Interaction of vibrational fundamental and combination states of ethylene in the 3 mu m region

High-resolution IR spectra of ethylene cooled in a molecular jet have been investigated revealing perturbations of some rovibrational lines of nu(9) and nu(11) fundamentals due to resonant Coriolis interactions. In the range of J up to 4, two combination states, nu(3) + nu(8) + nu(10) and nu(6) + nu(8) + nu(10), were shown to be the strongest local perturbers. Borrowing of dipole moments due to third-order Coriolis interaction was observed and the appropriate rovibrational lines of the combination bands were assigned. Modeling of the observed spectra was achieved using the power expansion of the Hamiltonian and the dipole moment operator in the frame of tensorial formalism of the symmetry point group of the molecule. The coupling of 32 vibrational combination states with the nu(9) and nu(11) fundamentals via cubic anharmonicity and Coriolis interaction was considered. Many new coupling parameters have been determined. (C) 1997 Academic Press.