EMSL: Jim Cowin's Publications

Bell RC, K Wu, MJ Iedema, GK Schenter, and JP Cowin. 2009. "The Oil-Water Interface: Mapping the Solvation Potential." Journal of the American Chemical Society 131(3):1037-1042. doi:10.1021/ja805962x Abstract Ions moving across the oil water interface are strongly impacted by the continuous changes in solvation. The solvation potential for Cs+ is directly measured as they approach the oil-water interface (“oil” = 3-methylpentane), from 0.4 to 4 nm away. The oil-water interfaces are created at 40K using molecular beam epitaxy and a softlanding ion beam, with pre-placed ions. The solvation potential slope was determined at each distance by balancing it against an increasing electrostatic potential made by increasing the number of imbedded ions at that distance, and monitoring the resulting ion motion. The potential approaches the Born model for greater than z>0.4nm, and shows the predicted reduction of the polarizability at z<0.4nm.

Lilach Y, MJ Iedema, and JP Cowin. 2008. "Proton segregation on a Growing Ice Interface." Surface Science 602(17):2886-2893. doi:10.1016/j.susc.2008.07.008 Abstract Hydronium segregates to the surface of H2O (D2O) ice films grown on Pt(111) above 151K (158K). This is observed as from the voltage that develops across the films, utilizing work function measurements. The dependence of this voltage on the film’s thickness is explained by a simple equilibrium model: as the film grows, most of the surface ions migrate so as to remain at the ice-vacuum interface, while a fixed percentage (~0.05%) take the thermodynamically-unfavored route, to become incorporated into the growing bulk ice. This model implies a delta-G of about +0.1eV for the movement of ions from the ice surface into the bulk ice.

Wang H, RC Bell, MJ Iedema, GK Schenter, K Wu, and JP Cowin. 2008. "Pyroelectricity of Water Ice." Journal of Physical Chemistry B 112(20):6379-6389. doi:10.1021/jp073870c Abstract Water ice usually is though to have zero pyroelectricity by symmetry. But biasing it with ions breaks the symmetry because of the induced partially dipole-aligned. This unmasks a large pyroelectricity. Ions were soft-landed upon 1 micron films of water ice at ≥ 160K. When cooled below 140 to 150 K this locks-in the dipole-alignment. Workfunction measurements of these films then show high and reversible pyroelectric activity from 30 to 150K. For an initial ~10V induced by the deposited ions, the at 160K, the observed bias below 150K varies approximately as 10V*(T/150K)2 This implies water has pyroelectric coefficients as large as that of many commercial pyroelectrics such as lead zirconate titanate (“PZT”). The pyroelectricity of water ice, not previously reported, is in reasonable agreement with that predicted via a monte carlo simulation of TIP4P ice. This is observed in crystalline and compact amorphous ice, deuterated or not. This implies that for water ice between 0 and 150K (such as astrophysical ices), temperature changes can induce strong electric fields (~10,000,000 V/m) that can influence their chemistry and trajectories or binding.

Bell RC, K Wu, MJ Iedema, and JP Cowin. 2007. "Hydronium Ion Motion in Nanometer 3-Methyl-pentane Films." Journal of Chemical Physics 127(2):Paper # 024704. doi:10.1063/1.2748756 Abstract An ion soft-landing approach was applied to study the motion of hydronium (D3O+) and cesium (Cs+) ions from 84 to 104 K in glassy 3-methylpentane (3MP) films vapor-deposited on Pt(111). Both ions were found to have very similar mobilities in 3MP. The span of ion mobilities probed is from ~10-18 to ~10-13 m2 V-1 s-1. Ion transport in these films was studied as a function of film thickness and electric field strength. The drift velocity was found to be linear with applied field below about 2 x10(8) V/m, and deviates from linearity above this. To a large extent, D3O+ and Cs+ motion in 3MP was well predicted by a simple continuum-based ion mobility model in films from 25 to 20,000 monolayers thick, (including pronounced perturbations 7 monolayers from both the vacuum and Pt interfaces). The mobility varies with temperature more slowly than predicted by Stokes’ law, which may be due to extended inhomogeneous structures in the 3MP near the 77 K glass transition.

Hadjar O, P Wang, JH Futrell, Y Dessiaterik, Z Zhu, JP Cowin, MJ Iedema, and J Laskin. 2007. "Design and Performance of a Novel Instrument for Soft-Landing of Biomolecular Ions on Surfaces." Analytical Chemistry 79(17):6566-6574. doi:10.1021/ac070600h Abstract A new ion deposition apparatus was designed and constructed in our laboratory. Our research objectives were to investigate interactions of biomolecules with hydrophilic and hydrophobic surfaces and to carry out exploratory experiments aimed at highly-selective deposition of spatially defined and uniquely selected biological molecules on surfaces. The apparatus includes a high-transmission electrospray ion source, quadrupole mass filter, bending quadrupole that deflects the ion beam and prevents neutral molecules originating in the ion source from impacting the surface, an ultrahigh vacuum (UHV) chamber for ion deposition by soft landing, and a vacuum-lock system for introducing surfaces into the UHV chamber without breaking vacuum. Ex situ analysis of surfaces following soft-landing of mass-selected peptide ions was performed using 15 keV Ga+ time-of-flight secondary ion mass spectrometry (TOF-SIMS) and grazing incidence infrared reflection-absorption spectroscopy (IRRAS). It will be shown that these two techniques are highly complementary methods for characterization of surfaces prepared with a range of doses of mass-selected biomolecular ions.

Lilach Y, MJ Iedema, and JP Cowin. 2007. "Dissociation of water buried under ice on Pt(111) ." Physical Review Letters 98(1):Art. No. 016105 . Abstract Water on Pt(111) is generally thought to be non-dissociative. However, by adsorbing a thick ice film (>150 monolayers (ML)), substantial (~0.16 to 1 ML) dissociation of the "buried water" occurs for T > 151K . New temperature-programmed desorption peaks signal the dissociation (after careful isothermal pre-desorption of the overlying ice films). The buried water likely dissociates via the elevated temperatures and/or solvation changes experienced under the ice. Dissociation also creates large work function changes (up to +9V!) due the trapping of ~0.007ML H3O+ at the vacuum-ice interface of the growing ice.

Lilach Y, MJ Iedema, and JP Cowin. 2007. "Reply to Comment on Dissociation of Water Buried Under Ice on Pt(111)." Physical Review Letters 99(10):109602. Abstract [1] on our Letter ‘‘Dissociation of Water Buried under Ice on Pt(111)’’ [2] raises some interesting points. In the original Letter, we made two sets of observations: (1) that thick water films ( > 150 monolayers) absorbed at temperatures higher than usually used in ultrahigh vacuum studies ( > 153 K for H2O) on Pt(111) showed a positive charging that behaved much as would be expected for positive ions trapped on the ice surface during the film growth, and (2) that the thick ice films, when desorbed carefully in a two-step process, showed a consistent pattern of high temperature programmed desorption (TPD) features spanning 170 to 200 K. Based on this, we concluded that water was dissociating at the Pt(111) surface under the thick ice film and in amounts greater than a few tenths of a monolayer. Zimbitas et al. [1] argue that the high temperature peaks can be explained by a nonwetting phenomena that they see for adsorption above 152 K (for H2O), that leads to large water clusters sitting upon a single monolayer of water. Thus, they conclude that our evidence for dissociation of water is weak.

Laskin A, H Wang, WH Robertson, JP Cowin, MJ Ezell, and BJ Finlayson-Pitts. 2006. "A New Approach to Determining Gas-Particle Reaction Probabilities and Application to the Heterogeneous Reaction of Deliquesced Sodium Chloride Particles with Gas-Phase Hydroxyl Radicals." Journal of Physical Chemistry A 110(36):10619-10627. doi:10.1021/jp063263+ Abstract The reaction kinetics for gaseous hydroxyl radicals (OH) with deliquesced sodium chloride particles (NaClaq) were investigated using a novel experimental approach. The technique utilizes the exposure of substrate-deposited aerosol particles to reactive gases followed by chemical analysis of the particles using computer-controlled scanning electron microscopy with energy-dispersive analysis of X-rays (CCSEM/EDX) capability. Experiments were performed at room temperature and atmospheric pressure with deliquesced NaCl particles in the micron size range at 70-80% RH and with OH concentrations in the range of 1 to 7×109 cm-3. The apparent, pseudo first-order rate constant for the reaction was determined from measurements of changes in the chloride concentration of individual particles upon reaction with OH as a function of the particle loading on the substrate. Quantitative treatment of the data using a model that incorporates both diffusion and reaction kinetics yields a lower-limit to the net reaction probability of γnet > 0.1, with an overall uncertainty of a factor of two.

Laskin A, JP Cowin, and MJ Iedema. 2006. "Analysis of Individual Environmental Particles Using Modern Methods of Electron Microscopy and X-Ray Microanalysis." Journal of Electron Spectroscopy and Related Phenomena 150(2-3):260-274. Abstract Understanding the composition of particles in the atmosphere is critical because of their health effects and their direct and indirect effects on radiative forcing, and hence on climate. In this manuscript, we demonstrate the utility of single particle off-line analysis to investigate the chemistry of individual atmospheric particles using modern, state-of-the-art electron microscopy and time-of-flight secondary ionization mass spectrometry techniques. We show that these methods provide specific, detailed data on particle composition, chemistry, morphology, phase and internal structure. This information is crucial for evaluating hygroscopic properties of aerosols, understanding aerosol aging and reactivity, and correlating the characteristics of aerosols with their optical properties. The manuscript presents a number of analytical advances in methods of electron probe particle analysis along with a brief review of a number of the research projects carried out in the authors’ laboratory on the chemical characterization of environmental particles. The obtained data offers a rich set of qualitative and quantitative information on the particle chemistry, composition and the mechanisms of gas-particle interactions which are of high importance to atmospheric processes involving particulate matter and air pollution.

Garrett BC, DA Dixon, DM Camaioni, DM Chipman, MA Johnson, CD Jonah, GA Kimmel, JH Miller, T Rescigno, PJ Rossky, SS Xantheas, SD Colson, AH Laufer, D Ray, PF Barbara, DM Bartels, KH Bowen, KH Becker, SE Bradforth, I Carmichael, JV Coe, LR Corrales, JP Cowin, M Dupuis, KB Eisenthal, JA Franz, MS Gutowski, KD Jordon, BD Kay, JA La Verne, SV Lymar, TE Madey, CW Mccurdy, D Meisel, S Mukamel, AR Nilsson, TM Orlando, NG Petrik, SM Pimblott, JR Rustad, GK Schenter, SJ Singer, A Tokmakoff, LS Wang, C Wittig, and TS Zwier. 2005. "Role of Water in Electron-Initiated Processes and Radical Chemistry: Issues and Scientific Advances." Chemical Reviews 105(1):355-389. doi:10.1021/cr030453x Abstract An understanding of electron-initiated processes in aqueous systems and the subsequent radical chemistry these processes induce is significant in such diverse fields as waste remediation and environmental cleanup, radiation processing, nuclear reactors, and medical diagnosis and therapy. We review the state of the art in the physical chemistry and chemical physics of electron-initiated processes in aqueous systems and raise critical research issues and fundamental questions that remain unanswered.