The femtosecond laser desorption yield of molecular CO from Cu(111) is measured with 800 and 400 nm wavelength radiation and compared to previous studies using 620 nm radiation(J. A. Prybyla, H. W. K. Tom and G. D. Aumiller, Phys. Rev. Lett. \textbf68), 503(1992). The desorption yield is less nonlinear with absorbed fluence and more efficient for shorter wavelength radiation. Surprisingly, for 400 nm (3 eV) radiation 100% of the CO molecules may be desorbed. This observation indicates the
importance of the copper d-band states in femtosecond laser- induced
desorption. First, the d-bands provide the initial states for photoexcited
electronic populations at \sim 1 and 4 eV above E_F. Secondly, the d-band
holes become a secondary source of hot electrons through Auger recombination
and other scattering processes. The density of 3-4 eV electrons can thus
be high and have a surface residence time of 20-30 fs(S. Ogawa, H. Nagano
and T. Petek, Phys. Rev. B \textbf55), 10869(1997). Both are necessary
components to proposed desorption mechanisms involving multiple electronic
excitation-deexcitation cycles on a timescale short compared to the molecule-substrate
stretch mode period.