ring down spectrometer was referenced to a self-referenced frequency comb providing an accurate frequency scale of the spectra. The predictions of effective operator models were used for the line assignment. All identified bands correspond to the ΔP=14–16 series of transitions, where P = 2V1+V2+4V3 is the polyad number (Vi=1–3 are the vibrational quantum numbers). A total number of 3975 transitions belonging to the 14N216O, 14N15N16O, 15N14N16O,14N218O, and 15N216O isotopologues were measured with estimated accuracy better 1 × 10−3 cm−1 for most of the lines. Compared to the recent analysis of N2O spectra at 1 Torr recorded in the same region (Karlovets et al. JQSRT, 262 (2021) 107,508, doi: 10.1016/j.jqsrt.2021.107508), the higher pressure of the recordings and improved quality of the predictions have allowed to: (i) newly assign twenty-two bands, including the 4ν3 band of the 15N216O minor isotopologue, (ii) extend the assignments of previously known bands, (iii) determine the small self-induced pressure shifts of the two strongest bands (less than 10−4 cm−1) by difference of the line positions at 1 and 10 Torr and use them to obtain the zero-pressure value of the line positions, (iv) derive new or improved spectroscopic constants of 69 bands from the standard band-by-band analysis, and (v) analyze six local resonance perturbations affecting three bands, including the identification of a few extra lines due to intensity transfer. Finally, the comparison of the line positions and intensities with their predicted values and with available databases is discussed