ELECTRON-IMPACT DESORPTION OF METASTABLE PARTICLES FROM CO FILMS

The impact of monochromatic low-energy electrons (4-52 eV) is found to induce desorption of metastable particles (MP) from multilayer films formed by condensing CO gas on a Pt(111) substrate held at 20 K. The r esults are compared with metastable production from gaseous CO. Metast able CO (CO) is identified as the major desorbed species, its desorpt ion is discussed in terms of intramolecular to molecule-surface vibrat ional energy transfer. Primary electronic excitation proceeds via the states, a '(3)Sigma(+), d(3)Delta, e(3)Sigma(-), I(1)Sigma(-), and D(1 )Delta which contribute to MP desorption directly or by first decaying in high vibrational levels of the a(3)Pi configuration. The energy th reshold of 8.0 eV for CO desorption indicates that CO in low vibratio nal levels of the a(3)Pi state does not desorb. Electronic excitation occurs either near the surface of the CO film or in the bulk. In the l atter case, excitonic motion to the surface can be followed by CO des orption. (C) 1998 American Institute of Physics. [S1063-777X(98)00910- 4]