Optical Frequency Comb Fourier Transform Spectroscopy of ${}^{14}$N${}_2$${}^{16}$O at 7.8 μm

Abstract

We use a Fourier transform spectrometer based on a compact mid-infrared difference frequency generation comb source to perform broadband high-resolution measurements of nitrous oxide, ${}^{14}$N${}_2$${}^{16}$O, and retrieve line center frequencies of the $\nu$${}_1$ fundamental band and the $\nu$${}_1$ + $\nu$${}_2$ - $\nu$${}_2$ hot band. The spectrum spans 90 cm${}^{-1}$ around 1285 cm${}^{-1}$ with a sample point spacing of 3 $\times$ 10${}^{-4}$ cm${}^{-1}$ (9 MHz). We report line positions of 72 lines in the $\nu$${}_1$ fundamental band between P(37) and R(38), and 112 lines in the $\nu$${}_1$ + $\nu$${}_2$ - $\nu$${}_2$ hot band (split into two components with e/f rotationless parity) between P(34) and R(33), with uncertainties in the range of 90-600 kHz. We derive upper state constants of both bands from a fit of the effective ro-vibrational Hamiltonian to the line center positions. For the fundamental band, we observe excellent agreement in the retrieved line positions and upper state constants with those reported in a recent study by AlSaif et al. using a comb-referenced quantum cascade laser [J Quant Spectrosc Radiat Transf, 2018;211:172-178]. We determine the origin of the hot band with precision one order of magnitude better than previous work based on FTIR measurements by Toth [http://mark4sun.jpl.nasa.gov/n2o.html], which is the source of the HITRAN2016 data for these bands.

References in corpus (1)

• Molecular fingerprint-region spectroscopy from 5-12 μm using an orientation-patterned gallium phosphide optical parametric oscillator

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