A direct study of the vibrational bending effect in line mixing: The hot degenerate 11(1)0<-01(1)0 transition of CO2

The study of the isotropic Raman Q-branch of a hot band Pi <-- Pi allows one to establish a direct connection between the vibration-rotation angular momentum coupling and the resulting spectra. Due to the l-doubling, the Q-branch is split into two subbranches characterized by either even or odd rotational quantum number j. The vibrational bending reduces the rotational transfer rates inside each of these subbranches by a factor of about two and induces an inter-subbranch coupling. The expected propensity rule towards conservation of the parity index for high rotational levels is well observed. Calculated spectra are in excellent agreement with CARS experiments for the nu(1) + nu(2)<--nu(2) band of CO2. (C) 1997 Elsevier Science Ltd.