COLLISION-INDUCED DOUBLE TRANSITION EFFECTS IN THE 3-NU(3) CO2 BAND WING REGION

IR absorption beyond the head of the 00(0)3-00(0)0 (3 nu(3)) band of C O2 near 7000 cm(-1) has been analyzed. This absorption is found to con sist of two comparable intensity contributions, namely, the allowed ba nd wing and a collision-induced absorption (CIA) band. The band wing p rofile has been described by using a non-Markovian theory and the rota tional perturbation densities for CO2-CO2 collisions, which was previo usly calculated from the intensity distribution in the high-frequency wing of the 00(0)1-00(0)0 CO2 band. The CIA component has a typical sh ape of CO2 CIA bands with the maximum at the double transition (00(0)1 +00(0)2)-(00(0)0+00(0)0) frequency. The integrated binary coefficient of this CIA band was estimated to be B-2=(1.0+/-0.6)x10(-5) cm(-2) Ama gat(-2). The CIA spectral moment theory has been used for the intensit y calculation, which takes into account for the first time the collisi on-induced vibrational force field in CO2 pairs. By comparing the calc ulated and measured intensity for the double transition, the polarizab ility anisotropy matrix element for the 2 nu(3) band has been estimate d as beta(20)=0.26+/-0.08 a.u., value in reasonable agreement with an independent estimation from previous results of polarizability matrix elements of CO2. (C) 1997 American Institute of Physics.