Laser-Surface-Adsorbate Interactions: Thermal versus Photoelectronic Excitation of Mo(co)6on Si(111)

Laser-induced electronic excitation of adsorbed Mo${\mathrm{}\left(\mathrm{CO}\right)\mathrm{}}_6$ followed by CO desorption is observed to occur on Si(111) (7 × 7) irradiated with 257-nm (4.8 eV) laser radiation. The process is shown to be completely nonthermal in nature. In contrast, irradiation with 514-nm radiation is found to be identical to resistive heating of the crystal. Adsorption does not open up new excitation mechanisms that allow decomposition to occur in the visible region of the spectrum.