ExoMol line lists - III. An improved hot rotation-vibration line list for HCN and HNC

A revised rotation-vibration line list for the combined hydrogen cyanide (HCN)/hydrogen isocyanide (HNC) system is presented. The line list uses ab initio transition intensities calculated previously and extensive data sets of recently measured experimental energy levels. The resulting line list has significantly more accurate wavelengths than previous ones for these systems. An improved value for the separation between HCN and HNC is adopted, leading to an approximately 25 per cent lower predicted thermal population of HNC as a function of temperature in the key 2000 to 3000 K region. Temperature-dependent partition functions and equilibrium constants are presented. The line lists are validated by comparison with laboratory spectra and are presented in full as supplementary data to the article and at www.exomol.com

An experimentally-accurate and complete room-temperature infrared HCN line-list for the HITRAN database

A hydrogen cyanide line list (MOMeNT-90) developed for the HITRAN spectroscopic database covering 0–7500 cm−1 range (λ>1330 nm) is presented. The line list is a combination of the variationally calculated line intensities with line centers obtained from experimentally derived energy levels. There are four features of this line list which distinguishes it from the previously calculated ones. First, the intensities are variationally calculated using a new, high-accuracy potential energy surface (PES) obtained via fitting the PES using experimental energy levels. Second, a new ab initio dipole moment surface was calculated at a high level of quantum chemical theory. Based on the wave functions calculated with the new PES and use of the new dipole moment surface, line intensities are reported which of similar accuracy to those obtained experimentally. Third, the calculated states are mapped to the existing complete set of experimental eigenenergies, resulting in an assigned and complete HCN line list down to the HITRAN intensity threshold of 10−34 cm/molecule. Fourth, extensive validation of the line list is provided through line-by-line comparisons of the results with measured HCN spectra which confirms the accuracy of the intensities used to construct the line list. The line list is augmented with parameters needed to calculate line widths for pressure-dependent simulations