PICOSECOND TIME-RESOLVED ADSORBATE RESPONSE TO SUBSTRATE HEATING - SPECTROSCOPY AND DYNAMICS OF CO CU(100)/

The response of the molecular stretch mode of CO/Cu(100) near 2086 cm( -1) (v(1)) to resonant infrared, and nonresonant visible and ultraviol et pumping is measured on a picosecond time scale. Fourier transform i nfrared measurements establish that v(1) is anharmonically coupled to the frustrated translation near 32 cm(-1) (v(4)), so that transient sh ifts in v(1) indicate population changes in V-4. The v(1) response to visible and ultraviolet pumping is characterized by a spectral shift n ear zero delay time, which decays with a approximate to 2 ps time cons tant to an intermediate value, which then decays on a approximate to 2 00 ps time scale. The data agree well with a model whereby v(4) couple s to both the photogenerated hot electrons and to the heated phonons. The characteristic coupling times to these two heat baths are found to both be a few picoseconds.