ExoMol line lists -- LX. Molecular line list for the ammonia isotopologue ${}^{15}$NH${}_3$

Abstract

A theoretical line list for ${}^{15}$NH${}_3$ CoYuTe-15 is presented based on the empirical potential energy and ab initio dipole moments surfaces developed and used for the production of the ExoMol line list CoYuTe for ${}^{14}$NH${}_3$. The ro-vibrational energy levels and wavefunctions are computed using the variational program TROVE. The line list ranges up to 10000 cm${}^{-1}$ ($\lambda \ge 1$ $\mu$m) and contains 929 795 249 transitions between 1 269 961 states with $J\le 30$. The line list should be applicable for temperatures up to $\sim$1000 K. To improve the accuracy of the line positions, a set of experimentally-derived energy levels of ${}^{15}$NH${}_3$ is produced using the MARVEL procedure. To this end, 37 experimental sources of the line positions of ${}^{15}$NH${}_3$ available in the literature are collected, combined and systematised to produce a self-consistent spectroscopic network of 21095 ${}^{15}$NH${}_3$ transitions covering 40 vibrational bands ranging up to 6818 cm${}^{-1}$ and resulting in 2777 energy term values. These MARVEL energies are then used to replace the theoretical values in the CoYuTe-15 line list and also complemented by pseudo-MARVEL energies obtained by an isotopologue extrapolation using the previously reported MARVEL energies of the ${}^{14}$NH${}_3$ parent isotopologue of ammonia. A list of 53856 high resolution transitions between MARVEL states and theoretical intensities is provided in the HITRAN format. Comparison with the recent experimental spectra of ${}^{15}$NH${}_3$ illustrate the potential of the line list for detections and as an efficient assistant in spectroscopic assignments. The line list is available from www.exomol.com.

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