Jianming Zhang

Publications (21)91.24 Total impact

• Article: Product-state-resolved dynamics of the elementary reaction of atomic oxygen with molecular hydrogen, O((3)P) + D2 → OD(X(2)Π) + D.

  Sridhar A Lahankar, Jianming Zhang, Kenneth G McKendrick, Timothy K Minton
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  ABSTRACT: Elementary three-atom systems provide stringent tests of the accuracy of ab initio theory. One such important reaction, O((3)P) + H2 → OH(X(2)Π) + H, has eluded detailed experimental study because of its high activation barrier. In this reaction, both the ground-state reactant atom and product diatomic molecule have open-shell character, which introduces the intriguing complication of non-Born-Oppenheimer effects in both the entrance and the exit channels. These effects may be probed experimentally in both the fine-structure and the Λ-doublet splittings of the OH product. We have used laser-induced fluorescence to measure OD internal product-state distributions from the analogous reaction of O((3)P) with D2, enabled by a unique high-energy O((3)P) source. We find that the OD (ν' = 0) product is rotationally highly excited, in excellent agreement with earlier theoretical predictions. However, the distributions over the OD(X(2)Π) fine-structure and Λ-doublet states, diagnostic of electronic non-adiabaticity in the reaction, challenge the prevailing theoretical understanding.
  Nature Chemistry 04/2013; 5(4):315-9. · 20.52 Impact Factor
• Article: Kinematics and dynamics of atomic-beam scattering on liquid and self-assembled monolayer surfaces.

  William A Alexander, Jianming Zhang, Vanessa J Murray, Gilbert M Nathanson, Timothy K Minton
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  ABSTRACT: We have conducted investigations of the energy transfer dynamics of atomic oxygen and argon scattering from hydrocarbon and fluorocarbon surfaces. In light of these results, we appraise the applicability and value of a kinematic scattering model, which views a gas-surface interaction as a gas-phase-like collision between an incident atom or molecule and a localized region of the surface with an effective mass. We have applied this model to interpret the effective surface mass and energy transfer when atoms strike two different surfaces under identical bombardment conditions. To this end, we have collected new data, and we have re-examined existing data sets from both molecular-beam experiments and molecular dynamics simulations. We seek to identify trends that could lead to a robust general understanding of energy transfer processes induced by collisions of gas-phase species with liquid and semi-solid surfaces.
  Faraday Discussions 01/2012; 157:355-74; discussion 375-98. · 5.00 Impact Factor
• Article: Atomic oxygen effects on POSS polyimides in low earth orbit.

  Timothy K Minton, Michael E Wright, Sandra J Tomczak, Sara A Marquez, Linhan Shen, Amy L Brunsvold, Russell Cooper, Jianming Zhang, Vandana Vij, Andrew J Guenthner, Brian J Petteys
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  ABSTRACT: Kapton polyimde is extensively used in solar arrays, spacecraft thermal blankets, and space inflatable structures. Upon exposure to atomic oxygen in low Earth orbit (LEO), Kapton is severely eroded. An effective approach to prevent this erosion is to incorporate polyhedral oligomeric silsesquioxane (POSS) into the polyimide matrix by copolymerizing POSS monomers with the polyimide precursor. The copolymerization of POSS provides Si and O in the polymer matrix on the nano level. During exposure of POSS polyimide to atomic oxygen, organic material is degraded, and a silica passivation layer is formed. This silica layer protects the underlying polymer from further degradation. Laboratory and space-flight experiments have shown that POSS polyimides are highly resistant to atomic-oxygen attack, with erosion yields that may be as little as 1% those of Kapton. The results of all the studies indicate that POSS polyimide would be a space-survivable replacement for Kapton on spacecraft that operate in the LEO environment.
  ACS Applied Materials & Interfaces 12/2011; 4(2):492-502. · 4.53 Impact Factor
• Article: O(3P) + CO2 collisions at hyperthermal energies: dynamics of nonreactive scattering, oxygen isotope exchange, and oxygen-atom abstraction.

  Laurence Y Yeung, Mitchio Okumura, Jianming Zhang, Timothy K Minton, Jeffrey T Paci, Amir Karton, Jan M L Martin, Jon P Camden, George C Schatz
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  ABSTRACT: The dynamics of O((3)P) + CO(2) collisions at hyperthermal energies were investigated experimentally and theoretically. Crossed-molecular-beams experiments at <E(coll)> = 98.8 kcal mol(-1) were performed with isotopically labeled (12)C(18)O(2) to distinguish products of nonreactive scattering from those of reactive scattering. The following product channels were observed: elastic and inelastic scattering ((16)O((3)P) + (12)C(18)O(2)), isotope exchange ((18)O + (16)O(12)C(18)O), and oxygen-atom abstraction ((18)O(16)O + (12)C(18)O). Stationary points on the two lowest triplet potential energy surfaces of the O((3)P) + CO(2) system were characterized at the CCSD(T)/aug-cc-pVTZ level of theory and by means of W4 theory, which represents an approximation to the relativistic basis set limit, full-configuration-interaction (FCI) energy. The calculations predict a planar CO(3)(C(2v), (3)A'') intermediate that lies 16.3 kcal mol(-1) (W4 FCI excluding zero point energy) above reactants and is approached by a C(2v) transition state with energy 24.08 kcal mol(-1). Quasi-classical trajectory (QCT) calculations with collision energies in the range 23-150 kcal mol(-1) were performed at the B3LYP/6-311G(d) and BMK/6-311G(d) levels. Both reactive channels observed in the experiment were predicted by these calculations. In the isotope exchange reaction, the experimental center-of-mass (c.m.) angular distribution, T(θ(c.m.)), of the (16)O(12)C(18)O products peaked along the initial CO(2) direction (backward relative to the direction of the reagent O atoms), with a smaller isotropic component. The product translational energy distribution, P(E(T)), had a relatively low average of <E(T)> = 35 kcal mol(-1), indicating that the (16)O(12)C(18)O products were formed with substantial internal energy. The QCT calculations give c.m. P(E(T)) and T(θ(c.m.)) distributions and a relative product yield that agree qualitatively with the experimental results, and the trajectories indicate that exchange occurs through a short-lived CO(3)* intermediate. A low yield for the abstraction reaction was seen in both the experiment and the theory. Experimentally, a fast and weak (16)O(18)O product signal from an abstraction reaction was observed, which could only be detected in the forward direction. A small number of QCT trajectories leading to abstraction were observed to occur primarily via a transient CO(3) intermediate, albeit only at high collision energies (149 kcal mol(-1)). The oxygen isotope exchange mechanism for CO(2) in collisions with ground state O atoms is a newly discovered pathway through which oxygen isotopes may be cycled in the upper atmosphere, where O((3)P) atoms with hyperthermal translational energies can be generated by photodissociation of O(3) and O(2).
  The Journal of Physical Chemistry A 12/2011; 116(1):64-84. · 2.95 Impact Factor
• Article: Crossed-beams studies of the dynamics of the H-atom abstraction reaction, O(3P) + CH4 → OH + CH3, at hyperthermal collision energies.

  Jianming Zhang, Sridhar A Lahankar, Donna J Garton, Timothy K Minton, Weiqing Zhang, Xueming Yang
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  ABSTRACT: The H-atom abstraction reaction, O((3)P) + CH(4) → OH + CH(3), has been studied at a hyperthermal collision energy of 64 kcal mol(-1) by two crossed-molecular-beams techniques. The OH products were detected with a rotatable mass spectrometer employing electron-impact ionization, and the CH(3) products were detected with the combination of resonance-enhanced multiphoton ionization (REMPI) and time-sliced ion velocity-map imaging. The OH products are mainly formed through a stripping mechanism, in which the reagent O atom approaches the CH(4) molecule at large impact parameters and the OH product is scattered in the forward direction: roughly the same direction as the reagent O atoms. Most of the available energy is partitioned into product translation. The dominance of the stripping mechanism is a unique feature of such H-atom abstraction reactions at hyperthermal collision energies. In the hyperthermal reaction of O((3)P) with CH(4), the H-atom abstraction reaction pathway accounts for 70% of the reactive collisions, while the H-atom elimination pathway to produce OCH(3) + H accounts for the other 30%.
  The Journal of Physical Chemistry A 09/2011; 115(40):10894-902. · 2.95 Impact Factor
• Source

  Available from: colorado.edu

  Article: Protecting polymers in space with atomic layer deposition coatings.

  Timothy K Minton, Bohan Wu, Jianming Zhang, Ned F Lindholm, Aziz I Abdulagatov, Jennifer O'Patchen, Steven M George, Markus D Groner
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  ABSTRACT: Polymers in space may be subjected to a barrage of incident atoms, photons, and/or ions. Atomic layer deposition (ALD) techniques can produce films that mitigate many of the current challenges for space polymers. We have studied the efficacy of various ALD coatings to protect Kapton polyimide, FEP Teflon, and poly(methyl methacrylate) films from atomic-oxygen and vacuum ultraviolet (VUV) attack. Atomic-oxygen and VUV studies were conducted with the use of a laser-detonation source for hyperthermal O atoms and a D2 lamp as a source of VUV light. These studies used a quartz crystal microbalance (QCM) to monitor mass loss in situ, as well as surface profilometry and scanning electron microscopy to study the surface recession and morphology changes ex situ. Al2O3 ALD coatings protected the underlying substrates from atomic-oxygen attack, and the addition of TiO2 coatings protected the substrates from VUV-induced damage. The results indicate that ALD coatings can simultaneously protect polymers from oxygen-atom erosion and VUV radiation damage.
  ACS Applied Materials & Interfaces 09/2010; 2(9):2515-20. · 4.53 Impact Factor
• Article: Scattering Dynamics of Hyperthermal Oxygen Atoms on Ionic Liquid Surfaces: [emim][NTf2] and [C12mim][NTf2]

  Bohan Wu, Jianming Zhang, Timothy K. Minton
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  ABSTRACT: Collisions of hyperthermal oxygen atoms, with an average laboratory-frame translational energy of 520 kJ mol−1, on continuously refreshed ionic liquids, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([emim][NTf2]) and 1-dodecyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([C12mim][NTf2]), were studied with the use of a beam-surface scattering technique. Time-of-flight and angular distributions of inelastically scattered O and reactively scattered OH and H2O were collected for various angles of incidence with the use of a rotatable mass spectrometer detector. For both O and OH, two distinct scattering processes were identified, which can be empirically categorized as thermal and nonthermal. Nonthermal scattering is more probable for both O and OH products. The observation of OH confirms that at least some reactive sites, presumably alkyl groups, must be exposed at the surface. The ionic liquid with the longer alkyl chain, [C12mim][NTf2], is substantially more reactive than the liquid with the shorter alkyl chain, [emim][NTf2], and proportionately much more so than would be predicted simply from stoichiometry based on the number of abstractable hydrogen atoms. Molecular dynamics models of these surfaces shed light on this change in reactivity. The scattering behavior of O is distinctly different from that of OH. However, no such differences between inelastic and reactive scattering dynamics have been seen in previous work on pure hydrocarbon liquids, in particular, the benchmark, partially branched hydrocarbon, squalane (C30H62). The comparison between inelastic and reactive scattering dynamics indicates that inelastic scattering from the ionic liquid surfaces takes place predominantly at nonreactive sites that are effectively stiffer than the reactive alkyl chains, with a higher proportion of collisions sampling such sites for [emim][NTf2] than for [C12mim][NTf2].
  03/2010;
• Article: Crossed-beams and theoretical studies of hyperthermal reactions of O(3P) with HCl.

  Jianming Zhang, Amy L Brunsvold, Hari P Upadhyaya, Timothy K Minton, Jon P Camden, Sophya Garashchuk, George C Schatz
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  ABSTRACT: The reaction of O((3)P) with HCl at hyperthermal collision energies (45-116 kcal mol(-1)) has been investigated with crossed-molecular beams experiments and direct dynamics quasi-classical trajectory calculations. The reaction may proceed by two primary pathways, (1) H-atom abstraction to produce OH and Cl and (2) H-atom elimination to produce H and ClO. The H-atom abstraction reaction follows a stripping mechanism, in which the reagent O atom approaches the HCl molecule at large impact parameters and the OH product is scattered in the forward direction, defined as the initial direction of the reagent O atoms. The H-atom elimination reaction is highly endoergic and requires low-impact-parameter collisions. The excitation function for ClO increases from a threshold near 45 kcal mol(-1) to a maximum around 115 kcal mol(-1) and then begins to decrease when the ClO product can be formed with sufficient internal energy to undergo secondary dissociation. At collision energies slightly above threshold for H-atom elimination, the ClO product scatters primarily in the backward direction, but as the collision energy increases, the fraction of these products that scatter in the forward and sideways directions increases. The dependence of the angular distribution of ClO on collision energy is a result of the differences in collision geometry. Collisions where the H atom on HCl is oriented away from the incoming reagent O atom lead to backward-scattered ClO and those where the H atom is oriented toward the incoming O atom lead to forward-scattered ClO. The latter trajectories do not follow the minimum energy path and involve larger translational energy release. Therefore, they become dominant at higher collision energies because they lead to lower internal energies and more stable ClO products. The H-atom abstraction and elimination reactions have comparable cross sections for hyperthermal O((3)P) + HCl collisions.
  The Journal of Physical Chemistry A 03/2010; 114(14):4905-16. · 2.95 Impact Factor
• Article: Hyperthermal O-atom exchange reaction O2 + CO2 through a CO4 intermediate.

  Laurence Y Yeung, Mitchio Okumura, Jeffrey T Paci, George C Schatz, Jianming Zhang, Timothy K Minton
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  ABSTRACT: O(2) and CO(2) do not react under ordinary conditions because of the thermodynamic stability of CO(2) and the large activation energy required for multiple double-bond cleavage. We present evidence for a gas-phase O-atom exchange reaction between neutral O(2) and CO(2) at elevated collision energies (approximately 160 kcal mol(-1)) from crossed-molecular-beam experiments. CCSD(T)/aug-cc-pVTZ calculations demonstrate that isotope exchange can occur on the ground triplet potential energy surface through a short-lived CO(4) intermediate that isomerizes via a symmetric CO(4) transition state containing a bridging oxygen atom. We propose a plausible adiabatic mechanism for this reaction supported by additional spin-density calculations.
  Journal of the American Chemical Society 10/2009; 131(39):13940-2. · 9.91 Impact Factor
• Article: Theoretical and experimental studies of the reactions between hyperthermal O(3P) and graphite: graphene-based direct dynamics and beam-surface scattering approaches.

  Jeffrey T Paci, Hari P Upadhyaya, Jianming Zhang, George C Schatz, Timothy K Minton
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  ABSTRACT: Beam-surface scattering experiments and theoretical direct dynamics based on density functional theory calculations are used to investigate hyperthermal collisions between O((3)P) and highly oriented pyrolytic graphite (HOPG). The simulations suggest that the HOPG surface becomes functionalized with epoxide groups. Intersystem crossing (ISC) between the lowest-energy triplet and singlet potential-energy surfaces is not necessary for this functionalization to occur. Both theory and experiment indicate that incoming O atoms can react at the surface to form O(2) by way of an Eley-Rideal mechanism. They also suggest that the collisions can result in the production of CO and CO(2) by way of both direct and complex reaction mechanisms. The direct dynamics simulations provide significant insight into the details of the complex reaction mechanisms. Semiquinones are present at defect sites and can form in functionalized pristine sheets, the latter resulting in the formation of a defect. Direct collision of an incoming O atom with a semiquinone or vibrational excitation caused by a nearby O-atom collision can cause the release of the semiquinone CO, forming carbon monoxide. The CO may react with an oxygen atom on the surface to become CO(2) before receding from the surface. The simulations also illustrate how epoxide groups neighboring semiquinones catalyze the release of CO. Throughout, the experimental results are observed to be consistent with the theoretical calculations.
  The Journal of Physical Chemistry A 04/2009; 113(16):4677-85. · 2.95 Impact Factor
• Article: Erosion of FEP Teflon and PMMA by VUV radiation and hyperthermal O or Ar atoms.

  Jianming Zhang, Ned F Lindholm, Amy L Brunsvold, Hari P Upadhyaya, Timothy K Minton, Masahito Tagawa
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  ABSTRACT: A combination of beam-surface-scattering, quartz-crystal-microbalance, and surface-recession experiments was conducted to study the effects of various combinations of O atoms [in the O((3)P) ground state], Ar atoms, and vacuum ultraviolet (VUV) light on fluorinated ethylene-propylene copolymer (FEP) Teflon and poly(methyl methacrylate) (PMMA). A laser-breakdown source was used to create hyperthermal beams containing O and O(2) or Ar. A D(2) lamp provided a source of VUV light. O atoms with 4 eV of translational energy or less did not react with a pristine FEP Teflon surface. Volatile O-containing reaction products were observed when the O-atom energy was higher than 4.5 eV, and the signal increased with the O-atom energy. Significant erosion of FEP Teflon ( approximately 20% of Kapton H) was observed when it was exposed to the hyperthermal O/O(2) beam with an average O-atom energy of 5.4 eV. FEP Teflon and PMMA that were exposed to VUV light alone exhibited much less mass loss. Collision-induced dissociation by hyperthermal Ar atoms also caused mass loss, similar in magnitude to that caused by VUV light. There were no observed synergistic effects when VUV light or Ar bombardment was combined with O/O(2) exposure. For both FEP Teflon and PMMA, the erosion yields caused by simultaneous exposure to O/O(2) and either VUV light or Ar atoms could be approximately predicted by adding the erosion yield caused by O/O(2), acting individually, to the erosion yield caused by the individual action of either VUV light or Ar atoms.
  ACS Applied Materials & Interfaces 03/2009; 1(3):653-60. · 4.53 Impact Factor
• Article: Protection of Polymers from the Space Environment by Atomic Layer Deposition

  Ned F. Lindholm, Jianming Zhang, Timothy K. Minton, Jennifer O’Patchen, Steven M. George, Markus D. Groner
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  ABSTRACT: Polymers in space may be subjected to a barrage of incident atoms, photons, and∕or ions. For example, oxygen atoms can etch and oxidize these materials. Photons may act either alone or in combination with oxygen atoms to degrade polymers and paints and thus limit their usefulness. Colors fade under the intense vacuum ultraviolet (VUV) solar radiation. Ions can lead to the build‐up of static charge on polymers. Atomic layer deposition (ALD) techniques can provide coatings that could mitigate many challenges for polymers in space. ALD is a gas‐phase technique based on two sequential, self‐limiting surface reactions, and it can deposit very uniform, conformal, and pinhole‐free films with atomic layer control. We have studied the efficacy of various ALD coatings to protect Kapton® polyimide, FEP Teflon®, and poly(methyl methacrylate) films from atomic‐oxygen and VUV attack. Atomic‐oxygen and VUV studies were conducted with the use of a laser‐breakdown source for hyperthermal O atoms and a D2 lamp as a source of VUV light. These studies used a quartz crystal microbalance (QCM) to monitor mass loss in situ, as well as surface profilometry and scanning electron microscopy to study the surface recession and morphology changes ex situ. Al2O3 ALD coatings applied to polyimide and FEP Teflon® films protected the underlying substrates from O‐atom attack, and ZnO coatings protected the poly(methyl methacrylate) substrate from VUV‐induced damage.
  AIP Conference Proceedings. 01/2009; 1087(1):407-418.
• Article: Beam-surface scattering studies of the individual and combined effects of VUV radiation and hyperthermal O, O2, or Ar on FEP Teflon surfaces.

  Amy L Brunsvold, Jianming Zhang, Hari P Upadhyaya, Timothy K Minton
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  ABSTRACT: Beam-surface scattering experiments were used to probe products that scattered from FEP Teflon surfaces during bombardment by various combinations of atomic and molecular oxygen, Ar atoms, and vacuum ultraviolet (VUV) light. A laser-breakdown source was used to create hyperthermal (translational energies in the range 4-13 eV) beams of argon and atomic/molecular oxygen. The average incidence energy of these beams was tunable and was controlled precisely with a synchronized chopper wheel. A filtered deuterium lamp provided a source of VUV light in a narrow-wavelength range centered at 161 nm. Volatile products that exited the surfaces were monitored with a rotatable mass spectrometer detector. Hyperthermal O atoms with average translational energies above approximately 4 eV may react directly with a pristine FEP Teflon surface, and the reactivity appears to increase with the translational energy of the incident O atoms. VUV light or highly energetic collisions of O2 or Ar may break chemical bonds and lead to the ejection of volatile products; the ejection of volatile products is enhanced when the surface is subjected to VUV light and energetic collisions simultaneously. Exposure to VUV light or to hyperthermal O2 or Ar may increase the reactivity of an FEP Teflon surface to O atoms.
  ACS Applied Materials & Interfaces 01/2009; 1(1):187-96. · 4.53 Impact Factor
• Source

  Available from: Amy Brunsvold

  Article: Unusual mechanisms can dominate reactions at hyperthermal energies: an example from O(3P) + HCl --> ClO + H.

  Jianming Zhang, Jon P Camden, Amy L Brunsvold, Hari P Upadhyaya, Timothy K Minton, George C Schatz
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  ABSTRACT: An unusual mechanism in the reaction, O(3P) + HCl --> ClO + H, dominates at hyperthermal collision energies. This mechanism applies to collision geometries in which the H atom in the HCl molecule is oriented toward the reagent O atom. As the Cl-O bond forms, the H atom experiences a strong repulsive force from both the O and Cl atoms. The ClO product scatters forward with respect to the initial velocity of the O atom, and the H atom scatters backward. This mechanism accounts for more than half the reactive trajectories at energies >110 kcal mol-1, but it does not involve motion near the minimum energy path, which favors an SN2-like reaction mechanism where the H atom is oriented away from the reagent O atom during the collision.
  Journal of the American Chemical Society 08/2008; 130(28):8896-7. · 9.91 Impact Factor
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  Available from: Amy Brunsvold

  Article: Hyperthermal Ar atom scattering from a C(0001) surface.

  K D Gibson, S J Sibener, Hari P Upadhyaya, Amy L Brunsvold, Jianming Zhang, Timothy K Minton, Diego Troya
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  ABSTRACT: Experiments and simulations on the scattering of hyperthermal Ar from a C(0001) surface have been conducted. Measurements of the energy and angular distributions of the scattered Ar flux were made over a range of incident angles, incident energies (2.8-14.1 eV), and surface temperatures (150-700 K). In all cases, the scattering is concentrated in a narrow superspecular peak, with significant energy exchange with the surface. The simulations closely reproduce the experimental observations. Unlike recent experiments on hyperthermal Xe scattering from graphite [Watanabe et al., Eur. Phys. J. D 38, 103 (2006)], the angular dependence of the energy loss is not approximated by the hard cubes model. The simulations are used to investigate why parallel momentum conservation describes Xe scattering, but not Ar scattering, from the surface of graphite. These studies extend our knowledge of gas-surface collisional energy transfer in the hyperthermal regime, and also demonstrate the importance of performing realistic numerical simulations for modeling such encounters.
  The Journal of chemical physics 07/2008; 128(22):224708. · 3.09 Impact Factor
• Article: Dynamics of hyperthermal collisions of O(3P) with CO.

  Amy L Brunsvold, Hari P Upadhyaya, Jianming Zhang, Russell Cooper, Timothy K Minton, Matthew Braunstein, James W Duff
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  ABSTRACT: The dynamics of O(3P) + CO collisions at a hyperthermal collision energy near 80 kcal mol-1 have been studied with a crossed molecular beams experiment and with quasi-classical trajectory calculations on computed potential energy surfaces. In the experiment, a rotatable mass spectrometer detector was used to monitor inelastically and reactively scattered products as a function of velocity and scattering angle. From these data, center-of-mass (c.m.) translational energy and angular distributions were derived for the inelastic and reactive channels. Isotopically labeled C18O was used to distinguish the reactive channel (16O + C18O 16OC + 18O) from the inelastic channel (16O + C18O 16O + C18O). The reactive 16OC molecules scattered predominantly in the forward direction, i.e., in the same direction as the velocity vector of the reagent O atoms in the c.m. frame. The c.m. translational energy distribution of the reactively scattered 16OC and 18O was very broad, indicating that 16OC is formed with a wide range of internal energies, with an average internal excitation of approximately 40% of the available energy. The c.m. translational energy distribution of the inelastically scattered C18O and 16O products indicated that an average of 15% of the collision energy went into internal excitation of C18O, although a small fraction of the collisions transferred nearly all the collision energy into internal excitation of C18O. The theoretical calculations, which extend previously published results on this system, predict c.m. translational energy and angular distributions that are in near quantitative agreement with the experimentally derived distributions. The theoretical calculations, thus validated by the experimental results, have been used to derive internal state distributions of scattered CO products and to probe in detail the interactions that lead to the observed dynamical behavior.
  The Journal of Physical Chemistry A 04/2008; 112(11):2192-205. · 2.95 Impact Factor
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  Available from: google.com

  Article: Crossed-beams and theoretical studies of the O((3)P) + H(2)O --> HO(2) + H reaction excitation function.

  Amy L Brunsvold, Jianming Zhang, Hari P Upadhyaya, Timothy K Minton, Jon P Camden, Jeffrey T Paci, George C Schatz
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  ABSTRACT: Hyperthermal collisions of ground-state atomic oxygen with H2O have been investigated, with special attention paid to the H-atom elimination reaction, O((3)P) + H(2)O(X (1)A(1)) --> HO(2)((2)A') + H((2)S). This reaction was observed in a crossed-beams experiment, and the relative excitation function in the region around its energy threshold (50-80 kcal mol(-1)) was measured. Direct dynamics calculations were also performed at two levels of theory, B3LYP/6-31G(d,p) and MP2/6-31G(d,p). The shape of the B3LYP excitation function closely matches that of the experiment. The calculations provided a detailed description of the dynamics and revealed a striking dependence of the reaction mechanism on collision energy, where the cross section rises from a threshold near 60 kcal mol(-1) to a peak at approximately 115 kcal mol(-1) and then decreases at higher energies as secondary dissociation of the internally excited HO(2) product becomes dominant. The calculations show that the cross section for H-atom elimination (O + H(2)O --> HO(2) + H) is about 10-25% that of the H-atom abstraction (O + H(2)O --> OH + OH) cross section for collision energies in the 70-160 kcal mol(-1) range.
  The Journal of Physical Chemistry A 11/2007; 111(43):10907-13. · 2.95 Impact Factor
• Article: Crossed-Beams and Theoretical Studies of the O(3P) + H2O → HO2 + H Reaction Excitation Function

  Amy L. Brunsvold, Jianming Zhang, Hari P. Upadhyaya, Timothy K. Minton
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  ABSTRACT: Hyperthermal collisions of ground-state atomic oxygen with H2O have been investigated, with special attention paid to the H-atom elimination reaction, O(3P) + H2O(X 1A1) → HO2(2A‘) + H(2S). This reaction was observed in a crossed-beams experiment, and the relative excitation function in the region around its energy threshold (50−80 kcal mol-1) was measured. Direct dynamics calculations were also performed at two levels of theory, B3LYP/6-31G(d,p) and MP2/6-31G(d,p). The shape of the B3LYP excitation function closely matches that of the experiment. The calculations provided a detailed description of the dynamics and revealed a striking dependence of the reaction mechanism on collision energy, where the cross section rises from a threshold near 60 kcal mol-1 to a peak at 115 kcal mol-1 and then decreases at higher energies as secondary dissociation of the internally excited HO2 product becomes dominant. The calculations show that the cross section for H-atom elimination (O + H2O → HO2 + H) is about 10−25% that of the H-atom abstraction (O + H2O → OH + OH) cross section for collision energies in the 70−160 kcal mol-1 range.
  10/2007;
• Article: Hyperthermal reactions of O and O2 with a hydrocarbon surface: direct C-C bond breakage by O and H-atom abstraction by O2.

  Jianming Zhang, Hari P Upadhyaya, Amy L Brunsvold, Timothy K Minton
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  ABSTRACT: A C-C bond-breaking reaction has been observed when a beam containing hyperthermal oxygen was directed at a continuously refreshed saturated hydrocarbon liquid (squalane) surface. The dynamics of this C-C bond-breaking reaction have been investigated by monitoring time-of-flight and angular distributions of the volatile product, OCH3 or H2CO. The primary product is believed to be the methoxy radical, OCH3, but if this radical is highly internally excited, then it may undergo secondary dissociation to form formaldehyde, H2CO. Either the primary or the secondary product may scatter directly into the gas phase before thermal equilibrium with the surface is reached, or they may become trapped on the surface and desorb in thermal equilibrium with the surface. Direct, single-collision scattering events that produce a C-C bond-breaking product are described with a kinematic picture that allows the determination of the effective surface mass encountered by an incident O atom, the atom-surface collision energy in the center-of-mass frame, and the fraction of the center-of-mass collision energy that goes into translation of the scattered gaseous product and the recoiling surface fragment. The dynamical behavior of the C-C bond-breaking reaction is compared with that of the H-atom abstraction reaction, which was the subject of an earlier study. Another reaction, H-atom abstraction by O2 (which is present in the hyperthermal beam), has also been observed, and the dynamics of this reaction are compared with the inelastic scattering dynamics of O2 and the dynamics of H-atom abstraction by O. The dynamics involving direct inelastic and reactive scattering of O2 are also described in terms of a kinematic picture where the incident O2 molecule is viewed as interacting with a local region of the surface.
  The Journal of Physical Chemistry B 07/2006; 110(25):12500-11. · 3.70 Impact Factor
• Article: Reactive and inelastic scattering dynamics of hyperthermal oxygen atoms on a saturated hydrocarbon surface

  Jianming Zhang, Donna J. Garton, Timothy K. Minton
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  ABSTRACT: The dynamics of the initial interactions of hyperthermal O atoms with a saturated hydrocarbon surface have been investigated by directing an O-atom beam at a continuously refreshed liquid squalane surface and monitoring time-of-flight and angular distributions of inelastically scattered O atoms and reactively scattered OH and H2O. These products are formed through thermal and nonthermal processes. The inelastic scattering processes may be described in terms of the limiting cases of direct inelastic scattering (nonthermal) and trapping desorption (thermal). The initial step leading to production of volatile OH and H2O is believed to be direct H-atom abstraction to form OH. Once formed, the OH may scatter directly into the gas phase before thermal equilibrium with the surface is reached, or it may undergo further collisions and reactions with the surface. These secondary interactions include trapping and desorption of OH and abstraction of a second hydrogen atom to form H2O. Interactions that occur before thermal equilibrium with the surface can be reached lead to products that exit the surface at hyperthermal velocities, while those that occur in thermal equilibrium with the surface yield products that leave the surface at thermal velocities given by the surface temperature. Direct, single-collision scattering events that produce O and OH are described with a kinematic picture that allows the determination of the effective surface mass encountered by an incident O atom, the atom–surface collision energy in the center-of-mass frame, and the fraction of the center-of-mass collision energy that goes into translation of the scattered gaseous product and the recoiling surface fragment. Center-of-mass velocity-flux maps for OH indicate either single-collision events through a largely collinear O–H–C transition state or multiple-collision events in which initially formed OH scatters inelastically from the surface. © 2002 American Institute of Physics.
  The Journal of Chemical Physics 09/2002; 117(13):6239-6251. · 3.33 Impact Factor