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A study report of a classical-trajectory of the dynamics of high-energy collisions between Ar atoms and the [C.sub.2][H.sub.6] and [C.sub.2][F.sub.6] molecules is presented. The results suggest that high-energy collisions between closed-shell species of the natural low-earth-orbit environment and spacecraft could contribute to the observed degradation of polymers that coat spacecraft surfaces.

The unimolecular dissociation dynamics of aluminum clusters following collision with either a rare gas atom or a surface is investigated by classical trajectory simulations with model potentials. The initial vibrational energy and angular momentum distributions resulting from collision, as well as the energy and angular momentum resolved lifetime distributions of excited clusters were determined for both collision-induced dissociation and surface-induced dissociation processes.

Molecular beam scattering techniques are used to explore the energy exchange and thermal accommodation efficiencies of HCl in collisions with long-chain and CH3-terminated self-assembled monolayers (SAM) on gold. The potential energy well between the impinging HCl and the polar surface groups is sufficient enough to trap HCl molecules that would otherwise scatter impulsively from the rigid SAM.

A study of energy transfer in collisions of Ar with methane and perfluoromethane at hyperthermal energies is presented. Quasiclassical trajectory calculations of Ar + CH4 collisions indicate that energy transfer from reagents' translation to internal modes of the alkane molecule is greatly enhanced by fluorination.

Three different quenchers are used for the fluorescence quenching of pyrene as a model to study collision rate constants. It is shown that the reaction rate constant is independent of the nature of the colliding pair.

A quasiclassical trajectory (QCT) study of the molecular dissociation in the OH + O2 reaction for several combinations of rotational and vibrational quantum numbers is presented. The results show that OH dissociation and ozone formation via collisions of vibrationally excited OH and O2 molecules are comparable over the same range of collisional energies and that the title dissociative processes provide extra sources of ozone through a three-body recombination reaction with molecular oxygen.

The dynamics of the gas-phase reaction of H atoms with HCI was investigated experimentally by employing the laser photolysis/vacuum-UV laser-induced fluorescence(LP/VUV-LIF) pump and probe technique. The experimental studies stated that the translationally energetic H atoms with average collision energies of E(sub col)=1.4 and 1.7 eV were generated by pulsed laser photolysis of H(sub 2)S and HBr at 222 nm.

The energy gain in specific rational levels of vibrationally excited H(sub 2)O(010) which resulted from collisions with highly vibrationally excited pyrazine in a low-pressure, 298 K environment are investigated using high-resolution transient infrared absorption spectroscopy of water at Lambda approximately equal to 2.7 mm. The molecular properties of the energy acceptor that influence the relaxation of highly virbationally excited molecules are explored.

The direct collisional energy transfer process of Li*(3p)+H2->Li*(3s)+H2 is investigated under gas cell conditions. The experimental results are in agreement with ab initio theoretical predictions, which shows a strong probability of a biabatic transition making the 3p - 3s quenching easy.

Research was conducted to examine the role of the chaperon mechanism through ArCN or ArH complex formation for the association reaction H + CN + Ar -> HCN + Ar. The objective was to investigate some assumptions with focus on the branch that involves the ArCN van der Waals molecule. Results demonstrate the significance of the chaperon mechanism only at low temperatures. Also, the energy-transfer mechanism was found to dominate for both high and moderate temperatures.

Ion-molecule reactions characterized the connectivity of isomeric sulfide ions, C(sub 2)S(sub 3)(super *+), which have been synthesized by dissociative ionization of 1,2-dithiolo(4,3-c)(1,2)dithiole-3,6-dione, 1,2, dithiolo(4,3-c)(1,2)dithiole-3-one-6-thione and 1,3,4,6-tetrapentalene-2,5-dione. The C-sulfide ethenedithione SCCS(sub 2)(super *+) and the S-sulfide ethenedithione ion SCCSS(super *+) were readily differentiated by the reactions. Ab initio calculations at the G2(MP2,SVP) level support the characterization of the ions.

The first state-resolved energy-dependent observation of supercollision energy transfer over a spectrum of well-denoted initial energies was undertaken using a transient infrared laser absorption spectrometer. The study generated information on the mean energy transferred per collision as a function of the average energy content of a hot molecule. It was discovered that the form of the energy-transfer distribution function remain unchanged with donor energy but the extent of the energy transfer probability increased with higher donor energy.

A new approach is described for measuring absolute rates for molecular collisions along with contributions of strong and weak collisions. The method is used for the collisional relaxation of highly vibrationally excited pyrazine with HOD and the observed collision rate is nearly twice the Lennard-Jones collision rate.

Time-independent quantum mechanical (TIQM) method is used for computing differential and integral cross sections for the exchange reaction [H.sup.-] + [D.sub.2] --> HD + [D.sup.-] and [D.sup.-] + [H.sub.2] --> HD +[H.sup.-] in three dimensions on an accurate ab initio potential energy surface. The time-dependent quantum mechanical (TDQM) reaction cross section values are found to reduce more sharply than the TIQM results with increase in the initial rotational quantum number (j) for the [D.sub.2] molecules in their ground vibrational state for ([H.sup.-], [D.sub.2]) collisions.

The expressions for the configuration-specific collision frequencies and the average line-of-centers collision angles and speeds derived from an ideal binary gas mixture are presented. The study indicates that average line-of-centers quantities are all dependent on the ratio of masses of the two components while the configuration-specific collision frequencies depends on molecular size.

A statistical result of simulation 'measurements' on several configurations-specific parameters, including the configuration-specific collision frequencies is presented. The simulations use single-component systems of hard spherical molecules confined within a spherical boundary.

Transient IR probing of energy gain in C[O.sub.2] is used to investigate the collisional relaxation of highly vibrationally excited 3- and 4-picoline with C[O.sub.2]. The statistical nature of collisional quenching in highly excited molecules is highlighted, even when there is clear evidence that the relaxation occurs via impulsive collisions.

Direct measurements of the gas-phase collisional energy transfer parameters are reported for the deactivation of highly vibrationally excited trans-stilbene molecules. It shows that the deactivation rate of excited trans-stilbene is clearly collider dependent and decreases distinctly with the growing collision efficiency of the larger bath gas molecules.

A mesoscopic multiparticle collision model for fluid dynamics is generalized to incorporate the chemical reactions among species that may diffuse at different rates. The model is also able to incorporate the effects of molecular fluctuations on the reactive dynamics.

A study was conducted to investigate the interaction of small hydrocarbon ions, CD3(super +), CD4(super +), CD5(super +), and their isotopic variants CH(sub n)(super +) and (super 13)CH(sub n)(super +) (n = 3,4,5), with room temperature and heated carbon surfaces, over the collision energy range 16-52 eV. The result shows the ion survival probability to about 10% for CD5(super +) and about 30-60 times smaller (0.2-0.4%) for CD3(super +) and CD4(super +).

A study was conducted to examine the functional nature of the state-specific cross section for electronic quenching sigma(sub Q)(E) in collisions of metastaable noble gas atoms [Ar(super *)((super 3)P(sub 2)) and Kr(super *)((super 3)P(sub 2))] with ground-state water molecules confined to a scattering-gas cell. The result reveals that the nonquenching correction has an important effect on the collision energy dependence.

A study was conducted, by performing quantum chemical calculations on the phenol cation system, to investigate the details of the potential energy surface and to provide the molecular parameters necessary for collision-induced dissociation (CID) cross-section modeling. The result indicates that the CID model correctly takes into account kinetic shifts for a tight transition state when positively identified by quantum chemical calculations.

A study was conducted to investigate the range of attributes of a molecular dynamics model for Ne-atoms colliding with a n-hexylthiolate self-assembled monolayer (SAM)/Au{111} surface, and to determine their affect on the energy-transfer dynamics. The result reveals that a SAM model with only 35 alkyl chains gives the same energy transfer to the Au{111} substrate as do much larger models.

The sculpting of an incoming wave in bimolecular scattering is an effective way of controlling cross sections in bimolecular collisions.

Shape resonances have an essential role in the processes of photoassociation and photoacceleration. They pave for an efficacious way for the manipulation of collision pairs in the electronic ground state by infrared light. Along with the use of sub-picosecond laser pulses, the effect of shape resonances can be employed in controlling the efficiency and the state selectivity of the photoassociation and photoacceleration process. These were gleaned from a quantum dynamical description of an atomic collision pair interacting with the electric field of a short infrared laser pulse.