Collisions between gases and high vapor pressure liquids can be investigated by coupling narrow diameter liquid jets with gas-surface scattering experiments. In these initial studies, we monitor the scattering of Ar, Ne, and O 2 from liquid dodecane (C 12 H 26 , P vap = 0.1 Torr at 295 K) and from a reference liquid, squalane (C 30 H 62 , P vap = 10 −7 Torr). Collisions of Ar with a cylindrical squalane jet and a flat squalane film reveal similar scattering patterns despite differences in geometry. Further studies indicate that 50 kJ mol −1 Ne atoms scatter impulsively upon collision and transfer ∼55% of their energy to each liquid. Higher values are found for O 2 collisions, where the overall energy transfer is 70−75% of the 30 kJ mol −1 incident energy. These studies imply that hot gases readily transfer their excess translational energy to liquid alkanes in processes such as the heating and evaporation of fuel droplets. SECTION: Kinetics and Dynamics

Solvated electrons are powerful reagents in the liquid phase that break chemical bonds and thereby create additional reactive species, including hydrogen atoms. We explored the distinct chemistry that ensues when electrons are liberated near the liquid surface rather than within the bulk. Specifically, we detected the products resulting from exposure of liquid glycerol to a beam of sodium atoms. The Na atoms ionized in the surface region, generating electrons that reacted with deuterated glycerol, C(3)D(5)(OD)(3), to produce D atoms, D(2), D(2)O, and glycerol fragments. Surprisingly, 43 ± 4% of the D atoms traversed the interfacial region and desorbed into vacuum before attacking C-D bonds to produce D(2).

The binary mutual neutralization (MN) of a series of 17 cations (O₂⁺, NO(+), NO₂⁺, CO(+), CO₂⁺, Cl(+), Cl₂⁺, SO₂⁺, CF₃⁺, C₂F₅⁺, NH₃⁺, H₃⁺, D₃⁺, H2O(+), H3O(+), ArH(+), ArD(+)) with 3 halide anions (Cl(-), Br(-), I(-)) has been investigated in a flowing afterglow-Langmuir probe apparatus using the variable electron and neutral density attachment mass spectrometry technique. The MN rate constants of atom-atom reactions are dominated by the chemical nature of the system (i.e., the specific locations of curve crossings). As the number of atoms in the system increases, the MN rate constants become dominated instead by the physical nature of the system (e.g., the relative velocity of the reactants). For systems involving 4 or more atoms, the 300 K MN rate constants are well described by 2.7 × 10(-7) μ(-0.5), where the reduced mass is in Da and the resulting rate constants in cm(3) s(-1). An upper limit to the MN rate constants appears well described by the complex potential model described by Hickman assuming a cross-section to neutralization of 11,000 Å(2) at 300 K, equivalent to 3.5 × 10(-7) μ(-0.5).

Thermal electron attachment rate coefficients for three interhalogen compounds (ClF, ICl, IBr) have been measured from 300 to 900 K at pressures of 1-2 Torr using a flowing afterglow-Langmuir probe apparatus. ClF attaches somewhat inefficiently (k = 7.5×10 −9 cm 3 s −1 ) at 300 K, with the rate coefficient rising to 1.7×10 −8 cm 3 s −1 at 700 K. At higher temperatures the apparent rate coefficient falls steeply; however, this is interpreted as an artifact due to decomposition on the walls of the inlet line. ICl attaches with even lower efficiency (k = 9.5×10 −10 cm 3 s −1 at 300 K) and a less steep increase with temperature. Attachment to IBr is too slow to confidently measure with the present experiment, with an upper limit on the rate coefficient of 10 −10 cm 3 s −1 from 300 to 600 K. Both ClF and ICl attach dissociatively to yield Cl − , likely exclusively, though F − or I − may be produced with limits of <2% and <5%, respectively. The ClF attachment was further explored through ab initio calculation of the ClF and ClF − potential energy curves and R-matrix calculations of the resonance parameters which were used then for calculations of the dissociative attachment cross sections and rate coefficients. While the magnitude of the attachment rate coefficient for ClF is similar to those for both Cl 2 and F 2 , the calculated cross sections show qualitatively different threshold behavior due to the s-wave contribution allowed by the lack of inversion symmetry. The v = 1 and 2 vibrational modes of ClF attach about three to four times faster than v = 0 and 3 at energies lower than ∼0.2 eV. The calculated rate coefficients are in good agreement with the experiment at 300 K and increase moderately less steeply with temperature.

The reactive uptake and ionization of sodium atoms in glycerol were investigated by gas-liquid scattering experiments and ab initio molecular dynamics (AIMD) simulations. A nearly effusive beam of Na atoms at 670 K was directed at liquid glycerol in vacuum, and the scattered Na atoms were detected by a rotatable mass spectrometer. The Na velocity and angular distributions imply that all impinging Na atoms that thermally equilibrate on the surface remain behind, likely ionizing to e(-) and Na(+). The reactive uptake of Na atoms into glycerol was determined to be greater than 75%. Complementary AIMD simulations of Na striking a 17-molecule glycerol cluster indicate that the glycerol hydroxyl groups reorient around the Na atom as it makes contact with the cluster and begins to ionize. Although complete ionization did not occur during the 10 ps simulation, distinct correlations among the extent of ionization, separation between Na(+) and e(-), solvent coordination, and binding energies of the Na atom and electron were observed. The combination of experiments and simulations indicates that Na-atom deposition provides a low-energy pathway for generating solvated electrons in the near-interfacial region of protic liquids.