HOT NH₃SPECTRA FOR ASTROPHYSICAL APPLICATIONS

Abstract

We present line lists for ammonia (NH 3 ) at high temperatures obtained by recording Fourier transform infrared emission spectra. Calibrated line lists are presented for twelve temperatures (300 -1300• C in 100• C intervals and 1370and each line list covers the 740 -2100 cm −1 range, which includes the majority of the ν 2 umbrella bending mode region (11 µm) and the ν 4 asymmetric bending mode region (6.2 µm). We also demonstrate the useful technique of obtaining empirical lower state energies from a set of spectra recorded at different sample temperatures. Using our NH 3 spectra, we have estimated lower state energies (E Low in cm −1 ) and our values have been incorporated into the line lists along with calibrated wavenumbers (ν in cm −1 ) and calibrated line intensities (S ′ in cm/molecule) for each line. We expect our hot NH 3 line lists to find direct application in the modelling of planetary atmospheres and brown dwarfs.

MARVEL analysis of the measured high-resolution spectra of 14NH3

“…The data from room-temperature measurements are augmented by data from a number of warm (373 K) [31,46], hot (up to 1640 K) [129,135,137,138], and cold [93,148] spectra. Hot spectra are rich in high-J and hot-band transitions but often have significantly larger uncertainties and a much increased chance of misassignment and mislabelling.…”

Spectroscopy of planetary atmospheres in our Galaxy

“…The other molecules were simulated using HITRAN 2008 (Rothman et al 2013) line list cross sections) of a series of molecules of astrophysical and planetological relevance (BT2 for water (Barber et al 2006; Fig. 13), CDSD-4000 for CO 2 (Tashkun and Perevalov 2011), as well as some hot spectra for NH 3 (Hargreaves et al 2011;Yurchenko et al 2011;Zobov et al 2011;Fig. 13), HCN (Harris et al 2008;Mellau 2011) and CH 4 (Nassar and Bernath 2003;Thiévin et al 2008;Hargreaves et al 2012;Yurchenko et al, in prep.)).…”

Molecular opacities for exoplanets

“…We have results for ammonia for 800-2200 cm −1 at 0.01 cm −1 resolution recorded in emission in two spectral pieces for every 100 • C between 300 • C and 1300 • C plus 1370 • C (some 24 highresolution spectra each with 4000 (low T) to 12 000 lines (high T)) and have published a 'proof-of-principle' paper [32]. These spectra have been recorded with our Bruker IFS 125 HR Fourier transform spectrometer and an evacuated tube furnace source with a flowing ammonia sample (similar to Nassar & Bernath [8]).…”

“…By carefully merging our hot line lists with the HITRAN line list, we have created a dataset that can be used over 500-1700 K for 5-13 µm [32]. The final product is a set of 12 line lists (covering 300-1370 • C), and each entry in a particular list is a line position, line intensity and lower state energy.…”