Direct vibrational excitation in gas-surface collisions of NO with Ag(111)

Thermal accommodation coefficients between polyatomic gas molecules and soot in laser-induced incandescence experiments

“…In gas/surface scattering the vibrational energy modes of gas molecules are most often accessed through one of two mechanisms [29][30][31]: gas molecules having a large incident velocity (which is often the case in molecular beam experiments) can have some of their translational kinetic energy redistributed to internal modes through the collision; and alternatively, gas molecules with lower incident energy can follow a trapping/desorption channel, which allows time for the gas molecules to equilibrate with the surface. Neither scenario applies in this system, however, since incident gas molecules effusing from a gas at 300 K have low incident translational energy (and very few of them are vibrationally excited), while the high surface temperature relative to the potential well prevents the gas molecules from becoming adsorbed onto the surface.…”

Observation of a Change of Vibrational Excitation Mechanism with Surface Temperature: HCl Collisions with Au(111)

“…Both experiment and theory have probed many aspects of such interactions including translational, vibrational, and rotational energy transfer between gasphase molecules and surface atoms [1][2][3][4][5][6]. Since the flow of energy into and out of chemical bonds is essential to bond rupture and formation, vibrational energy transfer takes a prominent place in this field [7][8][9][10][11][12]. For example, vibrationally inelastic scattering can be a sensitive probe of portions of the potential surface near the dissociation barrier [13].…”

“…In addition, the near harmonic nature of phonon motion and the low probability to couple multiple phonons to molecular vibration leads to a weak or absent dependence on T s [12]. Electronically nonadiabatic mechanisms for vibrational excitation, in contrast, may exhibit little or no incidence energy threshold as well as a characteristic pseudo-Arrhenius T s dependence resulting from the strong T s -dependent variation of the Fermi function [11,17]. More recent evidence for the efficient coupling of intramolecular vibrational motion to EHP excitations comes from the study of interactions of highly vibrationally excited molecules with metal surfaces.…”

“…In comparison to NO (v 0 ! 1) on Ag(111) where the largest excitation probability for NO is as high as 0:07 [11,17], it is clear that the energy transfer is much less efficient for HCl=Au compared to NO=Ag. Second, the vibrational excitation probabilities of HCl (v 0 !…”

Testing the limits of the Maxwell distribution of velocities for atoms flying nearly parallel to the walls of a thin cell

“…For most molecular gases, the temperature of the surface (or of the whole cell body) can be changed without affecting the molecular gas density or pressure, so that simple processes can be sufficient to build-up the thin gas cell. A study of this influence of the surface temperature, with respect to the slow atoms of a given rovibrational level would be of interest, noting that it is frequent that molecule-surface interaction does not equally "thermalize" rotation, vibration, and translation [5,50,51] A general difficulty with the principle of our set-up may be found in the competition between the observation of atoms with a very infrequent trajectory, and the possibility that atom-atom collisions, occurring somewhere in the "middle" of the cell, release atoms with "parallel" trajectories, which keep memory of their pumping in spite of having collided the walls after the pumping step. The background of velocity changing collisions in our experiments, discriminated from the main signal by its shape, is an indication that these gas collisions may restrict the applicability of our technique.…”