A comparison of numerical and analytical approaches for reduction of rotational and vibration–rotational spectra of diatomic molecules to parameters of radial functions

The communication presents a numerical test of the three most popular methods used for direct inversion of the highly resolved IR and MW spectra of diatomic systems: (A) the numerical techniques such as those described by Coxon (J. A. Coxon and P. G. Hajigeorgiou, J. Mol. Spectrosc., 1991, 150, 1, ; J. A. Coxon, J. Mol. Spectrosc., 1992, 150, 274, ), Bernath (J. M. Campbell, M. Dulick, D. Klapstein, J. B. White and P. F. Bernath, J. Chem. Phys., 1993, 99, 8379, ; H. G. Hedderich, M. Dulick and P. F. Bernath, J. Chem. Phys., 1993, 99, 8363, ; M. Dulick, K. Q. Zhang, B. Guo and P. F. Bernath, J. Mol. Spectrosc., 1998, 188, 14, ), Le Roy (J. Y. Seto, R. J. Le Roy, J. Verges and C. Amiot, J. Chem. Phys., 2000, 113, 3067, ) and their co-workers; (B) the analytical approach developed by Ogilvie (J. F. Ogilvie, J. Phys. B, 1994, 27, 47, ); and (C) its improved version, called deformational self-consistent (DS-c) procedure, proposed by Molski (M. Molski, J. Phys. Chem., 1999, 103, 5269, ; M. Molski, Chem. Phys. Lett., 1999, 306, 88, ; M. Molski, Chem. Phys. Lett., 2001, 342, 293, ). The results obtained for the test molecule LiH X 1 Σ + indicate that the energy levels and radial parameters generated by Ogilvie's Radiatom program are not sufficiently accurate for use in external applications.