The fluorescence depletion spectroscopy of CdCH3

The fluorescence depletion spectroscopy (FDS) technique has been applied to the (A) over tilde(2)E electronic state of the CdCH3 radical to investigat e "dark'' vibronic levels. The observed FDS spectrum complements the sparse laser- induced fluorescence and resonance-enhanced multiphoton ionization spectra. Both the upper and lower spin components of the vibrationless leve l as well as excitations involving the symmetric modes nu(2) and nu(3), and the antisymmetric mode nu(6), as well as combinations involving these mode s, were observed. A combined Jahn-Teller and spin-orbit coupling model was used to explain the vibronic structure in the (A) over tilde(2)E electronic state as well as strong variations in the Coriolis coupling constants obta ined from the resolved rotational K structure. Lifetimes for fluorescing le vels have been determined from their temporal decay and those for some dark levels via lifetime broadening measurements. The selectivity of the radiat ionless decay channel and its possible attribution to an isomerization proc ess are discussed. (C) 1999 American Institute of Physics. [S0021-9606(99)0 1204-0].