Theoretical study of vibrational overtone spectroscopy and dynamics in methanol

Conference · Tue Dec 31 04:00:00 EST 1996

OSTI ID:437296

Halonen, L O; Lehmann, K K ^[1]

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1. Princeton Univ., NJ (United States)

Experimentally observed couplings between OH and CH stretching modes in the high overtone region has been modelled successfully in terms of a curvilinear internal coordinate Hamiltonian including harmonic coupling between anharmonic OH and CH stretching oscillators and cubic Fermi resonance kinetic and potential energy couplings between CH stretches and HCH bends. The Hamiltonian matrices have been setup in block diagonal forms including only resonant states. The potential energy parameters have been optimized by the least squares method using experimental vibrational term values as data. The OH/CH stretch interaction parameter obtained agrees well with the one calculated by perturbation theory from a published ab initio harmonic force field. The model has reproduced well experimental band origins in the OH stretching overtone region and it has provided assignments for the bending overtones in the CH stretching fundamental region. Finally, a unitary transformation is found from the internal coordinate representation to the corresponding normal coordinate representation providing a set of normal coordinate parameters like diagonal anharmonicity parameters, Darling-Dennison resonance constants and cubic Fermi resonance force constants. These results confirm the experimental finding of energy redistribution between the OH and CH stretching modes on 100 fs time scale at 5{nu}{sub OH}.

• OSTI ID: 437296
• Report Number(s): CONF-9606118--
• Country of Publication: United States
• Language: English

Related Subjects

40 CHEMISTRY
DYNAMICS
FERMI RESONANCE
HAMILTONIAN FUNCTION
LEAST SQUARE FIT
MATHEMATICAL MODELS
METHANOL
VIBRATIONAL STATES