Assigning quantum labels to variationally computed rotational-vibrational eigenstates of polyatomic molecules.
A procedure is investigated for assigning physically transparent, approximate vibrational and rotational quantum labels to variationally computed eigenstates. Pure vibrational wave functions are analyzed by means of normal-mode decomposition (NMD) tables constructed from overlap integrals with respect to separable harmonic oscillator basis functions. Complementary rotational labels J(K(a)K(c)) are determined from rigid-rotor decomposition (RRD) tables formed by projecting rotational-vibrational wave functions (J not equal 0) onto products of symmetrized rigid-rotor basis functions and previously computed (J=0) vibrational eigenstates. Variational results for H(2)O, HNCO, trans-HCOD, NCCO, and H(2)CCO are presented to demonstrate the NMD and RRD schemes. The NMD analysis highlights several resonances at low energies that cause strong mixing and cloud the assignment of fundamental vibrations, even in such simple molecules. As the vibrational energy increases, the NMD scheme documents and quantifies the breakdown of the normal-mode model. The RRD procedure proves effective in providing unambiguous rotational assignments for the chosen test molecules up to moderate J values.
Mátyus
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Laboratory of Molecular Spectroscopy, Institute of Chemistry, Eötvös University, P.O. Box 32, H-1518 Budapest 112, Hungary.
Fábri
Csaba
C
Szidarovszky
Tamás
T
Czakó
Gábor
G
Allen
Wesley D
WD
Császár
Attila G
AG