Dissociation Of HCl Research Articles

XPS and STM studies of the oxidation of hydrogen chloride at Cu(100) surfaces

The dissociative chemisorption of HCl on clean and oxidized Cu(100) surfaces has been investigated using x-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM). Whereas the dissociation of HCl at the clean surface is limited to the formation of a (√2×√2)-R45° Cl(a) monolayer, the presence of surface oxygen removes this barrier, leading to chlorine coverages up to twice that obtained at the clean surface. Additional features in the STM images that appear at these coverages are tentatively assigned to the nucleation of CuCl islands. The rate of reaction of the HCl was slightly higher on the oxidized surface but unaffected by the initial oxygen concentration or the availability of clean copper sites. Of the two distinct domains of adsorbed oxygen identified at room temperature on the Cu(100) surfaces, the (√2×√2)-R45° structure reacts slightly faster with HCl than the missing row (√2×2√2)-R45° O(a) structure. The results address the first stages in the formation of a copper chloride and present an interesting comparison with the HCl/O(a) reaction at Cu(110) surfaces, where oxygen also increased the extent of HCl reactions. The results emphasize the importance of the exothermic reaction to form water in the HCl/O(a) reaction on copper.

Dynamic Reactive Ionization with Cluster Secondary Ion Mass Spectrometry

Gas cluster ion beams (GCIB) have been tuned to enhance secondary ion yields by doping small gas molecules such as CH4, CO2, and O2 into an Ar cluster projectile, Arn + (n = 1000–10,000) to form a mixed cluster. The ‘tailored beam’ has the potential to expand the application of secondary ion mass spectrometry for two- and three-dimensional molecular specific imaging. Here, we examine the possibility of further enhancing the ionization by doping HCl into the Ar cluster. Water deposited on the target surface facilitates the dissociation of HCl. This concerted effect, occurring only at the impact site of the cluster, arises since the HCl is chemically induced to ionize to H+ and Cl– , allowing improved protonation of neutral molecular species. This hypothesis is confirmed by depth profiling through a trehalose thin film exposed to D2O vapor, resulting in ~20-fold increase in protonated molecules. The results show that it is possible to dynamically maintain optimum ionization conditions during depth profiling by proper adjustment of the water vapor pressure. H–D exchange in the trehalose molecule M was monitored upon deposition of D2O on the target surface, leading to the observation of [Mn* + H]+ or [Mn* + D]+ ions, where n = 1–8 hydrogen atoms in the trehalose molecule M have been replaced by deuterium. In general, we discuss the role of surface chemistry and dynamic reactive ionization of organic molecules in increasing the secondary ion yield.

Oxidation mechanism of elemental mercury by HCl over MnO2 catalyst: Insights from first principles

Catalytic oxidation of elemental mercury from flue gas is a promising way in the field of mercury pollution control. Among catalysts for Hg oxidation, MnO2-based materials showed high catalytic activity. The oxidation mechanism of Hg on the MnO2(110) surface was studied by periodic density functional theory calculations. The thermodynamic stability analysis suggests that the stoichiometric MnO2(110) is the most stable surface. Hydroxylation and chlorination MnO2 surfaces can exist under the SCR conditions. The reaction energy profiles of two possible routes (Hg→HgCl→HgCl2 and Hg→HgCl2) and the corresponding configurations were examined. The results show that HCl can undergo dissociative chemisorption to form a surface hydroxyl and manganese–chlorine complex. Hg oxidation reaction occurs through Langmuir–Hinshelwood mechanism in which adsorbed Hg reacts with adsorbed Cl from HCl dissociation. The HgCl2 direct formation on MnO2 (Hg→HgCl2) is hindered by high energy barrier of 98.25 or 101.97kJ/mol. Hg can react with adsorbed Cl with a substantially lower barrier (40.12 or 43.59kJ/mol) to form HgCl, and HgCl can react with adsorbed Cl with a low barrier (57.72 or 66.27kJ/mol) to form HgCl2. The calculated results suggest Hg oxidation by HCl over MnO2 surface prefers the Hg→HgCl→HgCl2 pathway rather than a pathway Hg→HgCl2. The HgCl→HgCl2 process is the rate-determining step for the overall oxidation reaction due to its high energy barrier.

Infrared spectra of HCl(H2O)n clusters from semiempirical Born-Oppenheimer molecular dynamics simulations.

Infrared spectra of HCl(H2O)n clusters, with n = 4-10 and 21, are calculated at T = 50 K from semiempirical Born-Oppenheimer molecular dynamics simulations performed with the PM3-MAIS model. The specific focus of this study is on the relationship between spectroscopic features associated with the presence of the excess proton generated by the HCl dissociation as a function of n and the underlying water hydrogen-bonding topologies. Vibrational modes involving the motion of the excess proton are attributed to specific features appearing at ∼1175 cm(-1) for Zundel-type structures, in the 1670-1800 cm(-1) range for intermediate Zundel-Eigen-type structures, and at ∼2820 cm(-1) for Eigen-type structures. This broad range of vibrational frequencies correlates with the position of the excess proton within the clusters. Overall, the theoretical predictions are in good agreement with the available experimental data.

Investigation of Interfacial and Bulk Dissociation of HBr, HCl, and HNO3 Using Density Functional Theory-Based Molecular Dynamics Simulations

In this study, we calculate free-energy profiles for the dissociation of the strong acids XH (HBr, HCl, and HNO3), specifically, for the deprotonation and subsequent formation of ion pairs, X–···H3O+, in the vicinity of the air–water interface. We show that the free-energy profiles for the dissociation of HCl and HNO3 are significantly different at the air–water interface compared to in the bulk, and we predict that the undissociated, molecular form of these two acids is stable at the interface. For the strongest acid we consider, HBr the traditional picture of completely dissociated strong acids is preserved in the vicinity of the air–water interface. Our results have implications for our understanding of the interfacial chemistry of acids, as well as the effects of acids on the surface tensions of aqueous solutions.

HCl dissociation in methanol clusters from ab initio molecular dynamics simulations and inner-shell photoelectron spectroscopy.

HCl dissociation in methanol clusters is studied by ab initio molecular dynamics simulations and experimentally by X-ray photoelectron spectroscopy. From theoretical simulations of HCl in oligomers and medium-sized clusters of methanol, two states of solvation are identified for HCl: an intermediate proton-sharing (ion pair) state and a fully dissociated state. Lowering the temperature from 150 to 100 K is found to promote full dissociation over the proton-sharing state. The dissociation of HCl is well reflected in the experimental chlorine 2p photoelectron spectrum recorded for a beam of clusters formed by adiabatic expansion of the vapor over a solution of HCl in methanol. In order to reproduce the observed Cl 2p spectrum by means of theoretical line-shape modeling, one needs to take into account both the intermediate proton-sharing state and the fully dissociated state.

Lifetime broadening of atomic lines produced upon ultrafast dissociation of HCl and HBr

Ultrafast dissociation of the HCl and HBr molecules excited respectively to the 2p3/2→σ* and 3d5/2→σ* resonances are studied with high resolution photoelectron spectroscopy. Sharp vibrational molecular lines and broad atomic lines are observed. The analysis of the profile of the atomic lines gives access to the lifetimes of the inner shell 2p3/2 hole in the Cl* (2p3/2)−1 3s23p6 configuration, and the inner shell 3d5/2 hole in the Br* (3d5/2)−1 4s24p6 configuration.

Computational Study on Protolytic Dissociation of HCl and HF in Aqueous Solution

The protolytic dissociation process of hydrochloric acid (HCl) and hydrofluoric acid (HF) is studied using the B3LYP and MP2 methods with the 6-311+G(d,p) basis set in the gas phase and in aqueous solution. To study the phenomena in detail, discrete and discrete/continuum models were applied by placing water molecules in various positions around the acid. The dissociation process was studied using the thermodynamic cycle involving the structures optimized both in the gas phase and in aqueous solution and was analyzed with two key energy factors, relaxation free energy (ΔGRex(g)) and solvation free energy (ΔGs). Based on the results, we could understand the dissociation mechanism and wish to propose the best way to study acid dissociation process using the CPCM methodology in aqueous solution.

The Entry of HCl through Soluble Surfactants on Sulfuric Acid: Effects of Chain Branching

Gas-liquid scattering experiments are used to determine how a soluble, branched surfactant (2-ethylbutanol) controls the entry of gaseous HCl molecules into 60 and 68 wt % D2SO4 at 213 K. Short-chain alcohols spontaneously segregate to the surfaces of these sulfuric acid solutions, which are representative of aerosol droplets in the lower stratosphere. We find that 2-ethylbutanol enhances HCl entry at low surface coverages, most likely because it provides extra interfacial OH groups that aid HCl dissociation. This enhancement disappears at higher coverages as the alkyl chains crowd each other and block access to the acid. The branched alcohol impedes HCl entry more effectively than its unbranched isomer 1-hexanol, implying that the larger 2-ethybutanol footprint on the surface blocks more HCl molecules from reaching the alcohol-acid interface. This behavior contrasts sharply with gas transport through long-chain monolayers, where branching introduces gaps that allow more facile passage. The experiments suggest that short-chain surfactants with extended footprints may impede transport more effectively than their unbranched isomers.

Toward predicting the mercury removal by chlorine on the ZnO surface

• HgCl 2 is directly formed by the adsorbed Cl and Hg 0 on the ZnO surface and not via HgCl intermediate. • The dissociated H atoms on the ZnO surface inhibit the formation of HgCl 2 . • Cl 2 rather than HCl is responsible for the oxidation of Hg 0 on the ZnO surface. • HgCl 2 is easy to be formed via the E–R and L–H mechanisms on the ZnO surface. The density functional theory with the generalized gradient approximation has been used to determine the binding mechanism of Cl 2 , HCl and Hg species on the ZnO( 1 0 1 ¯ 0 ) surface, and the Hg 0 oxidation mechanism by Cl 2 (or HCl) on the ZnO surface. Cl 2 and HCl are dissociatively adsorbed on the surface, and Cl atom bonds to two adjacent Zn atoms. Binding energy of Hg 0 is showing a physisorption mechanism, while HgCl 2 is strongly adsorbed on the surface in the molecularly mode, which indicates that the oxidation of Hg 0 is necessary for its removal from flue gas . HgCl is not an indispensable intermediate during the Hg 0 oxidation to form HgCl 2 . Three Hg 0 oxidation mechanisms have been investigated, and the HgCl 2 is easy to be formed via both the Eley–Rideal and Langmuir−Hinshelwood mechanisms, while Mars−Maessen mechanism is unfavorable since high activation energy is needed for Hg 0 reacting with the lattice oxygen of ZnO. The adsorbed H atoms by HCl dissociation inhibit the formation of HgCl 2 , and Cl 2 is the primary species being responsible for the Hg 0 oxidation on the ZnO surface.

Microstructural Investigation of the HCl-Induced Corrosion of the Austenitic Alloy 310S (52Fe26Cr19Ni) at 500 °C

This paper investigates the influence of 500 ppm HCl in a 5 %O2-95 %N2 atmosphere on the oxidation of the austenitic stainless steel AISI 310S at 500 °C. Laboratory exposures were made for one, 24, 72 and 168 h and the samples were analysed with XRD, SEM/EDX, FIB and TEM/EDX. When exposed in oxygen a thin and protective chromium-rich oxide scale forms. Addition of HCl causes significantly accelerated corrosion. Within the first hour of exposure, accumulations of FeCl2, CrCl2 and NiCl2 forms below the chromium-rich oxide, especially at steel grain boundaries. The chlorine-induced corrosion is suggested to occur through an electrochemical reaction, in which the dissociation of HCl to form chloride ions at the scale surface is coupled to the oxidation of the metal surface beneath the scale by an outwards electronic current and inwards diffusion of chloride ions along oxide grain boundaries

Classical simulation of acid and base dissociation constants in supercritical water at constant density

Molecular dynamics simulations were performed to investigate the dissociations of water, NaOH and HCl in water at constant density of 0.9gcm−3 at near-critical and supercritical temperatures. Results were in good qualitative agreement with available data, showing increased temperature favouring all dissociations. The dissociation of water was favoured by more negative values of U/T and an increasing entropy tem, whereas the dissociation of HCl showed both decreasing U/T and entropy. NaOH showed an increasing value of U/T which was dominated by an increasing entropy term. Differences in the energy contributions were attributed to the change in solute charges upon dissociation.

HCl Accommodation, Dissociation, and Propensity for the Surface of Water

A new reactive and polarizable molecular model was developed to describe HCl dissociation in liquid water and used to investigate HCl behavior at the air-water interface. It was found that the mechanism of HCl accommodation at the air-water interface began with its hydrogen pointing toward the water as it approached from the air. This was followed by dissociation into a contact ion pair once solvated at the air-water interface with the hydronium oriented more toward the air than the chloride on average. In comparison with NaCl, HCl showed some similar behavior in that its contact ion pair was stabilized at the air-water interface in comparison with the bulk. However, dissociated HCl had a greater propensity for the air-water interface than NaCl due to the fact that the hydronium ion was more surface active than sodium.

Dissociation of HCl into Ions on Wet Hydroxylated (0001) α-Quartz

The acidification of surfaces in the natural and built environments is important to atmospheric science because the process can enhance chemistry at surfaces and increase the release of highly reactive products into the gas phase. We present the results of an ab initio molecular dynamics study using density functional theory of HCl ionic dissociation on the hydroxylated (0001) α-quartz surface. We observed that at temperatures in the range of 250–300 K, HCl ionizes rapidly on a surface wetted with a water monolayer. It seems that ionization is enhanced by lattice mismatch between the silica and water layer. The first proton transfer to a neighboring water molecule initiates proton migration within the water adlayer via the Grotthuss mechanism. Spectroscopic signatures for the ionization are calculated and are in fair agreement with experiment.

Heterogeneous Mercury Oxidation on Au(111) from First Principles

Density functional theory (DFT) studies of mercury oxidation on Au(111) are conducted to determine the potential Hg oxidation mechanisms taking place on catalytic gold surfaces by using the Perdew and Wang approximation (PW91) described by a generalized gradient approximation (GGA). The Hg oxidation was examined via a Langmuir-Hinshelwood mechanism where each Hg(0) and Cl2 (or HCl) species is separately adsorbed on the gold surface and the bimolecular reaction occurs through the formation of bound HgCl and HgCl2. For this, the Climbing Image-Nudged Elastic Band (CI-NEB) method has been employed to calculate the activation energies of HgCl and HgCl2 formation pathways. In the three-step Hg oxidation mechanism (Hg → HgCl → HgCl2), the second Cl attachment step is endothermic which is the reaction rate-limiting step, while the first Cl attachment step is exothermic. This observation implies that Hg oxidation prefers a pathway in which HgCl and HgCl2 are formed, rather than a pathway directly oxidizing Hg to HgCl2. In the presence of H atoms due to HCl dissociation on the Au surface, the H atoms lower the activation energy for Hg oxidation by consuming the electron charge of Au atoms, thereby weakening the strength of interaction between Cl and the Au surface and lowering an energy required to detach Cl from the Au surface. This mechanism is in the absence of site competition on the Au surface. In addition, details of the electronic properties of these systems are discussed.

Selective copper diffusion into quartz-hosted vapor inclusions: Evidence from other host minerals, driving forces, and consequences for Cu–Au ore formation

Recent experimental studies have raised concerns that Cu concentrations in quartz-hosted fluid inclusions from magmatic–hydrothermal ore deposits do not represent pristine concentrations in the trapped fluids, but are modified by post-entrapment diffusional exchange through the host quartz. New microanalyses of fluid inclusions hosted in topaz show significantly lower Cu concentrations in vapor inclusions, compared to otherwise identical inclusions hosted by coexisting quartz, whereas coeval brine (hypersaline liquid) inclusions are very similar independent of host mineral in one sample. Sulfur is present as a major component in all vapor inclusions, as in most porphyry-related vapor inclusions, and Cu never exceeds S, but commonly matches the S content at a molar ratio of Cu:S⩽2 in vapor inclusions hosted by quartz.Univalent ions with a radius smaller than ∼1Å are known to diffuse rapidly through the channels of the quartz structure, parallel to its crystallographic c axis. Since only Cu concentrations differ between topaz- and quartz-hosted inclusions, we hypothesize that Cu+ and H+ re-equilibrate by diffusional ion exchange through these channels, while all other element concentrations remain essentially unchanged. A thermodynamic model considering charge-balanced Cu+H+ exchange and diffusive H2 re-equilibration of an initially Cu-poor but S-rich vapor inclusion with a typical rock-buffered fluid environment outside the host crystal demonstrates a strong chemical driving force for Cu+ to migrate from the surrounding rock into the fluid inclusion during cooling of the system. The driving force for Cu diffusion, against the gradient in total Cu concentration, is the abundant H+ liberated inside the inclusion by dissociation of HCl and particularly by the precipitation of CuFeS2 by reaction with the initially trapped H2S and/or SO2. Gold is not only a much larger ion, but is subject to an opposing driving force, suggesting that high concentrations of this larger ion analyzed in vapor inclusions probably represent true gold concentrations in magmatic–hydrothermal vapor.These findings imply that brine–vapor separation in porphyry deposits does not cause selective Cu transfer to the vapor, but is more likely to destabilize Cu complexes and promote copper ore deposition during decompression and unmixing of the two fluid phases. By contrast, Au may be selectively transferred into the vapor phase, allowing its transport through the deeper porphyry copper deposits to form epithermal gold deposits closer to the earth’s surface.

Kinetics and concentration of chlorine atoms in hydrogen chloride-argon plasma

The mechanisms of the influence of the initial composition of an HCl-Ar mixture on the kinetics and concentration of chlorine atoms in direct-current glow discharge plasma have been studied. It has been found that an increase in the Ar content at a constant total gas pressure leads to an increase in the degree of dissociation of HCl due to an increase in the electron impact dissociation efficiency.

A theoretical study of factors affecting corrosion in supercritical water reaction vessels

This paper reports a molecular dynamics study of the pKW of water, pKa of HCl and pKb of NaOH in supercritical water at a pressure of 1000atm. The extent of acid/base dissociation is known to be an important factor in the corrosion of supercritical water reaction vessels. This work describes classical molecular dynamics simulations using the SPC/e water model to gain insight into the controlling factors. The results indicate that the dissociation of water has a maximum at 448K, whereas both the dissociation of HCl and NaOH become less favourable with increasing temperature due to a decrease in entropy. The simulation results are compared to values calculated from the generalised Born theory, and there is a qualitative agreement in the trend.

Quantum control of multi-photon dissociation of HCl+ with intense femtosecond laser pulses

The multi-photon dissociation of HCl(+) through three channels HCl(+)→H(1s|(2)S)+Cl(+)((3)P), H(+)+Cl((2)P(0)), and H((2)S)+Cl(+)((1)D) steered by intense femtosecond laser pulses are investigated theoretically using the quantum wave packet dynamics. The numerical calculations are performed in two cases without and with the coupling between the excited states. The results show that the dissociation is sensitive to the duration τ, peak intensity I(0), and the resonance of driving laser fields. In the case without the coupling, the effect of the permanent dipole moments on the dissociations dominates for τ < 15 fs, while with the increase of τ, the dissociation dynamics is mainly dominated by the transition dipole moment. In the case with the coupling, the above-threshold dissociation process is complex, and the non-resonant (λ = 400 nm) and resonant (λ = 800 and 1200 nm) laser fields lead to different variation of the branching ratios. The angle-resolved energy distribution is also discussed in detail.

Calculation of the Gibbs free energy of solvation and dissociation of HCl in water via Monte Carlo simulations and continuum solvation models

The Gibbs free energy of solvation and dissociation of hydrogen chloride in water is calculated through a combined molecular simulation/quantum chemical approach at four temperatures between T = 300 and 450 K. The Gibbs free energy is first decomposed into the sum of two components: the Gibbs free energy of transfer of molecular HCl from the vapor to the aqueous liquid phase and the standard-state Gibbs free energy of acid dissociation of HCl in aqueous solution. The former quantity is calculated using Gibbs ensemble Monte Carlo simulations using either Kohn-Sham density functional theory or a molecular mechanics force field to determine the system's potential energy. The latter Gibbs free energy contribution is computed using a continuum solvation model utilizing either experimental reference data or micro-solvated clusters. The predicted combined solvation and dissociation Gibbs free energies agree very well with available experimental data.