Articles you may be interested inQuantum dynamical treatment of inelastic scattering of atoms at a surface at finite temperature: The random phase thermal wave function approach Erratum: "Comparative dynamics of Cl ( 2 P) and O ( 3 P) interactions with a hydrocarbon surface" [J. Chem. Eley-Rideal reactions between H atoms on metal and graphite surfaces: The variation of reactivity with substrateThe dynamics of the initial interactions of hyperthermal O atoms with a saturated hydrocarbon surface have been investigated by directing an O-atom beam at a continuously refreshed liquid squalane surface and monitoring time-of-flight and angular distributions of inelastically scattered O atoms and reactively scattered OH and H 2 O. These products are formed through thermal and nonthermal processes. The inelastic scattering processes may be described in terms of the limiting cases of direct inelastic scattering ͑nonthermal͒ and trapping desorption ͑thermal͒. The initial step leading to production of volatile OH and H 2 O is believed to be direct H-atom abstraction to form OH. Once formed, the OH may scatter directly into the gas phase before thermal equilibrium with the surface is reached, or it may undergo further collisions and reactions with the surface. These secondary interactions include trapping and desorption of OH and abstraction of a second hydrogen atom to form H 2 O. Interactions that occur before thermal equilibrium with the surface can be reached lead to products that exit the surface at hyperthermal velocities, while those that occur in thermal equilibrium with the surface yield products that leave the surface at thermal velocities given by the surface temperature. Direct, single-collision scattering events that produce O and OH are described with a kinematic picture that allows the determination of the effective surface mass encountered by an incident O atom, the atom-surface collision energy in the center-of-mass frame, and the fraction of the center-of-mass collision energy that goes into translation of the scattered gaseous product and the recoiling surface fragment. Center-of-mass velocity-flux maps for OH indicate either single-collision events through a largely collinear O-H-C transition state or multiple-collision events in which initially formed OH scatters inelastically from the surface.

This paper presents a combined experimental and theoretical study of the dynamics of O((3)P) + D(2) collisions, with emphasis on a center-of-mass (c.m.) collision energy of 25 kcal mol(-1). The experiments were conducted with a crossed-molecular-beams apparatus, employing a laser detonation source to produce hyperthermal atomic oxygen and mass spectrometric detection to measure the product angular and time-of-flight distributions. The novel beam source, which enabled these experiments to be conducted, contributed unique challenges to the experiments and to the analysis, so the experimental methods and approach to the analysis are discussed in detail. Three different levels of theory were used: (1) quasiclassical trajectories (QCT), (2) time-independent quantum scattering calculations based on high-quality potential surfaces for the two lower-energy triplet states, and (3) trajectory-surface-hopping (TSH) studies that couple the triplet surfaces with the lowest singlet surface using a spin-orbit Hamiltonian derived from ab-initio calculations. The latter calculations explore the importance of intersystem crossing in the dynamics. Both experiment and theory show that inelastically scattered O atoms scatter almost exclusively in the forward direction, with little or no loss of translational energy. For the reaction, O((3)P) + D(2) --> OD + D, the experiment shows that, on average, approximately 50% of the available energy goes into product translation and that the OD product angular distributions are largely backward-peaked. These results may be interpreted in light of the QCT and TSH calculations, leading to the conclusion that the reaction occurs mainly on triplet potential energy surfaces with, at most, minor intersystem crossing to a singlet surface. Reaction on either of the two low-lying reactive triplet surfaces proceeds through a rebound mechanism in which the angular distributions are backward-peaked and the product OD is both vibrationally and rotationally excited. The quantum scattering results are in good agreement with QCT calculations, indicating that quantum effects are relatively small for this reaction at a collision energy of 25 kcal mol(-1).

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We present the first measurements of the relative excitation function for the O(3P)+H2 reaction, performed with the use of a crossed molecular beams apparatus in conjunction with a high-energy (laser detonation) source of O atoms. The results are in excellent agreement with accurate quantum wave packet calculations.

The excitation function for the reaction, O(3P)+CH4-->H+OCH3, has been measured in a crossed molecular beams experiment and determined with direct dynamics calculations that use the quasiclassical trajectory method in conjunction with a recently developed semiempirical Hamiltonian. Good agreement is found between experiment and theory, enabling us to address two fundamental issues for the O(3P)+CH4 reaction that arise for all O(3P)+saturated hydrocarbon reactions: (1) the importance of triplet excited states that correlate adiabatically to ground-state reactants and products and (2) the importance of intersystem crossing processes involving the lowest singlet surface [corresponding to reaction with O(1D)]. Our results indicate that the first excited triplet surface contributes substantially to the cross section when the collision energy exceeds the reaction barrier (approximately 2 eV) by more than 0.5 eV. Although triplet-singlet crossings may occur at all energies, we have found that their effect on the excitation function is negligible for the collision energies studied-up to 1.5 eV above threshold.