QUANTUM-RESOLVED ANGULAR-DISTRIBUTIONS OF NEUTRAL PRODUCTS IN ELECTRON-STIMULATED PROCESSES - DESORPTION OF CO-ASTERISK FROM PT(111)

The first quantum-resolved angular distribution measurements of electronically excited neutral molecules which have undergone electron stimulated desorption (ESD) are presented. Two-dimensional imaging of laser resonance-enhanced multiphoton ionization (REMPI) is used to obtain angular distributions of CO* in the nu = 0 vibrational level of the metastable a3PI(r), state desorbed from CO/Pt(111) by 350 eV electrons. For saturation CO coverages at 90 K, sharp Gaussian distributions peaked about the surface normal (6-degrees +/- 0.5-degrees half-width at half maximum) are observed, consistent with previously reported data acquired by ESDIAD (ESD ion angular distributions). The (1 + 1) photon REMPI scheme for state-specific CO* detection involves the b3SIGMA(nu = 0) <-- a3PI(nu = 0) transition at 283 nm, followed by photoionization al the same wavelength. In this paper, the overall experimental technique for REMPI imaging of products from electron stimulated processes is discussed. Thus specific CO* data as a function of coverage and temperature is presented for comparison with the ESDIAD results.