Multiple resonance-enhanced four-wave-mixing processes in I2

Resonance-enhanced four-wave-mixing processes were studied in molecular iodine by detection of a wave generated at frequency 3=21-2 for a wide range of Raman frequencies (1-2). On the basis of known spectroscopic constants of the two electronic states involved, the electronic ground state X 1g+ and the electronic excited state B 3 u0+, an interpretation of the spectral features in terms of three essentially different four-wave-mixing processes is given. Resonance enhancement through bound states with discrete energy levels and the enhancement effect by dissociative continuum states are considered. In addition to resonance-enhanced coherent anti-Stokes Raman-scattering (CARS) processes, in which the Raman resonances are in the electronic ground state, two resonant schemes are identified in I2, in which Raman resonances in an excited state are probed: excited-state parametric and nonparametric CARS. The latter process is an example of electronic population transfer in a four-wave-mixing cycle.