An advanced molecule-surface scattering instrument for study of vibrational energy transfer in gas-solid collisions (original) (raw)
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Effect of the molecular structure on the gas-surface scattering studied by supersonic molecular beam
The European Physical Journal D, 2006
The experimental apparatus for investigating the gas-surface interaction has been newly developed. The coherent length of the helium, the energy resolution and the angular spread of the beam in the apparatus were established as ω = 16 nm, ∆E/E = 2.4% and ∆θ = 0.5 • , respectively, through the measurements of the time-of-flight of He beam and of the angular intensity distributions of He scattered from LiF(001). The angular intensity distributions of Ar, N2 and CO scattered from the LiF surface along the [100] azimuthal direction were then measured as a function of incident translational energy. The effects of the molecular structural anisotropy and center-of-mass position on the gas-surface inelastic collision at the corrugated surface are discussed with predictions based on a recently developed simple classical theory of the ellipsoid-washboard model. PACS. 68.49.Bc Atom scattering from surfaces (diffraction and energy transfer) -68.49.Df Molecule scattering from surfaces (energy transfer, resonances, trapping) -34.50.Dy Interactions of atoms and molecules with surfaces; photon and electron emission; neutralization of ions -68.49.-h Surface characterization by particle-surface scattering 130 The European Physical Journal D
Physica Scripta, 2006
Production, characterization and control of alignment degree of molecules are of importance for investigating in detail the stereodynamics of elementary processes involving elastic, inelastic and reactive events and also to prepare gas-phase species for selective surface scattering investigations. The focus here is on collisional alignment in supersonic seeded molecular beams, a technique which shows perspectives on the applications, offering appealing features for 'duty cycle' and intensity characteristics. Attention will be addressed to recent stereodynamical studies carried out on hydrocarbon molecules in the gas phase and on applications of such aligned beams to surface scattering studies.
Quantum-state specific scattering of molecules from surfaces
2014
In my work, I investigated the quantum-state resolved scattering of three different diatomic molecules (NO, CO, N 2 ) from different surfaces, including Au(111) and Pt(111). I focused on measurements of the energy transfer between the various degrees of freedom available using both state-of-the-art and new methods developed in the course of this work. I strove to investigate a few simple model systems with the goal of discovering generally valid rules for the coupling between different degrees of freedom of these simple model systems. As a first system, I investigated vibrationally inelastic scattering of nitric oxide (NO) from a single crystal Au(111) surface, a system that has been extensively studied in the past and is thought to be well understood. I measured absolute vibrational excitation probabilities for v = 0→1, 2, 3 scattering as a function of surface temperature and incidence translational energy and compared the results to first-principles independent electron surface-ho...
Vibrational energy in molecules probed with high time and space resolution
International Reviews in Physical Chemistry, 2007
This article reviews experimental measurements of vibrational energy in condensed-phase molecules that simultaneously provide time resolution of picoseconds and spatial resolution of a˚ngstro¨ms. In these measurements, ultrashort light pulses are used to input vibrational energy and probe dynamical processes. High spatial resolution is obtained using vibrational reporter groups in known locations on the molecules. Three examples are discussed in detail:
Review of Scientific Instruments, 2011
An effusive molecular beam technique is described to measure alkane dissociative sticking coefficients, S(Tg, Ts; ϑ), on metal surfaces for which the impinging gas temperature, Tg, and surface temperature, Ts, can be independently varied, along with the angle of incidence, ϑ, of the impinging gas. Effusive beam experiments with Tg = Ts = T allow for determination of angle-resolved dissociative sticking coefficients, S(T; ϑ), which when averaged over the cos (ϑ)/π angular distribution appropriate to the impinging flux from a thermal ambient gas yield the thermal dissociative sticking coefficient, S(T). Nonequilibrium S(Tg, Ts; ϑ) measurements for which Tg ≠ Ts provide additional opportunities to characterize the transition state and gas–surface energy transfer at reactive energies. A resistively heated effusive molecular beam doser controls the Tg of the impinging gas striking the surface. The flux of molecules striking the surface from the effusive beam is determined from knowledge ...
Phys. Chem. Chem. Phys., 2011
Here we extend a recently introduced state-to-state kinetic model describing single-and multi-quantum vibrational excitation of molecular beams of NO scattering from a Au(111) metal surface. We derive an analytical expression for the rate of electronically non-adiabatic vibrational energy transfer, which is then employed in the analysis of the temperature dependence of the kinetics of direct overtone and two-step sequential energy transfer mechanisms. We show that the Arrhenius surface temperature dependence for vibrational excitation probability reported in many previous studies emerges as a low temperature limit of a more general solution that describes the approach to thermal equilibrium in the limit of infinite interaction time and that the pre-exponential term of the Arrhenius expression can be used not only to distinguish between the direct overtone and sequential mechanisms, but also to deduce their relative contributions. We also apply the analytical expression for the vibrational energy transfer rates introduced in this work to the full kinetic model and obtain an excellent fit to experimental data, the results of which show how to extract numerical values of the molecule-surface coupling strength and its fundamental properties.
Possible quantum effects in collisional energy transfer in highly excited molecules
Chemical Physics Letters, 1990
It has been observed that classical trajectory calculations of energy transfer rates in large highly excited molecules with He bath gas give values much higher than experiment. This might be caused by quantum effects in which contributions from higher partial waves do not contribute to energy transfer. Experimental means of testing this postulate are proposed.
Physical Review Letters, 2001
This work represents the first experimental demonstration that planar molecules tend to travel as a "frisbee" when a gaseous mixture with lighter carriers expands into a vacuum, the orientation being due to collisions. The molecule is benzene, the prototype of aromatic chemistry. The demonstration is via two complementary experiments: interrogating benzene by IR-laser light and controlling its orientation by selective scattering on rare gas targets. The results cast new light on the microscopic mechanisms of collisional alignment and suggest a useful way to produce intense beams of aligned molecules, permitting studies of steric effects in gas-phase processes and in surface catalysis.