Analysis of the accuracy of calculations using Duo and Level diatomic nuclear motion programs

Analysis of the accuracy of two programs widely-used for computing ro-vibrational spectra of diatomic molecules, namely Duo and Level, is presented. Using model systems for which analytic results are available it is shown that compared to Level, Duo gives similar or usually higher accuracy for line intensities, and is accurate for calculations of bound state energies and corresponding wavefunctions. Furthermore, Duo provides matrix elements accurate to about relative to the analytic values, which is sufficient for developing of accurate methods for experimental determination of some macroscopic gas features, such as pressure, concentration, temperature, and so on; this level of accuracy can only be achieved with Level by significantly increasing the number of grid points in the calculation

High accuracy water potential energy surface for the calculation of infrared spectra

Transition intensities for small molecules such as water and CO$_2$ can now be computed with such high accuracy that they are being used to systematically replace measurements in standard databases. These calculations use high accuracy ab initio dipole moment surfaces and wavefunctions from spectroscopically-determined potential energy surfaces. Here an extra high accuracy potential energy surface (PES) of the water molecule (\hato) is produced starting from an ab initio PES which is then refined to empirical rovibrational energy levels. Variational nuclear motion calculations using this PES reproduce the fitted energy levels with a standard deviation of 0.011 \cm, approximately three times their stated uncertainty. Use of wavefunctions computed with this refined PES is found to improve the predicted transition intensities for selected (problematic) transitions. A new room temperature line list for H2(16)O is presented. It is suggested that the associated set of line intensities is the most accurate available to date for this species.Comment: 14 pages, 1 figure, 4 table

ExoMol line lists – L: high-resolution line lists of H3+, H2D+, D2H+, and D3+

New MiZo line lists are presented for the D2H+ and D$_3^+$ isotopologues of H$_3^+$. These line lists plus the existing H$_3^+$ MiZATeP and the Sochi H2D+ line lists are updated using empirical energy levels generated using the MARVEL procedure for H$_3^+$, H2D+ and D2H+, and effective Hamiltonian energies for D$_3^+$ for which there is significantly less laboratory data available. These updates allow accurate frequencies for far infrared lines for these species to be predicted. Assignments of the energy levels of H$_3^+$ and D$_3^+$ are extended using a combination of high accuracy variational calculations and analysis of transition intensities. All line lists are made available via www.exomol.com

PES15k potential energy surface from High-accuracy water potential energy surface for the calculation of infrared spectra

Fortran program for the PES15k potentia