Interaction Of H2O Research Articles

Size-resolved aerosol composition and its link to hygroscopicity at a forested site in Colorado

Abstract. Aerosol hygroscopicity describes the ability of a particle to take up water and form a cloud droplet. Modeling studies have shown sensitivity of precipitation-producing cloud systems to the availability of aerosol particles capable of serving as cloud condensation nuclei (CCN), and hygroscopicity is a key parameter controlling the number of available CCN. Continental aerosol is typically assumed to have a representative hygroscopicity parameter, κ, of 0.3; however, in remote locations this value can be lower due to relatively large mass fractions of organic components. To further our understanding of aerosol properties in remote areas, we measured size-resolved aerosol chemical composition and hygroscopicity in a forested, mountainous site in Colorado during the six-week BEACHON-RoMBAS (Bio-hydro-atmosphere interactions of Energy, Aerosols, Carbon, H2O, Organics and Nitrogen–Rocky Mountain Biogenic Aerosol Study) campaign. This campaign followed a year-long measurement period at this site, and results from the intensive campaign shed light on the previously reported seasonal cycle in aerosol hygroscopicity. New particle formation events were observed routinely at this site and nucleation mode composition measurements indicated that the newly formed particles were predominantly organic. These events likely contribute to the dominance of organic species at smaller sizes, where aerosol organic mass fractions were between 70 and 90%. Corresponding aerosol hygroscopicity was observed to be in the range κ = 0.15–0.22, with hygroscopicity increasing with particle size. Aerosol chemical composition measured by an aerosol mass spectrometer and calculated from hygroscopicity measurements agreed very well during the intensive study, with an assumed value of κorg = 0.13 resulting in the best agreement.

Chameleonic Nature of Hydroxyheme in Heme Oxygenase and Its Reactivity: A Density Functional Theory Study

Iron hydroxyheme is an intermediate in heme degradation that binds to HO-1 in a five-coordinated fashion wherein the fifth ligand is His25. The structure and reactivity of hydroxyheme have been investigated using the B3LYP*, OPBE, and CASSCF methods with the 6-31+G* and 6-311+G** basis sets. Hydroxyheme [(Im)Fe(II)(POH)] (POH is the hydroxyporphyrin) is readily oxidized to oxophlorin [(Im)Fe(III)(PO)] (PO is the oxophlorin trianion) in the protein heme oxygenase. A computational study in the gas phase has shown that (6)[(Im)Fe(II)(POH)] loses one electron from its a2u orbital in the presence of O2 and produces [(Im)Fe(II)(PO(•))]a2u(PO(•) is the oxophlorin dianion radical) in the sextet ground state with a ferrous keto π-neutral radical structure and dxy(2)a2u(1)dyz(1)dxz(1)σ*z2(1)d(x(2)-y(2))(1) electronic configuration. There is a closely lying exited state accompanying this ferrous keto π-neutral radical that has a high-spin ferric keto anion form of (6)[(Im)Fe(III)(PO)]xy with a2u(2)dxy(1)dyz(1)dxz(1)σ*z2(1)d(x(2)-y(2))(1) electronic configuration. In the protein environment with a dipole moment larger than 5.7, the ground state is reversed and (6)[(Im)Fe(III)(PO)]xy is at least 1.47 kcal/mol lower than the ferrous π-neutral radical of (6)[(Im)Fe(II) (PO(•))]a2u. The interaction of H2O, O2, and CO with iron oxophlorin will shift the electronic structure toward the formation of a keto π-neutral radical resonance form in the following order: CO > O2 > H2O.

Sulfur-bearing phases detected by evolved gas analysis of the Rocknest aeolian deposit, Gale Crater, Mars

The Sample Analysis at Mars (SAM) instrument suite detected SO2, H2S, OCS, and CS2 from ~450 to 800°C during evolved gas analysis (EGA) of materials from the Rocknest aeolian deposit in Gale Crater, Mars. This was the first detection of evolved sulfur species from a Martian surface sample during in situ EGA. SO2 (~3–22 µmol) is consistent with the thermal decomposition of Fe sulfates or Ca sulfites, or evolution/desorption from sulfur-bearing amorphous phases. Reactions between reduced sulfur phases such as sulfides and evolved O2 or H2O in the SAM oven are another candidate SO2 source. H2S (~41–109 nmol) is consistent with interactions of H2O, H2 and/or HCl with reduced sulfur phases and/or SO2 in the SAM oven. OCS (~1–5 nmol) and CS2 (~0.2–1 nmol) are likely derived from reactions between carbon-bearing compounds and reduced sulfur. Sulfates and sulfites indicate some aqueous interactions, although not necessarily at the Rocknest site; Fe sulfates imply interaction with acid solutions whereas Ca sulfites can form from acidic to near-neutral solutions. Sulfides in the Rocknest materials suggest input from materials originally deposited in a reducing environment or from detrital sulfides from an igneous source. The presence of sulfides also suggests that the materials have not been extensively altered by oxidative aqueous weathering. The possibility of both reduced and oxidized sulfur compounds in the deposit indicates a nonequilibrium assemblage. Understanding the sulfur mineralogy in Rocknest materials, which exhibit chemical similarities to basaltic fines analyzed elsewhere on Mars, can provide insight in to the origin and alteration history of Martian surface materials.

Total OH reactivity measurements in ambient air in a southern Rocky mountain ponderosa pine forest during BEACHON-SRM08 summer campaign

Total OH reactivity was measured during the Bio-hydro-atmosphere interactions of Energy, Aerosols, Carbon, H2O, Organics and Nitrogen-Southern Rocky Mountain 2008 field campaign (BEACHON-SRM08) held at Manitou Experimental Forest (MEF) in Colorado USA in August, 2008. The averaged total OH reactivity was 6.7 s−1, smaller than that measured in urban (33.4 s−1, Yoshino et al., 2012) and suburban (27.7 s−1, Yoshino et al., 2006) areas in Tokyo in the same season, while sporadically high OH reactivity was also observed during some evenings. The total OH reactivity measurements were accompanied by observations of traces species such as CO, NO, NOy, O3 and SO2 and Volatile Organic Compounds (VOCs). From the calculation of OH reactivity based on the analysis of these trace species, 46.3% of OH reactivity for VOCs came from biogenic species that are dominated by 2-methyl-3-buten-2-ol (MBO), and monoterpenes. MBO was the most prominent contribution to OH reactivity of all trace species. A comparison of observed and calculated OH reactivity shows that the calculated OH reactivity is 29.5% less than the observed value, implying the existence of missing OH sinks. One of the candidates of missing OH is thought to be the oxidation products of biogenic species.

Density functional theory periodic slab calculations of adsorption and dissociation of H2O on the Cu2O(110):CuO surface

Interaction of water with Cu2O has many prominent industrial and environmental applications. This study represents detailed density-functional theory calculations investigating the adsorption of a water molecule on a Cu2O(110):CuO surface; one of the two most stable Cu2O surfaces under practical catalytic conditions of temperatures and pressures. We report herein structural geometries and binding energies for all plausible molecular and dissociative interaction of H2O with the surface. The water molecule is found to interact weakly with the Cu2O(110):CuO surface, forming several vertical and flat orientations where the latter was found to offer the most preferred site with a binding energy at 0.389 eV. Dissociation of a water molecule on this surface is found to incur a modest endothermcity of 0.71 eV.

Exact quantum scattering calculations of transport properties for the H2O–H system

Transport properties for collisions of water with hydrogen atoms are computed by means of exact quantum scattering calculations. For this purpose, a potential energy surface (PES) was computed for the interaction of rigid H2O, frozen at its equilibrium geometry, with a hydrogen atom, using a coupled-cluster method that includes all singles and doubles excitations, as well as perturbative contributions of connected triple excitations. To investigate the importance of the anisotropy of the PES on transport properties, calculations were performed with the full potential and with the spherical average of the PES. We also explored the determination of the spherical average of the PES from radial cuts in six directions parallel and perpendicular to the C2 axis of the molecule. Finally, the computed transport properties were compared with those computed with a Lennard-Jones 12-6 potential.

Calculation of vapor–liquid equilibrium and PVTx properties of geological fluid system with SAFT-LJ EOS including multi-polar contribution. Part III. Extension to water–light hydrocarbons systems

The SAFT-LJ EOS improved by Sun and Dubessy (2010, 2012) is extended to water–light hydrocarbon systems. Light hydrocarbons (including CH4, C2H6, C3H8 and nC4H10) are modeled as chain molecules without multi-polar moments. The contributions of the shape of molecules and main intermolecular interactions existing in water–light hydrocarbon systems (including repulsive and attractive forces between Lennard-Jones segments, the hydrogen-bonding force and the multi-polar interaction between water molecules) to the residual Helmholtz energy were accounted for by this EOS. The adjustable parameters for the interactions of H2O–CH4, H2O–C2H6, H2O–C3H8, and H2O–nC4H10 pairs were evaluated from mutual solubility data of binary water–hydrocarbon systems at vapor–liquid equilibria. Comparison with the experimental data shows this SAFT-LJ EOS can represent well vapor–liquid (and liquid–liquid) equilibria of binary water–light hydrocarbon systems over a wide P–T range. The accuracy of this EOS for mutual solubilities of methane, ethane, propane and water is within the experimental uncertainty generally. Moreover, the model is able to accurately predict the vapor–liquid equilibria and PVTx properties of multi-component systems composed of water, light hydrocarbon as well as CO2. As we know, this EOS is the first one allowing quantitative calculation of the mutual solubilities of water and light hydrocarbons over a wide P–T range among SAFT-type EOSs. This work indicates that the molecular-based EOS combined with conventional mixing rule can well describe the thermodynamic behavior of highly non-ideal systems such as water–light hydrocarbons mixtures except in the critical region for which long range density fluctuations cannot be taken into account by this analytical model.

Enhancing air stability of pentacene-based OTFTs with pentacene double layer

A new technique called a pentacene double layer is proposed in this paper to enhance the air stability of the pentacene-based OTFTs. A practically insulating amorphous layer of pentacene (P-II) deposited at very low substrate temperature is used as protective layer above the pentacene active layer (P-I) so that an encapsulation layer of SiO2 can be deposited without damaging the active layer. This technique reduced the probability of interaction of O2 and H2O with the active pentacene layer to zero during fabrication of the devices (multiple breakdown process), and hence can be fabricated without using nitrogen ambient chamber as a result the devices become highly cost effective.

Theoretical Study of H2O Adsorption on Zn2GeO4 Surfaces: Effects of Surface State and Structure–Activity Relationships

We employed the density functional theory to investigate the interaction of H2O with Zn2GeO4 surfaces, considering both perfect and defective surfaces. The results revealed that the interaction of H2O with Zn2GeO4 surfaces was dependent on the structure of the latter. For perfect surfaces, H2O adsorbed at the Ge3c···O2c site of a (010) surface could spontaneously dissociate into an H atom and an OH group, whereas H2O tended to adsorb at the O2c-M3c-O3c site of a (001) surface by molecular adsorption. The presence of oxygen defects was found to strongly promote H2O dissociation on the (010) surface. Analysis of the surface electronic structure showed a large density of Ge states at the top of the valence band for both perfect and defective (010) surfaces, which is an important factor affecting H2O dissociation. In contrast, perfect and defective (001) surfaces with surface Ge states buried inside the valence band were significantly less reactive, and H2O was adsorbed on these surfaces in the molecular form. This information about the adsorbate geometries, catalytic activity of various surface sites, specific electronic structure of surface Ge atoms, and their relevance to surface structure will be useful for the future design of the Zn2GeO4 photocatalyst, as well as for the atomistic-level understanding of other structure-sensitive reactions.

The interaction of H2O with the surface of polycrystalline gadolinium at the temperature range of 300–570 K

The interaction of water vapor with polycrystalline gadolinium surface, in the temperature range of 300–570K and water vapor pressure from 2×10−8 and up to 18Torr, was studied by utilizing Direct-Recoil-Spectrometry, X-ray Photoelectron Spectroscopy and Temperature Programmed Desorption. It has been found that a native Gd surface compound as well as one that was formed by an exposure to 18Torr H2O, for 10min, consists of a multilayer hydroxide phase, Gd(OH)3, transforming into oxide at the metal interface by heating, while emitting hydrogen. For initial exposures of water vapor on a clean metallic surface, it has been deduced that initially, full dissociation of the water molecules on the metal surface occurs, for ~1–2L at 300K and up to ~3L at 570K. On top of the formed oxide there is dissociation to H+OH and hydroxyls are adsorbed, forming, with further exposure, a multilayer hydroxide phase. Enhanced inward diffusion of oxygen starts as early as 370K (similar to the case of oxygen exposure).

Surface science investigations of the role of CO 2 in astrophysical ices

We have recorded reflection-absorption infrared spectroscopy (RAIRS) and temperature-programmed desorption (TPD) data for a range of CO₂-bearing model astrophysical ices adsorbed on a graphitic dust grain analogue surface. Data have been recorded for pure CO₂, for CO₂ adsorbed on top of amorphous solid water, for mixed CO₂:H₂O ices and for CO₂ adsorbed on top of a mixed CH₃OH:H₂O ice. For the TPD data, kinetic parameters for desorption have been determined, and the trapping behaviour of the CO₂ in the H₂O (CH₃OH) ice has been determined. Data of these types are important as they can be used to model desorption in a range of astrophysical environments. RAIR spectra have also shown the interaction of the CO₂ with H₂O and CH₃OH and can be used to compare with astronomical observations, allowing the accurate assignment of spectra.

Adsorption of atmospheric oxidants at divacancy sites of graphene: A DFT study

Periodic DFT calculations are performed to compare the reactivity with respect to atmospheric oxidants like O2, H2O, O3 and atomic oxygen of different divacancy structures created in graphene sheet by removing two adjacent carbon atoms. The present approach shows that O and O3 can easily be chemisorbed at the divacancy sites, the reaction product being however strongly dependent on the divacancy structure. The situation appears more intricate when considering the interaction of O2 and H2O with the defective graphene sheet. In this case, dissociative chemisorption on the surface is evidenced only when dangling bonds are present at the divacancy site.

Enabling Nucleophilic Substitution Reactions of Activated Alkyl Fluorides through Hydrogen Bonding

It was discovered that the presence of water as a cosolvent enables the reaction of activated alkyl fluorides for bimolecular nucleophilic substitution reactions. DFT calculations show that activation proceeds through stabilization of the transition structure by a stronger F···H2O interaction and diminishing C-F bond elongation, and not simple transition state electrostatic stabilization. Overall, the findings put forward a distinct strategy for C-F bond activation through H-bonding.

Fundamental studies about the interaction of water with perfect, oxygen-vacancy and pre-covered oxygen Cu2O(1 1 1) surfaces: Thermochemistry, barrier, product

The adsorption and dissociation of H2O on three types of Cu2O(111) surfaces, including perfect, oxygen-vacancy and pre-covered oxygen surfaces have been systematically investigated using periodic density functional slab model calculations. Different kinds of possible modes of H2O adsorbed on those surfaces are identified. Our results first show that the bonding of dissociated species (HO, H and O) for H2O is substantially stronger than that of H2O on Cu2O(111) surface. Then, on perfect surface, H2O mainly exist in the form of molecular adsorption, in which CuCUS site is chemisorption, OSUF site is physisorption with a weak hydrogen bond. On oxygen-vacancy surface, dissociative adsorption of H2O occurs predominantly, suggesting that oxygen-vacancy exhibits a strong catalytic activity toward H2O dissociation; meanwhile, a small quantity of chemisorption H2O adsorbed at CuCUS site also exists. On pre-covered oxygen surface, H2O is typical of physisorption due to a hydrogen bond interaction between H of adsorbed H2O and pre-covered oxygen. Further, the dissociation mechanisms of molecular adsorption H2O, OH from dissociative adsorption H2O, as well as single OH group on different surfaces, leading to the final products H and O atoms, give out the thermochemistry, barrier of each elementary reaction, which indicates that OH species is energetically the most stable product on those surfaces. Pre-covered oxygen on Cu2O(111) surface can act as a promoter to facilitate the first dehydrogenation of molecular adsorption H2O leading to OH species, which is more favorable both thermodynamically and kinetically than that of molecular adsorption H2O on other two surfaces. Finally, the vibrational frequencies for the adsorbed H2O and OH species on Cu2O(111) surfaces can be applied to guide surface vibrational spectroscopy in experiment. Our calculation may be a worthwhile theoretical example for the interaction of H2O with other metal oxide surface.

Communication: covalent nature of X⋯H2O (X = F, Cl, and Br) interactions.

Open-shell halogen (X = F, Cl, Br) atoms form entrance-channel complexes with H2O, which play an important role in the X + H2O reactions. To understand their structures and origin of stability, we report an extensive ab initio study of such complexes and contrast them with complexes between H2O and H/O((3)P). Evidence is presented to show that the interaction between a halogen atom and H2O is dominated by a weak but covalent bond, rather than dispersion and/or electrostatic interactions.

Application of the transverse acoustoelectric effect to studying silicon surface charging upon water adsorption

Water adsorption on a silicon surface in a layered Si-LiNbO3 structure with an air gap is studied using the transverse acoustoelectric effect on surface acoustic waves. A generalized analysis of measurements of the transverse acoustoelectric effect makes it possible to determine the initial band bending of the Si surface, its changes during gas cycles, hence, the sign and charging kinetics of Si upon H2O adsorption. Depending on the properties of the semiconductor surface defects, both the donor and acceptor nature of the interaction of H2O with Si are observed. For samples with a thermal oxide, the donor-type interaction occurs; for samples with a natural oxide, both interaction types take place. Based on the used physical model of oxide charging upon exposure to an adsorbate, a comprehensive methodical approach is proposed, which allows the targeted development of acoustoelectronic structures for sensor applications.

Reactivity of Hydroxyls and Water on a CeO2(111) Thin Film Surface: The Role of Oxygen Vacancy

The interaction of atomic hydrogen and H2O with stoichiometric and partially reduced CeO2(111) thin films deposited on a Cu(111) substrate was investigated by temperature programmed desorption and ...

Evaluation of HO<sub>x</sub> sources and cycling using measurement-constrained model calculations in a 2-methyl-3-butene-2-ol (MBO) and monoterpene (MT) dominated ecosystem

Abstract. We present a detailed analysis of OH observations from the BEACHON (Bio-hydro-atmosphere interactions of Energy, Aerosols, Carbon, H2O, Organics and Nitrogen)-ROCS (Rocky Mountain Organic Carbon Study) 2010 field campaign at the Manitou Forest Observatory (MFO), which is a 2-methyl-3-butene-2-ol (MBO) and monoterpene (MT) dominated forest environment. A comprehensive suite of measurements was used to constrain primary production of OH via ozone photolysis, OH recycling from HO2, and OH chemical loss rates, in order to estimate the steady-state concentration of OH. In addition, the University of Washington Chemical Model (UWCM) was used to evaluate the performance of a near-explicit chemical mechanism. The diurnal cycle in OH from the steady-state calculations is in good agreement with measurement. A comparison between the photolytic production rates and the recycling rates from the HO2 + NO reaction shows that recycling rates are ~20 times faster than the photolytic OH production rates from ozone. Thus, we find that direct measurement of the recycling rates and the OH loss rates can provide accurate predictions of OH concentrations. More importantly, we also conclude that a conventional OH recycling pathway (HO2 + NO) can explain the observed OH levels in this non-isoprene environment. This is in contrast to observations in isoprene-dominated regions, where investigators have observed significant underestimation of OH and have speculated that unknown sources of OH are responsible. The highly-constrained UWCM calculation under-predicts observed HO2 by as much as a factor of 8. As HO2 maintains oxidation capacity by recycling to OH, UWCM underestimates observed OH by as much as a factor of 4. When the UWCM calculation is constrained by measured HO2, model calculated OH is in better agreement with the observed OH levels. Conversely, constraining the model to observed OH only slightly reduces the model-measurement HO2 discrepancy, implying unknown HO2 sources. These findings demonstrate the importance of constraining the inputs to, and recycling within, the ROx radical pool (OH + HO2 + RO2).

The effect of water on the hydrogenation of o-chloronitrobenzene in ethanol, n-heptane and compressed carbon dioxide

Water as a clean solvent and promoter in the organic synthesis have attracted more attention, herein the effect of water was studied for the hydrogenation of o-chloronitrobenzene (o-CNB) over Pt/C and Pd/C catalysts in ethanol, n-heptane and compressed CO2. Very interesting, the reaction rate decreased in ethanol, but increased in n-heptane and compressed CO2 with the addition of water. The role of water in the reaction was mainly discussed from the experimental data and phase behavior analysis, one is to activate the functional group of NO2 through the interactions via a hydrogen bonding, and the other is to affect the solubility of hydrogen in ethanol and n-heptane. The positive effect of the interaction between water and reactants may be counteracted by the negative effect of hydrogen solubility in ethanol. However, the concentration of o-CNB and hydrogen changed slightly in n-heptane with the addition of water, so the interaction of water with reactants may play a main role in improving the TOF. The combination of H2O and CO2 is more efficient than the pure H2O, CO2 and H2O–n-heptane systems. The phase behavior may play important role also for the improved activity except for the interactions of H2O and CO2 with the reactants. o-CNB phase was expanded in the compressed CO2 and so the concentration of H2 in o-CNB phase increased due to the miscible of CO2 and H2, resulting in the enhancement of reaction rate and the maximum conversion at pressure of 9MPa CO2, at which the volume was expanded to the largest one. The similar results were also obtained in the compressed CO2 system without H2O. In addition, the stability of Pt/C and Pd/C was studied in H2O–n-heptane and H2O–CO2. As a result, the H2O–CO2 media and Pt/C catalyst is one of the most effective systems for the hydrogenation of o-CNB.

Reactivity of metal oxide clusters with hydrogen peroxide and water – a DFT study evaluating the performance of different exchange–correlation functionals

We have performed a density functional theory (DFT) investigation of the interactions of H2O2, H2O and HO radicals with clusters of ZrO2, TiO2 and Y2O3. Different modes of H2O adsorption onto the clusters were studied. In almost all the cases the dissociative adsorption is more exothermic than molecular adsorption. At the surfaces where H2O has undergone dissociative adsorption, the adsorption of H2O2 and the transition state for its decomposition are mediated by hydrogen bonding with the surface HO groups. Using the functionals B3LYP, B3LYP-D and M06 with clusters of 26 and 8 units of ZrO2, the M06 functional performed better than B3LYP in describing the reaction of decomposition of H2O2 and the adsorption of H2O. Additionally, we investigated clusters of the type (ZrO2)2, (TiO2)2 and (Y2O3) and the performance of the functionals B3LYP, B3LYP-D, B3LYP*, M06, M06-L, PBE0, PBE and PWPW91 in describing H2O2, H2O and HO˙ adsorption and the energy barrier for decomposition of H2O2. The trends obtained for HO˙ adsorption onto the clusters are discussed in terms of the ionization energy of the metal cation present in the oxide. In order to correctly account for the existence of an energy barrier for the decomposition of H2O2, the functional used must include Hartree-Fock exchange. Using minimal cluster models, the best performance in describing the energy barrier for H2O2 decomposition was obtained with the M06 and PBE0 functionals - the average absolute deviations from experiments are 6 kJ mol(-1) and 5 kJ mol(-1) respectively. With the M06 functional and a larger monoclinic (ZrO2)8 cluster model, the performance is in excellent agreement with experimental data. For the different oxides, PBE0 was found to be the most effective functional in terms of performance and computational time cost.