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Local mode and normal mode interpretations of the CH and CD stretching vibrational manifolds in C2H4 and C2D4

1988; American Institute of Physics; Volume: 89; Issue: 7 Linguagem: Inglês

10.1063/1.454806

1520-9032

J.L. Duncan, A. M. Ferguson,

Quantum, superfluid, helium dynamics

The CH and CD stretching vibrational manifolds in C2H4 and C2D4 have been studied up to six and four quanta of excitation, respectively. They are interpreted in each case in terms of a minimum number of local mode parameters. In C2H4, perturbations arising from Fermi resonances are complex and involve both the C=C stretching and the CH2 scissoring vibrations, with the former itself being in close resonance with the in-phase CH2 rocking overtone. Nevertheless, once all major resonances are taken into account, a self-consistent set of vibrational parameters is determined, which reproduces observations well in both infrared and Raman spectra. In C2D4, no significant Fermi resonance complications are apparent, spectroscopic interpretation is straightforward, and approximations inherent in the simple local mode model may be tested. The local mode parameters determined for C2H4 and C2D4 obey closely their expected isotopic interdependences. Values determined for the interbond harmonic coupling parameters in each case are in excellent agreement with those predicted through the harmonic force constants of ethylene.