Subband analysis of molecular electronic transitions by nonlinear polarization spectroscopy in the frequency domain

Nonlinear polarization spectroscopy in the frequency domain (NLPF) allows a detailed analysis of substructure behind a molecular optical absorption band. Using the chi((3))-approach here we deduce theoretically line shapes of NLPF spectra for systems with more than one optical transition, which contribute to linear as well as excited state absorption. It is possible from such line shapes to decide whether these transitions are independent from each other or belong to a common ground state. We demonstrate further how energy transfer and relaxation paths can be revealed and quantified by a global analysis of NLPF spectra. This is useful to get a comprehensive understanding of ultrafast processes in complex molecular and supermolecular systems. (C) 1998 American Institute of Physics. [S0021-9606(98)00647-3].