High sensitivity Cavity Ring Down Spectroscopy of N2O near 1.22 μm: (I) Rovibrational assignments and band-by-band analysis

- High sensitivity Cavity Ring Down Spectroscopy of N2O, between 7915 and 8334 cm−1.
- About 3300 lines assigned to five N2O isotopologues in natural isotopic abundance.
- A total of 64 bands analysed, 49 of them being newly reported.
- Intra- and interpolyad perturbations identified for seven bands.
- Valuable data to improve the global modeling of the spectrum of nitrous oxide.

The absorption spectrum of nitrous oxide (N2O) in natural isotopic abundance has been recorded near 1.22 µm by Cavity Ring Down Spectroscopy using an External Cavity Diode Laser (ECDL) as light source. The room temperature recordings were performed at a pressure of 10.0 Torr in the 7915-8334 cm−1 spectral range (1.26-1.19 μm). The typical noise equivalent absorption of the spectra, on the order of αmin~2×10−11 cm−1, allowed for the detection of lines with intensities on the order of 5×10−29 cm/molecule.More than 3300 transitions belonging to 64 bands of five nitrous oxide isotopologues (14N216O, 14N15N16O, 15N14N16O, 14N218O and 14N217O) have been rovibrationally assigned on the basis of the predictions of the effective Hamiltonian models developed for each isotopologue. For comparison, only 13 bands were previously measured by Fourier Transform spectroscopy in the studied region. All identified bands belong to the ΔP=13 and 14 series of transitions, where P=2V1+V2+4V3 is the polyad number (Vi are vibrational quantum numbers). The line positions and intensities are provided for all assigned lines. The maximum deviations between the measured position values and those predicted by the effective Hamiltonian models are about 0.2 cm−1 for the main isotopologue but reach values larger than 1 cm−1 for the less abundant minor isotopologues.The band-by-band analysis led to the determination of the rovibrational parameters of a total of 62 bands. The typical rms value of the (νobs−νfit) differences is 0.7×10−3 cm−1. Among the 62 bands, 49 are newly measured, for 13 others the rotational analysis is significantly improved and extended. A few resonance perturbations due to intra- and inter-polyad couplings are identified and discussed.