15min:
SPECTROSCOPY OF ACETYLENE TRIPLET STATES BY DIRECT OPTICAL EXCITATION.

R. L. THOM AND R. W. FIELD, Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139.

We present here initial results of the first experiments detecting direct optical (uv) excitation of spin-forbidden transitions from the singlet ground electronic surface ( S 0) of acetylene into the low-lying molecular triplet manifold ( T 1, T 2). The metastable states thus populated are detected via electron ejection from a Cs metal surface (SEELEM: Surface Electron Ejection by Laser Excited Metastables spectroscopy). Initial insights into the structural and dynamical properties of these states, and the mechanism of the SEELEM detection process, are discussed.