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 ultraviolet pumping is measured on a picosecond time scale. Fourier transform infrared measurements establish that v(1) is anharmonically coupled to the frustrated translation near 32 cm(-1) (v(4)), so that transient shifts in v(1) indicate population changes in V-4. The v(1) response to visible and ultraviolet pumping is characterized by a spectral shift near zero delay time, which decays with a approximate to 2 ps time constant to an intermediate value, which then decays on a approximate to 200 ps time scale. The data agree well with a model whereby v(4) couples 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.