Half-collision studies of singlet-to-triplet energy transfer: action spectroscopy and predissociation dynamics of electronically excited Cd H2 and Cd D2 complexes

The Cd·H2 and Cd·D2 van der Waals complexes have been synthesized by expanding cadmium vapor and He/H2 mixtures into a supersonic free jet. The `half-collision' process, Cd(5s5p 1P1)·H2 → Cd(5s5p 3P J) + H2, was studied by fixing a probe dye laser pulse (delayed 10 ns) onto one of the Cd(5s6s 3S1 ← 5s5p 3PJ) transitions while exciting the Cd·H2(Cd·D2) complex with a pump dye laser pulse tuned across frequencies near that of the free Cd(5s5p 1P1 ← 5s5s 1S0) atomic transition. When the probe laser was tuned to detect Cd(5s5p 3P2), an action spectrum to the red of the atomic transition was obtained for Cd·H2, consisting of a broad continuum superimposed upon which was an anharmonic series of vibrational transitions with discernible, blue-shaded rotational structure. A similar spectrum was recorded for Cd·D2, except that only very broadened blue-shaded rotational structure was observed.