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