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Molecular beam experiments and molecular dynamics simulations have been used to assess the dynamics of argon beam collisions with water ice at 110 K to 180 K. It is suggested that molecules with a mass similar to Ar will trap on particles with a high probability under stratospheric conditions.

Molecular beam-surface scattering was used to investigate collisions of HC1 with ice surfaces which found the major outcome of the HC1-ice collisions was sticking.

Experiments were performed to describe the cluster-surface collision dynamics. The kinetics of water cluster collisions on graphite surfaces was examined. Angular distributions for negative cluster ions were measured at surface temperatures of 1280-1450 K. The findings demonstrate sharply peaked angular distributions close to the tangential direction. During the surface interaction, the water clusters conserved 65-85% of their velocity parallel to the surface plane. The surface normal direction recorded a velocity of 75-100 m/s independent of incident angle.

A highly surface sensitive technique based on elastic scattering of low-energy helium atoms has been used to probe the conditions in the topmost molecular layer on ice in the temperature range of 150–191 K. The elastically scattered intensity decreased slowly as the temperature was increased to about 180 K, followed by a rapid decrease at higher temperatures. An effective surface Debye temperature of 185±10 K was calculated from the data below 180 K. The changes in the ice surface above 180 K are interpreted as the onset of an anomalous enhancement of the mean square vibrational amplitude for the surface molecules and/or the onset of a limited amount of disorder in the ice surface. The interpretation is consistent with earlier experimental studies and molecular dynamics simulations. The observed changes above 180 K can be considered as the first sign of increased mobility of water molecules in the ice surface, which ultimately leads to the formation of a quasiliquid layer at higher temperatures. A small shift and broadening of the specular peak was also observed in the range of 150–180 K and the effect is explained by the inherent corrugation of the crystalline ice surface. The peak shift became more pronounced with increasing temperature, which indicates that surface corrugation increases as the temperature approaches 180 K. The results have implications for the properties and surface chemistry of atmospheric ice particles, and may contribute to the understanding of solvent effects on the internal molecular motion of hydrated proteins and other organic structures such as DNA. [ABSTRACT FROM AUTHOR]

Dissociative recombination (DR) of the dimer ion (NO)2+ has been studied at the heavy-ion storage ring CRYRING at the Manne Siegbahn Laboratory, Stockholm. The experiments were aimed at determining details on the strongly enhanced thermal rate coefficient for the dimer, interpreting the dissociation dynamics of the dimer ion, and studying the degree of similarity to the behavior in the monomer. The DR rate reveals that the very large efficiency of the dimer rate with respect to the monomer is limited to electron energies below 0.2 eV. The fragmentation products reveal that the breakup into the three-body channel NO+O+N dominates with a probability of 0.69±0.02. The second most important channel yields NO+NO fragments with a probability of 0.23±0.03. Furthermore, the dominant three-body breakup yields electronic and vibrational ground-state products, NO(υ=0)+N(4S)+O(3P), in about 45% of the cases. The internal product-state distribution of the NO fragment shows a similarity with the product-state distribution as predicted by the Franck-Condon overlap between a NO moiety of the dimer ion and a free NO. The dissociation dynamics seem to be independent of the NO internal energy. Finally, the dissociation dynamics reveal a correlation between the kinetic energy of the NO fragment and the degree of conservation of linear momentum between the O and N product atoms. The observations support a mechanism in which the recoil takes place along one of the NO bonds in the dimer. [ABSTRACT FROM AUTHOR]

The emission of neutral cluster fragments during collisions of large water clusters with graphite surfaces has been investigated using molecular beam techniques. Water clusters with an average size of up to 1.4·10[sup 4] molecules per cluster collide with the surface with a velocity of 1380 ms-1. Angular distributions for emitted large fragments are shifted towards the tangential direction and become increasingly narrow with increasing fragment size. The kinetic energy in the surface normal direction is efficiently transferred to internal degrees of freedom and to surface modes, while the momentum parallel to the surface plane is less affected by the surface interaction. Both a direct scattering channel and an emission channel mediated by cluster evaporation are concluded to be of importance for the collision outcome. The results for the evaporation-mediated emission channel agree well with previous experimental investigations and with recent molecular dynamics simulations, and the observations regarding the direct scattering channel qualitatively agree with the dynamics observed for macroscopic particles colliding with surfaces. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Large-scale classical molecular-dynamics simulations of (H[sub 2]O)[sub n] (n=1032,4094) collisions with graphite have been carried out. The clusters have an initial internal temperature of 180 K and collide with an incident velocity in the normal direction between 200 and 1000 m/s. The 1032-clusters are trapped on the surface and completely disintegrate by evaporation. The 4094-clusters are found to partly survive the surface impact provided that the surface is sufficiently hot. These clusters are trapped on the surface for up to 50 ps before leaving the surface under strong evaporation of small fragments. The time spent on the surface is too short for full equilibration to occur, which limits the fragmentation of the clusters. The size of the emitted fragment is roughly 30% of the incident cluster size. The cluster emission mechanism is found to be very sensitive to the rate of the surface-induced heating and thus to the surface temperature. The incident cluster velocity is less critical for the outcome of the collision process but influences the time spent on the surface. The trends seen in the simulations agree well with recent experimental data for collisions of large water clusters with graphite [Chem. Phys. Lett. 329, 200 (2000)]. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The molecular beam method is used to investigate the kinetics of Cl (sub 2) interactions with ice at temperatures ranging from 103 to 165 K. It was observed that the chlorine is adsorbed at thermal kinetic energies, a minimum of two varying adsorption states on the surface affects the desoprtion behavior, the activation energies are likely to be the chlorine -ice binding energies for these states, chlorine-surface interaction is stronger than estimated and surface coverage of chlorine on ice under stratospheric conditions is negligible.

Examines the scattering and trapping dynamics of xenon-graphite interaction. Details on the coupling between atom translation and surface modes; Lack of structural corrugation effects at high kinetic energies; Calculation of stochastic trajectory to simulate the scattering of xenon atoms.