Angle resolved intensity and velocity distributions of N2 desorbed by N2O decomposition on Rh(110).

The angle resolved intensity and velocity distributions of desorbing product N(2) were measured under a steady-state N(2)O+CO reaction on Rh(110) by cross-correlation time-of-flight techniques. Three-dimensional intensity distribution of N(2) has been constructed from the angle resolved intensity distributions in the planes along different crystal azimuths. N(2) desorption has been found to split into two lobes sharply collimated along 50-63 degrees off normal toward [001] and [001] directions, suggesting that N(2)O is decomposed through the transition state of N(2)O adsorbed with the molecular axis parallel to the [001] direction.

Polar- and azimuth-angle-dependent rotational and vibrational excitation of desorbing product CO2 in CO oxidation on palladium surfaces.

Clear polar and azimuth angle dependencies were found in rotational and vibrational energies of product CO2 in CO oxidation on Pd surfaces. On Pd(110)-(1x1), with increases in polar angle, both energies decreased in the [001] direction but remained constant in [110]. On the Pd(110) with missing rows, both energies increased in [001] but decreased in [110], indicating that the transition state changes with the geometry of the substrate.

N2 emission in NO and N2O reduction on Rh(100) and Rh(110).

The angular distribution of desorbing N(2) was studied in both the thermal decomposition of N(2)O(a) on Rh(100) at 60-140 K and the steady-state NO (or N(2)O) + D(2) reaction on Rh(100) and Rh(110) at 280-900 K. In the former, N(2) desorption shows two peaks at around 85 and 110 K. At low N(2)O coverage, the desorption at 85 K collimates at about 66 degrees off normal towards the [001] direction, whereas at high coverage, it sharply collimates along the surface normal.

Internal-energy measurements of angle-resolved product CO2 in catalytic CO oxidation by means of infrared chemiluminescence.

Measurements of both vibrational and rotational energies of product CO(2) in CO oxidation on palladium surfaces have been successfully performed as a function of the desorption angle by means of infrared chemiluminescence. The remarkable angle dependences of both energies indicate facile energy partitioning in repulsive desorption and provide new dimensions in the study of surface reaction dynamics as well as additional insights into the product formation site. Details of the apparatus for energy analysis of angle-resolved products are described, especially on how to pick up extremely weak infrared emission signals.

Interplay of first-order kinetic and thermodynamic phase transitions in heterogeneous catalytic reactions.

Using the rate constants obtained on the basis of independent transient measurements and density functional theory calculations, we perform Monte Carlo (MC) simulations of the bistable kinetics of the N2O-CO reaction on Pd(110) at 450 K. In the absence of lateral interactions, the MC technique predicts a wide hysteresis loop in perfect agreement with the mean-field analysis. With attractive substrate-mediated lateral interactions resulting in the formation of (1 x 2) O islands and reducing the reaction rate inside islands, the hysteresis is found to be dramatically (about 5 times) narrower.

The collimation angle shift of desorbing product N2 in a steady-state N2O+CO reaction on Rh(110).

The angular distribution of desorbing product N2 was studied in N2O decompositions on Rh(110) in the temperature range of 60-700 K. The N2 desorption collimates along 62 degrees -68 degrees off normal toward either the [001] or [001] direction in a transient N2O decomposition below ca. 470 K or in the steady-state N2O+CO reaction above 540 K.

Inclined N2 desorption in a steady-state N2O + CO reaction on Pd(110).

The angular and velocity distributions of desorbing products were analyzed in the course of a catalyzed N2O + CO reaction on Pd(110). The reaction proceeded steadily above 450 K, and the N2 desorption merely collimated sharply along 45 degrees off the surface normal toward the [001] direction. It is proposed that this peculiar N2 desorption is induced by the decomposition of adsorbed N2O oriented along the [001] direction.

Inclined N2 desorption in a steady-state NO + CO reaction on Pt(100).

The angular and velocity distributions of desorbing products N2 and CO2 were studied in a steady-state NO + CO reaction on Pt(100). From the observation of the inclined N2 desorption, a contribution of the intermediate N2O decomposition pathway was first proposed on this surface. On the other hand, CO2 desorption collimated along the surface normal.

Surface-nitrogen removal in a steady-state NO + H2 reaction on Pd(110).

Surface-nitrogen removal steps were analyzed in the course of a catalyzed NO + H(2) reaction on Pd(110) by angle-resolved mass spectroscopy combined with cross-correlation time-of-flight techniques. Four removal steps, i.e.

Spatial distributions of desorbing products in steady-state NO and N2O reductions on Pd(110).

The angular and velocity distributions of desorbing product N(2) were examined over the crystal azimuth in steady-state NO+CO and N(2)O+CO reactions on Pd(110) by cross-correlation time-of-flight techniques. At surface temperatures below 600 K, N(2) desorption in both reactions splits into two directional lobes collimated along 41 degrees -45 degrees from the surface normal toward the [001] and [001] directions. Above 600 K, the normally directed N(2) desorption is enhanced in the NO reduction.

Inclined N2 desorption in N2O reduction by D2 and CO on Pd(110).

Inclined N2 desorption was examined in the course of a catalyzed N2O + D2 (or CO) reaction on Pd(110) by angle-resolved mass spectroscopy combined with cross-correlation time-of-flight techniques. N2 desorption collimated at around 45 degrees off the normal toward the [001] direction in the temperature range of 400-800 K. Its collimation angle and kinetic energy were insensitive to both the surface temperature and surface conditions throughout the kinetic transition.

Kinetics and dynamics of N2 formation in a steady-state N2O + CO reaction on Pd(110).

The N(2)O decomposition kinetics and the product (N(2) and CO(2)) desorption dynamics were studied in the course of a catalyzed N(2)O+CO reaction on Pd(110) by angle-resolved mass spectroscopy combined with cross-correlation time-of-flight techniques. The reaction proceeded steadily above 400 K, and the kinetics was switched at a critical CO/N(2)O pressure ratio. The ratio was about 0.

Collision-induced desorption in 193-nm photoinduced reactions in (O2+CO) adlayers on Pt(112).

The spatial distribution of desorbing O(2) and CO(2) was examined in 193-nm photoinduced reactions in O(2)+CO adlayers on stepped Pt (112)=[(s)3(111)x(001)]. The O(2) desorption collimated in inclined ways in the plane along the surface trough, confirming the hot-atom collision mechanism. In the presence of CO(a), the product CO(2) desorption also collimated in an inclined way, whereas the inclined O(2) desorption was suppressed.

Spatial distributions of desorbing products in basic catalytic processes and surface nano-structures.

Reviews of recent progress in angle-resolved measurements of desorbing surface reaction products are discussed. The angular and velocity distributions of desorbing products deliver information about the reaction site as well as the reaction mechanism when the products are repulsively desorbed. These distribution measurements can yield symmetry and orientation information of the reaction site for associative processes whereas, in dissociative desorption, the collimation of fragment desorption is related to the orientation of the intermediate species immediately before dissociation.

A density-functional theory study of the interaction of N2O with Rh110.

The adsorption of nitrous oxide, N2O, on a Rh110 surface has been characterized by using density-functional theory. N2O was found to bind to the surface in two alternative forms. The first, less stable form is tilted with the terminal N atom attached to the surface, while the second, more stable form lies horizontally on the surface.

Desorption of products in 193 nm photo-induced reactions in (O2 + CO) adlayers on Pt(112).

The spatial distributions of desorbing products were examined in 193 nm photo-induced reactions in O2 + CO adlayers on stepped Pt(112) = [(s)3(111) x (001)]. At high coverage of O2(a) and CO(a), both O2 and CO2 desorption collimated closely along the (111) terrace normal. The results were compared with those in thermal CO oxidation, and the origin of the collimation angle shift in the latter is discussed.