Ultrafast laser pulses on Ir{111} cause a highly temperature-dependent redshift of the intramolecular stretch frequency of adsorbed NO. The time-resolved spectral changes are driven by charge transfer of hot electrons to the NO 2pi*d antibonding orbital, which leads to bending of NO and internal bond weakening. The nonadiabatic change in the NO adsorption geometry follows the charge transfer within a time scale of 700 femtoseconds. This geometrical change is the same as the mechanism predicted for thermally induced dissociation.

We present a set of experiments that provide a complete mapping of coherent and incoherent vibrational relaxation times for a molecule on a metal surface, CO/Ir{111}. Included is the first detection of a midinfrared photon echo from a metallic surface, some 15 years after the analogous measurement on a semiconductor surface, which sets a precedent for the ability to manipulate and rephase polarization on a subpicosecond time scale on surfaces. For the C-O stretch in a strongly dipole-coupled CO layer we obtain a total linewidth of 5.6 cm-1, composed of a homogeneous width of 2.7 cm-1 and an inhomogeneous contribution of 3.0 cm-1. Pure dephasing is negligible at liquid nitrogen temperatures, making CO/Ir{111} an attractive model system for quantum computing.

Hot electrons created by femtosecond laser pulses can transiently increase the occupation of the antibonding 2π* orbital of a diatomic adsorbate and change its bonding configuration. By monitoring the intramolecular stretch frequency of CO and NO on Ir{111} with time-resolved sum frequency spectroscopy, we demonstrate how the vibrational dynamics depend on the degree of charge flow between the surface and the adsorbate. We find CO and NO to be model adsorbates for adiabatic and nonadiabatic dynamics, respectively.