RESONANCES IN THE PHOTODISSOCIATION OF CO2 - PERIODIC-ORBIT AND WAVEPACKET ANALYSES

The photodissociation of CO2 on the LEPS model potential surface [K.C. Kulander, J.C. Light, J. Chem, Phys. 73 (1980) 4337] is investigated in view of identifying the ultrashort-lived resonances that characteri ze the 'diffuse' structures in the absorption cross section. To this e nd, two avenues are pursued: on the one hand, regular and chaotic regi mes are identified in the classical phase space, and semiclassical qua ntization is carried out for both regimes, In particular, the regular regime is amenable to a perturbative treatment which yields three low- energy resonances of symmetric-stretch character, with the associated bending progressions. The chaotic regime is analyzed by periodic-orbit quantization, within the collinear model. We identify partially inter leaved progressions of resonances, of both even and odd parity. Period ic orbits of 'off-diagonal' type are found to play the dominant role i n generating these progressions, The second avenue to identifying the resonance structures is a quantum-mechanical analysis, Different initi al conditions, again of even and odd parity, are used in wavepacket pr opagation to probe different spectral regions. The resonances are extr acted from the spectra obtained by Fourier-transforming the wavepacket autocorrelation function. The agreement between the complementary sem iclassical and quantum analyses is found to be very satisfactory. The resonance lifetimes determined in our analysis range from 4 to 60 fs. (C) 1997 Elsevier Science B.V.