A PROGRAM FOR FITTING SPECTRA WITH INTERACTING VIBRATIONS AND SPINS
H. M. Pickett · The Knowledge Bank (The Ohio State University) · 1988
A program has been developed for fitting rotation-vibration spectra with interacting vibrations and spins. Currently the program can handle up to 9 vibrational states and up to 4 spins with a variety of general interaction terms. The structure of the input and output of the program will be described along with some organizational details. Selection of algorithms for partioning the Hamiltonian and calculating the operators required particular care so that the code was general yet testable. One problem which caused considerable trouble was the selection of quantum number assignments for eigenvalues. Since quantum numbers for non-conserved quantities are only approximate, there is always some ambiguity. Nonetheless, a choice has to be made which is consistent with conventional use among spectroscopists. The difficulties with simple eigenvalue or eigenvector assignment approaches will be outlined, along with the approach selected for the program. This latter approach involves assignment to Wang blocks by 'least ambiguous projection', followed by energy ordering within a Wang block. In some cases, higher K states must be forced to have monotonically increasing first-order energy so that energy ordering will be correct.