This paper reports the simultaneous internal state and translational energy resolved associative desorption flux of N 2 from Ru͑0001͒ using two different experimental approaches. Both experiments show that the nascent N 2 is formed with little vibrational excitation and that the total excitation in all N 2 degrees of freedom accounts for only 1 3 of the barrier energy. Roughly 2 3 of the energy necessary to surmount the barrier is lost to the surface in desorption. This behavior, as well as the unusual behavior noted previously in direct measurements of dissociative adsorption, both imply strong vibrational quenching in reactive trajectories passing over the high exit channel ͑vibrational͒ barrier. Adiabatic quasiclassical dynamical calculations based on the ab initio potential energy surface and various models of coupling to the lattice are not qualitatively consistent with N 2 vibrational damping to phonons. However, including a strong nonadiabatic coupling of the vibrational coordinate to electron-hole pairs in the dynamics does yield qualitative agreement between experiments and calculated dynamics, and we suggest this as indirect evidence for strong nonadiabatic coupling. We argue that the nonadiabatic coupling is strong in this case because of the high vibrational excitation necessary to pass over the high exit channel barrier in the reactive processes and the large charge transfer inherent in making or breaking bonds. We believe that the same factors will be important in most activated dissociations of bonded molecules on transition metal surfaces, e.g., for O 2 , NO, N 2 , and CO, and if this scenario is correct then nonadiabaticity should be important in the activated dissociation dynamics of these systems as well.

New molecular beam experiments on the dissociation probability S 0 for N 2 on Ru͑0001͒ are presented. These are in general agreement with prior measurements and exhibit very unusual behavior; a very slow increase of S 0 with incident kinetic energy E and the fact that S 0 is still only ϳ10 Ϫ3 at incident energies considerably above the barrier. A simple dynamical model is developed to describe this unusual sticking behavior. The key aspect is that there is considerable energy loss ⌬ from E upon initial impact with the surface ͑principally to the lattice͒ and only EϪ⌬ is then available to surmount the activation barrier in the exit channel. Using experimentally measured values of ⌬ from scattering experiments gives good qualitative agreement of this model with the measured S 0. One implication of the strong energy loss is that there is an apparent violation of detailed balance when comparing only the reactive fluxes of activated adsorption and associative desorption.

A large number of curling shots using a wide range of rotational and translational velocities on two different ice surfaces have been recorded and analyzed. The observed curling-rock trajectories are described in terms of a semi-phenomenological model. The data are found to rule out "dry-friction" models for the observed motion, and to support the idea that the curling rock rides upon a thin liquid film created at the ice surface (i.e., "wet friction"). Evidence is found to support the hypothesis that the frictional force acting upon each segment of the curling rock is directed opposite to the motion relative to this thin liquid film and not relative to the underlying fixed ice surface. PACS No.: 01.80.+b

We report the polarized emission spectra from photodissociating nitromethane excited at 200 and 218 nm. At both excitation wavelengths, the emission spectra show a strong progression in the NO2 symmetric stretch; at 200 nm a weak progression in the NO2 symmetric stretch in combination with one quantum in the C–N stretch also contributes to the spectra. We measure the angular distribution of emitted photons in the strong emission features from the relative intensity ratio between photons detected perpendicular to versus along the direction of the electric vector of the excitation laser. We find the anisotropy is substantially reduced from the 2:1 ratio expected for the pure CH3NO2 X(1A1)→1B2(ππ*)→X(1A1) transition with no rotation of the molecular frame. The intensity ratios for the features in the NO2 symmetric stretching progression lie near 1.5 to 1.6 for 200 nm excitation and 1.7 for 218 nm excitation. The analysis of the photon angular distribution measurements and consideration of the absorption spectrum indicate that the timescale of the dissociation is too fast for molecular rotation to contribute significantly to the observed reduction in anisotropy. The detailed analysis of our results in conjunction with electron correlation arguments and previous work on the absorption spectroscopy and final products’ velocities results in a model which includes two dissociation pathways for nitromethane, an electronic predissociation pathway and a vibrational predissociation pathway along the 1B2(ππ*) surface. Our analysis suggests a reassignment of the minor dissociation channel, first evidenced in photofragment velocity analysis experiments which detected a pathway producing slow CH3 fragments, to the near threshold dissociation channel CH3 + NO2(2 2B2).

Detailed measurements of state resolved inelastic scattering of N2 from Ru(0001) are reported for a wide range of initial energies (0–3 eV) and angles of incidence. The ion time-of-flight resonantly enhanced multiphoton ionization (REMPI) detection scheme developed here and used with cw molecular beams simultaneously measures the internal quantum state and translational energy normal to the sample surface. Doppler broadening of the REMPI spectrum of scattered particles yields the dispersion in scattering out of plane. The results are qualitatively similar to inelastic N2 scattering studies for a wide variety of other metal surfaces; i.e., no observable vibrational excitation, weak rotational excitation described as a Boltzmann distribution, strong surface excitation depending upon the incident normal energy, and an anticorrelation between rotational and surface excitation. The absence of any vibrational excitation at E≈3 eV is inconsistent with adiabatic model dynamics based on the ab initio potential-energy surface. It is, however, consistent with a strong nonadiabatic damping of vibration to electron-hole pairs in the region of the barrier. This same suggestion was previously found necessary to rationalize unusual dissociative adsorption and associative desorption of N2 on Ru(0001).