Low-temperature high-resolution absorption spectrum of ¹⁴NH₃ in the ν₁+ν₃ band region (1.51 μm)

Abstract

Jet-cooled spectra of ¹⁴NH₃ and ¹⁵NH₃ in natural abundance were recorded using cavity ring-down (CRDS, 6584–6670 cm⁻¹) and cavity enhanced absorption (CEAS, 6530–6700 cm⁻¹) spectroscopy. Line broadening effects in the CRDS spectrum allowed lines with J ^″-values between 0 and 3 to be identified. Intensity ratios in ¹⁴NH₃ between the jet-cooled CRDS and literature room-temperature data from Sung et al. (J. Quant. Spectrosc. Radiat. Transfer, 113 (2012), 1066) further assisted the line assignments. Ground state combination differences were extensively used to support the assignments, providing reliable values for J, K and inversion symmetry of the ground state vibrational levels. CEAS data helped in this respect for the lowest J lines, some of which are saturated in the CRDS spectrum. Further information on a/s doublets arose from the observed spectral structures. Thirty-two transitions of ¹⁴NH₃ were assigned in this way and a limited but significant number (19) of changes in the assignments results, compared to Sung et al. or to Cacciani et al. (J. Quant. Spectrosc. Radiat. Transfer, 113 (2012), 1084). Sixteen known and 25 new low-J transitions were identified for ¹⁵NH₃ in the CRDS spectrum but the much scarcer literature information did not allow for any more refined assignment. The present line position measurements improve on literature values published for ¹⁵NH₃ and on some line positions for ¹⁴NH₃.

Keywords:

• ammonia
• overtone spectroscopy
• jet cooled spectroscopy
• ultrasensitive detection

Acknowledgements

We thank Dr Cacciani (Lille) for useful discussions, Dr Yurchencko (UCLondon) for providing the Exomol line list and Drs Didriche and Vander Auwera as well as Mr Vanfleteren (ULB) for their help in the experiments and/or calibration procedure.

Additional information

Funding

This work was sponsored in Belgium by the Action de Recherches Concertées de la Communauté française de Belgique, the Region Bruxelles-Wallonie (Innoviris project) and the Foundation Wiener-Anspach, to which we are indebted. This work was supported by the Fonds de la Recherche Scientifique (F.R.S.-FNRS, Belgium); the Groupe de Recherche International (GDRI) HiResMIR (High resolution microwave infrared & Raman spectroscopy for molecules of atmospheric, planetologic and astrophysical interest). It was supported in Italy by the project PRIN2012 ‘Spettroscopia e Tecniche computazionali per la ricerca Astrofisica, atmosferica e Radioastronomia’ (STAR).