Deducing Reaction and Diffusion Depths of Near-Interfacial Solvated Electrons from pH-Dependent Product Evaporation.

Near-interfacial electrons in water can be produced by bombarding an aqueous microjet in vacuum with gas-phase sodium atoms. These Na atoms immediately ionize into Na and e, which can then react with surface-active molecules that preferentially populate the surface. We carried out these experiments by reacting e with the surfactant benzyltrimethylammonium (BTMA) in a 6.

Probing the interfacial structure of aqueous surfactants through helium atom evaporation.

Dissolved helium atoms evaporate from liquids in super-Maxwellian speed distributions because their interactions are too weak to enforce full thermal equilibration at the surface as they are "squeezed" out of solution. The excess speeds of these He atoms reflect their final interactions with solvent and solute molecules at the surfaces of water and other liquids. We extend this observation by monitoring He atom evaporation from salty water solutions coated with surfactants.

Molecular Insights into Chemical Reactions at Aqueous Aerosol Interfaces.

Atmospheric aerosols facilitate reactions between ambient gases and dissolved species. Here, we review our efforts to interrogate the uptake of these gases and the mechanisms of their reactions both theoretically and experimentally. We highlight the fascinating behavior of NO in solutions ranging from pure water to complex mixtures, chosen because its aerosol-mediated reactions significantly impact global ozone, hydroxyl, and methane concentrations.

Creation and Reaction of Solvated Electrons at and near the Surface of Water.

Solvated electrons (e) are among nature's most powerful reactants, with over 2600 reactions investigated in bulk water. These electrons can also be created at and near the surface of water by exposing an aqueous microjet in vacuum to gas-phase sodium atoms, which ionize into e and Na within the top few layers. When a reactive surfactant is added to the jet, the surfactant and e become coreactants localized in the interfacial region.

Weak Temperature Dependence of the Relative Rates of Chlorination and Hydrolysis of NO in NaCl-Water Solutions.

We have measured the temperature dependence of the ClNO product yield in competition with hydrolysis following NO uptake to aqueous NaCl solutions. For NaCl-DO solutions spanning 0.0054-0.

Exploring Gas-Liquid Reactions with Microjets: Lessons We Are Learning.

Liquid water is all around us: at the beach, in a cloud, from a faucet, inside a spray tower, covering our lungs. It is fascinating to imagine what happens to a reactive gas molecule as it approaches the surface of water in these examples. Some incoming molecules may first be deflected away after colliding with an evaporating water molecule.

The Wisconsin Oscillator: A Low-Cost Circuit for Powering Ion Guides, Funnels, and Traps.

In this work, we present the Wisconsin Oscillator, a small, inexpensive, low-power circuit for powering ion-guiding devices such as multipole ion guides, ion funnels, active ion-mobility devices, and non-mass-selective ion traps. The circuit can be constructed for under $30 and produces two antiphase RF waveforms of up to 250 V in the high kilohertz to low megahertz range while drawing less than 1 W of power. The output amplitude is determined by a 0-6.

Competing Segregation of Br and Cl to a Surface Coated with a Cationic Surfactant: Direct Measurements of Ion and Solvent Depth Profiles.

Ion-surface scattering experiments can be used to measure elemental depth profiles on the angstrom scale in complex liquid mixtures. We employ NICISS (neutral impact collision ion scattering spectroscopy) to measure depth profiles of dissolved ions and solvent in liquid glycerol containing the cationic surfactant tetrahexylammonium bromide (THA/Br) at 0.013 M and mixtures of NaBr + NaCl at 0.

Experimental Depth Profiles of Surfactants, Ions, and Solvent at the Angstrom Scale: Studies of Cationic and Anionic Surfactants and Their Salting Out.

Neutral impact ion scattering spectroscopy (NICISS) is used to measure the depth profiles of ionic surfactants, counterions, and solvent molecules on the angstrom scale. The chosen surfactants are 0.010 tetrahexylammonium bromide (THA/Br) and 0.

S2 Reactions of NO with Ions in Water: Microscopic Mechanisms, Intermediates, and Products.

Reactions of dinitrogen pentoxide (NO) greatly affect the concentrations of NO, ozone, OH radicals, methane, and more. In this work, we employ ab initio molecular dynamics and other tools of computational chemistry to explore reactions of NO with anions hydrated by 12 water molecules to shed light on this important class of reactions. The ions investigated are Cl, SO, ClO, and RCOO (R = H, CH, CH).

Production of Br from NO and Br in Salty and Surfactant-Coated Water Microjets.

Gas-liquid scattering experiments are used to investigate the oxidation-reduction reaction NO(g) + 2Br(aq) → Br(g) + NO(aq) + NO(aq), a model for the nighttime absorption of NO into aerosol droplets containing halide ions. The detection of evaporating Br molecules provides our first observation of a gaseous reaction product generated by a water microjet in vacuum. NO molecules are directed at a 35 μm diameter jet of 6 or 8 LiBr in water at 263 or 240 K, followed by detection of both unreacted NO and product Br molecules by velocity-resolved mass spectrometry.

Ab initio molecular dynamics studies of formic acid dimer colliding with liquid water.

Ab initio molecular dynamics simulations of formic acid (FA) dimer colliding with liquid water at 300 K have been performed using density functional theory. The two energetically lowest FA dimer isomers were collided with a water slab at thermal and high kinetic energies up to 68kBT. Our simulations agree with recent experimental observations of nearly a complete uptake of gas-phase FA dimer: the calculated average kinetic energy of the dimers immediately after collision is 5 ± 4% of the incoming kinetic energy, which compares well with the experimental value of 10%.

Control of Interfacial Cl and NO Reactivity by a Zwitterionic Phospholipid in Comparison with Ionic and Uncharged Surfactants.

Gas-liquid scattering experiments reveal that charge-separated but neutral (zwitterionic) surfactants catalyze the oxidation of dissolved Br to Br by gaseous Cl at the surface of a 0.3 M NaBr/glycerol solution. Solutions of NaBr dissolved in glycerol with no surfactant were compared with solutions coated with zwitterionic, cationic, and anionic surfactants at dilute surface concentrations of 1.

NO at water surfaces: binding forces, charge separation, energy accommodation and atmospheric implications.

Interactions of N2O5 with water media are of great importance in atmospheric chemistry and have been the topic of extensive research for over two decades. Nevertheless, many physical and chemical properties of N2O5 at the surface or in bulk water are unknown or not microscopically understood. This study presents extensive new results on the physical properties of N2O5 in water and at the surface of water, with a focus on their microscopic basis.

Reactions of NO with Salty and Surfactant-Coated Glycerol: Interfacial Conversion of Br to Br Mediated by Alkylammonium Cations.

Gas-liquid scattering and product-yield experiments are used to investigate reactions of NO with glycerol containing Br and surfactant ions. NO oxidizes Br to Br for every solution tested: 2.7 M NaBr, 0.

Deprotonation of formic acid in collisions with a liquid water surface studied by molecular dynamics and metadynamics simulations.

Deprotonation of organic acids at aqueous surfaces has important implications in atmospheric chemistry and other disciplines, yet it is not well-characterized or understood. This article explores the interactions of formic acid (FA), including ionization, in collisions at the air-water interface. Ab initio molecular dynamics simulations with dispersion-corrected density functional theory were used.

Microjets and coated wheels: versatile tools for exploring collisions and reactions at gas-liquid interfaces.

This tutorial review describes experimental aspects of two techniques for investigating collisions and reactions at the surfaces of liquids in vacuum. These gas-liquid scattering experiments provide insights into the dynamics of interfacial processes while minimizing interference from vapor-phase collisions. We begin with a historical survey and then compare attributes of the microjet and coated-wheel techniques, developed by Manfred Faubel and John Fenn, respectively, for studies of high- and low-vapor pressure liquids in vacuum.

Gas-Microjet Reactive Scattering: Collisions of HCl and DCl with Cool Salty Water.

Liquid microjets provide a powerful means to investigate reactions of gases with salty water in vacuum while minimizing gas-vapor collisions. We use this technique to explore the fate of gaseous HCl and DCl molecules impinging on 8 molal LiCl and LiBr solutions at 238 K. The experiments reveal that HCl or DCl evaporate infrequently if they become thermally accommodated at the surface of either solution.

Super-Maxwellian helium evaporation from pure and salty water.

Helium atoms evaporate from pure water and salty solutions in super-Maxwellian speed distributions, as observed experimentally and modeled theoretically. The experiments are performed by monitoring the velocities of dissolved He atoms that evaporate from microjets of pure water at 252 K and 4-8.5 molal LiCl and LiBr at 232-252 K.

DCl Transport through Dodecyl Sulfate Films on Salty Glycerol: Effects of Seawater Ions on Gas Entry.

Gas-liquid scattering experiments were employed to measure the entry and dissociation of the acidic gas DCl into salty glycerol coated with dodecyl sulfate ions (DS(-) = CH3(CH2)11OSO3(-)). Five sets of salty solutions were examined: 0.25 and 0.

Ballistic Evaporation and Solvation of Helium Atoms at the Surfaces of Protic and Hydrocarbon Liquids.

Atomic and molecular solutes evaporate and dissolve by traversing an atomically thin boundary separating liquid and gas. Most solutes spend only short times in this interfacial region, making them difficult to observe. Experiments that monitor the velocities of evaporating species, however, can capture their final interactions with surface solvent molecules.

Selective photoelectrochemical reduction of aqueous CO₂ to CO by solvated electrons.

Reduction of CO2 by direct one-electron activation is extraordinarily difficult because of the -1.9 V reduction potential of CO2. Demonstrated herein is reduction of aqueous CO2 to CO with greater than 90% product selectivity by direct one-electron reduction to CO2(˙-) by solvated electrons.