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].