THE NU(7)+NU(9)[-NU(7) HOT-BAND IN ETHYLENE STUDIED BY DOUBLE-RESONANCE TECHNIQUES

An IR-IR double resonance technique has been applied to an argon seeded molecular jet to perform hot band spectroscopy especially on the nu7 + nu9 <-- nu7 transition in ethylene. After excitation of a single rovibrational level by a CO2 waveguide laser, rotational states in the nu7 manifold are populated through collision induced rotational relaxation. Results are combined with data obtained from saturation dip spectroscopy in a 12 m long cell at room temperature. In total around 100 transitions have been newly assigned to the nu7 + nu9 <-- nu7 band. A least-squares fitting has been applied to all levels of nu7 + nu9, except two isolated and perturbed levels at K(a) = 6. A good statistical agreement has been obtained by taking into account a c-type Coriolis interaction with nu7 + 2nu10 + nu12, an a-type Coriolis interaction with nu2 + 2nu6 and a c-type Coriolis interaction with nu4 + nu9. Furthermore, earlier data on the nu10 + nu9 <-- nu10 hot band have been reexamined. The two hot band spectra have been compared to analyse the propensities of different relaxational pathways.