ExoMol line lists – LX. Molecular line list for the ammonia isotopologue 15NH3

Abstract

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 10 000 cm$^{-1}$ ($\lambda \ge 1$ μm) 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 (Measured Active Rotation Vibration Energy Level) procedure. To this end, 37 experimental sources of the line positions of $^{15}$NH$_3$ available in the literature are collected, combined, and systematized to produce a self-consistent spectroscopic network of 21 095 $^{15}$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 53 856 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.