Liquid HCl Research Articles

HCl removal and recovery using choline chloride-glycerol deep eutectic solvent in rotor–stator reactor: Molecular mechanism, experimental and modeling studies

Efficient removal and recovery of HCl from off-gas are significant for environmental protection and resource utilization. In this work, the absorption process of HCl using choline chloride-glycerol (ChCl-Gly) was studied in three aspects: molecular mechanism, experimental and modeling studies. Firstly, the molecular mechanism of HCl absorption into ChCl-Gly was studied by the σ-profiles, binding models and intermolecular interaction, and it was revealed that the H atom of HCl binds with O and Cl of ChCl-Gly to form hydrogen bonds. Secondly, in view of the absorption characteristics, the process intensification of HCl absorption into ChCl-Gly was proposed by using a rotor–stator reactor (RSR). The influences of the high gravity factor, gas flowrate, ratio of gas flowrate to liquid flowrate and HCl concentration in gas inlet on the removal efficiency of HCl and overall gas-phase volumetric mass-transfer coefficient (KGa) in the removal of HCl by ChCl-Gly in the RSR were explored, and it was found that a larger high-gravity factor led to a better mass transfer effect and higher HCl removal efficiency. In addition, a mass transfer model was built to describe the process of HCl absorption into ChCl-Gly in the RSR, and the model predictions agreed well with the experimental data, and the deviations between experimental and predicted KGa were generally less than ±25 %. Finally, the prospects for industrial applications of HCl removal and recovery using deep eutectic solvents in RSR were discussed.

Safety and efficacy of a feed additive consisting of concentrated liquid l-lysine, l-lysine monohydrochloride and concentrated liquid l-lysine monohydrochloride produced by Escherichia coliNITE BP-02917 for all animal species (Metex NoovistaGo).

Following a request from the European Commission, EFSA was asked to deliver a scientific opinion on the safety and efficacy of concentrated liquid l‐lysine, l‐lysine monohydrochloride and concentrated liquid l‐lysine monohydrochloride produced by Escherichia coli NITE BP‐02917 as nutritional and as sensory (flavouring compound) feed additives for all animal species. The production strain did not carry ■■■■■ antimicrobial resistance genes and no viable cells of the production strain were detected in the final products. ■■■■■ However, since no sequences of concern remained in the production strain, the potential presence of that DNA did not raise safety concerns. The use of the three forms of l‐lysine produced by E. coli NITE BP‐02917 in supplementing feed to compensate for l‐lysine deficiency in feedingstuffs was safe for the target species. This conclusion would also cover the use as a sensory additive. The FEEDAP Panel identified risks of nutritional imbalances and hygienic concerns for amino acids when administered simultaneously in feed and in water for drinking. The use of the three forms of l‐lysine produced by E. coli NITE BP‐02917 in animal nutrition was considered safe for the consumers and for the environment. Concentrated liquid l‐lysine, l‐lysine HCl and concentrated liquid l‐lysine HCl were not considered to have the potential to cause respiratory toxicity, or skin sensitisation. l‐Lysine HCl and concentrated liquid l‐lysine HCl were not considered skin and eye irritants. Concentrated liquid l‐lysine, due to its high pH, might be corrosive for skin and eyes. The three forms were considered an efficacious source of the essential amino acid l‐lysine for non‐ruminant animal species. For the supplemental l‐lysine to be as efficacious in ruminants as in non‐ruminant species, it would require protection against degradation in the rumen. The three forms of the additive were also considered efficacious as feed flavouring compounds under the proposed conditions of use.

A Study on DSLM Transporting the Rare Earth Metal La (III) with a Carrier of PC-88A.

This paper studies transmission behavior of La (III) in dispersed supported liquid membrane (DSLM) of dispersed phase constituted by dispersed supported liquid membrane solution and HCl solution with polyvinylidene fluoride membrane (PVDF) as support and kerosene as membrane solvent, with 2-ethyl hexyl phosphonic acid-single-2-ethyl hexyl ester (PC-88A) and two-(2-ethyl hexyl) phosphoric acid (D2EHPA) as mobile carrier. It also investigates the influence of La (III) transmission by the material liquid acidity, initial concentration of La (III), HCI concentration, membrane solution, and HCI solution volume ratio, resolving agent and carrier concentration, as well as concluding that the optimal transmission and separation conditions are dispersed phase of 4.00 mol/L HCl concentration, 30:30 volume ratio of membrane solution, and HCl solution, within 0.160 mol/L controlled carrier concentration and 4.00 pH value of material liquid. Under the optimal conditions, the La (III) initial concentration of material liquid phase is 8.00 × 10–5 mol/L mol/L, 125 min, and 93.9% migration rate. Under the condition of unchanged acidity of resolving phase, HCL, H2SO4, and HNO3 as resolving agent, at 125th min, the migration rates of La (III) are 93.9%, 94.0%, and 87.8%, respectively. HCl solution, H2SO4 solution, and HNO3 solution have a certain effect on the La (III) resolution, of which 4.00 mol/L HCl solution and 2.00 mol/L H2SO4 solution are better. The effect of HNO3 is slightly lower than HCl and H2SO4.

Efficacy of different strategies to treat root dentin eroded by liquid or gaseous hydrochloric acid associated with brushing abrasion

ObjectiveThis study aims to evaluate how casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) associated with Nd:YAG or Diode laser affects dentin exposed to hydrochloric acid (HCl) with or without tooth brushing. DesignOne hundred and sixty human root dentin blocks were selected after they were initially eroded with liquid HCl (pH 1.2) 3x for one day. The blocks were divided into the following groups: G1– liquid HCl (HCl-l), G2– HCl-l + brushing, G3– gaseous HCl (HCl-g), and G4– HCl-g + brushing. Each group was randomly assigned to the following treatments (n = 10): A) Control (no treatment), B) CPP-ACP, C) CPP-ACP associated with Nd:YAG laser (λ = 1064 nm) (40 mJ, 10 Hz, 0.4 W, 15 s), and D) CPP-ACP associated with Diode laser (λ = 980 nm) (0.5 W, 200 μs, 15 s). The treatment with CPP-ACP (G2, G3 and G4) was applied on the dentine surface for 5 min. Erosion (6x/day/20 s) and erosion (6x/day/20 s) with abrasion (2x/10 s) were performed for five days. Dentin volume loss was determined by 3D confocal laser microscopy. Data were analyzed with two-way ANOVA and Tukey's tests. ResultsG1 - CPP-ACP (10.77 ± 1.66) and CPP-ACP associated with Diode laser (9.98 ± 0.89) showed lower volume loss in relation Control group (12.86 ± 0.63) (p < 0.05). G2 - CPP-ACP associated with Diode laser (12.41 ± 1.08) elicited lower volume loss as compared to the Control (14.42 ± 1.24) (p < 0.05). As for G3 and G4, all treatments showed similar volume loss. ConclusionCPP-ACP and CPP-ACP associated with Diode laser could control dental tissue loss in dentin eroded by liquid HCl. Moreover, CPP-ACP associated with Diode laser could effectively decrease dental tissue loss in dentin exposed to liquid HCl and brushing.

Chlorine isotope fractionation between chloride (Cl−) and dichlorine (Cl2)

The use of chlorine stable isotopes (35Cl and 37Cl) can help to constrain natural processes that involve chlorine species with different oxidation states. Theoretical studies based on thermodynamic and quantum mechanical approaches predict large isotope fractionation during redox reactions but to date, these reactions have not been studied experimentally.Here, we explore the chlorine isotope fractionation during the oxidation of hydrated Cl− (redox state of -I) to Cl2 (redox state of 0) at 25°C and at 0°C. Our apparatus consists of a sealed glass reactor where liquid HCl is mixed with liquid H2O2, a strong oxidant. Following complex reaction pathways, this mixture ultimately leads to the oxidation of Cl− and to the formation of Cl2 gas. As long as it is degassing, the Cl2 gas is flushed out of solution using N2 as a vector-gas from the glass-reactor to a potassium hydroxide (KOH) solution (pH 14) where it disproportionates into soluble species: Cl− and ClO−. After each experiment, the chlorine isotopic composition was measured in the recovered KOH-trap solution, as well as in the residual HCl solution. Consistent with theoretical predictions, the produced Cl2 gas is always enriched in the heavier 37Cl as compared to the initial Cl-reservoir.The following isotope fractionation factors are obtained:At 0°C the isotopic fractionation 1000lnα(Cl2−Cl−) is 4.51 (+1.65/−0.49)‰At 25°C the isotopic fractionation 1000lnα(Cl2−Cl−) is 3.94 (+0.69/−0.18)‰.From the obtained data it is suggested that the production of Cl2 gas in our experiments is best described by a closed-system distillation. Our results are in agreement with published theoretical ab-initio calculations.

Tracing chlorine sources of thermal and mineral springs along and across the Cascade Range using halogen concentrations and chlorine isotope compositions

In order to provide constraints on the sources of chlorine in spring waters associated with arc volcanism, the major/minor element concentrations and stable isotope compositions of chlorine, oxygen, and hydrogen were measured in 28 thermal and mineral springs along the Cascade Range in northwestern USA. Chloride concentrations in the springs range from 64 to 19,000 mg/L and δCl37 values range from +0.2‰ to +1.9‰ (average=+1.0±0.4‰), with no systematic variation along or across the arc, nor correlations with their presumed underlying basement lithologies. Additionally, nine geochemically well-characterized lavas from across the Mt. St. Helens/Mt. Adams region of the Cascade Range (Leeman et al., 2004, 2005) were analyzed for their halogen concentrations and Cl isotope compositions. In the arc lavas, Cl and Br concentrations from the volcanic front are higher than in lavas from the forearc and backarc. F and I concentrations progressively decrease from forearc to backarc, similar to the trend documented for B in most arcs. δCl37 values of the lavas range from −0.1 to +0.8‰ (average = +0.4±0.3‰). Our results suggest that the predominantly positive δCl37 values observed in the springs are consistent with water interaction with underlying 37Cl-enriched basalt and/or altered oceanic crust, thereby making thermal spring waters a reasonable proxy for the Cl isotope compositions of associated volcanic rocks in the Cascades. However, waters with δCl37 values >+1.0‰ also suggest additional contributions of chlorine degassed from cooling magmas due to subsurface vapor–liquid HCl fractionation in which Cl is lost to the aqueous fluid phase and 37Cl is concentrated in the ascending magmatic HCl vapor. Future work is necessary to better constrain Cl isotope behavior during volcanic degassing and fluid–rock interaction in order to improve volatile flux estimates through subduction zones.

Purification of Sn(IV) and recovery of Pd(II) from flexible printed circuit board industry wastewater via HFSLM: Temperature effect investigation

Purification of Sn(IV) and recovery of Pd(II) from flexible printed circuit board (FPCB) industry wastewater via HFSLM has been presented. This work examined the influence of extractant concentration in the liquid membrane, HCl concentration, and flow rates of feed and stripping solutions. The thermodynamic properties were also investigated. The results showed that percentage of recovery of Pd(II) was 100% and purify 84% of Sn(IV) remaining in the feed solution. The Sn(IV) and Pd(II) kinetic reaction orders approached 1.0 and the reaction rate constants were read at 0.00301 and 0.08509min−1, respectively. The experimental results were agreed with the mathematical model.

Scientific opinion on the safety and efficacy of concentrated liquid L‐lysine (base), concentrated liquid L‐lysine monohydrochloride and L‐lysine monohydrochloride produced by Escherichia coli (FERM BP‐10941) for all animal species, based on three dossiers submitted by Ajinomoto Eurolysine SAS

Concentrated liquid L-lysine (base), concentrated liquid L-lysine monohydrochloride (HCl) and L-lysine HCl technically pure are produced by fermentation with a genetically modified Escherichia coli (FERM BP-10941). Neither the production strain nor its recombinant DNA was detected in any of the final products. The final products do not raise any safety concern with regard to the genetic modifications. Concentrated liquid L-lysine (base), concentrated liquid L-lysine HCl and L-lysine HCl technically pure are considered safe for target species when supplemented in appropriate amounts. Lysine produced by E. coli (FERM BP-10941) is not genotoxic and the results of subchronic studies do not indicate any specific concerns. As there are no lysine metabolites associated with safety concerns in the animal tissues and products, the EFSA Panel on Additives and Products or Substances used in Animal Feed (FEEDAP Panel) considers that the use of L-lysine and its hydrochloride salts in animal feed does not pose a risk for the consumer. Concentrated liquid L-lysine (base), concentrated liquid L-lysine HCl and L-lysine HCl technically pure are not considered to have the potential to cause respiratory toxicity, skin or eye irritation or skin sensitisation, but respiratory sensitisation cannot be excluded. L-Lysine is a substance naturally occurring in bacteria, plants and animals. The use of L-lysine-containing feed additives does not represent a risk to the environment. Concentrated liquid L-lysine (base), concentrated liquid L-lysine HCl and L-lysine HCl technically pure are considered equivalent in terms of L-lysine availability to the target animals. The efficacy of supplementing L-lysine and its hydrochloride salts is extensively demonstrated in the literature for mammals (except ruminants), poultry and fish, including its use in a liquid or a powder form. Therefore it does not require any further demonstration. Response in ruminants requires some degree of protection of L-lysine from ruminal degradation.

Partial Halogenation of Cyclic and Branched Perhydropentasilanes

The perhydropentasilanes (H(3)Si)(4)Si and Si(5)H(10) were chlorinated with SnCl(4) to give chlorohydropentasilanes without destruction of the Si-Si backbone. Tetrachloroneopentasilane (ClH(2)Si)(4)Si (2) was prepared in high yield from (H(3)Si)(4)Si and 3.5 equiv of SnCl(4), while Si(5)H(10) and an equimolar amount of SnCl(4) afforded a mixture of ∼60% of ClSi(5)H(9) (1) with polychlorinated cyclopentasilanes and unreacted starting material, which could not be separated by distillation. The selective monochlorination of Si(5)H(10) was achieved starting from MesSi(5)Cl(9) (3; Mes = 2,4,6-trimethylphenyl) or TBDMP-Si(5)Cl(9) (4; TBDMP = 4-tert-butyl-2,6-dimethylphenyl). 3 or 4 was successfully hydrogenated with LiAlH(4) to give MesSi(5)H(9) (6) or TBDMP-Si(5)H(9) (7), which finally gave 1 along with aryl-H and Si(5)H(10) after treatment with an excess of liquid anhydrous HCl. All compounds were characterized by standard spectroscopic techniques. For Si-H derivatives, the coupled (29)Si NMR spectra were analyzed in detail to obtain an unequivocal structural assignment. The molecular structures of 2-4 were further confirmed by X-ray crystallography.

The R3O+···H+ Hydrogen Bond: Toward a Tetracoordinate Oxadionium(2+) Ion

Oxatriquinanes are tricyclic oxonium ions which are known to possess remarkable solvolytic stability compared to simple alkyl oxonium salts. Their rigid, hemispherical structure presents an oxygen at the apex of three fused five-membered rings. While trivalent oxygen species like these have been well described in the literature, the ability of oxygen to enter into a fourth covalent bonding relationship has been visited in theory and suggested by the outcome of certain reactions conducted in superacidic media, but has never been established by the characterization of a stable, persistent R(3)OH(2+) or R(4)O(2+) ion. In this study, the nucleophilicity of the oxatriquinane oxygen was evaluated first by a series of protonation studies using the Brønsted superacid H(CHB(11)Cl(11)) both in the solid state and in liquid HCl solution. The interaction of the oxatriquinane oxygen with a bridging carbocation was also examined. A strong case could be made for the occurrence of hydrogen bonding between H(CHB(11)Cl(11)) and oxatriquinane using IR spectroscopy. Under the most forcing protonation conditions, the oxatriquinane ring is cleaved to give a bridged, dicationic, protonated tetrahydrofuran-carbenium ion.

Synthesis of Mesoporous Zirconium Organophosphonate Solid‐Acid Catalysts

AbstractMesoporous zirconium phosphonate materials with bridged organic groups in the framework were hydrothermally synthesized with 1‐hydroxyethylidene‐1,1‐diphosphonic acid as coupling molecule and cetyltrimethylammonium bromide as template. The mesostructure is wormhole‐like with a specific surface area of 702 m2/g and a uniform pore size of 3.6 nm, and the organophosphonate groups are homogeneously integrated in the network of the obtained solids. The hydroxyethylidene‐bridged mesoporous zirconium phosphonates can serve as solid‐acid catalysts for the synthesis of methyl‐2,3‐O‐isopropylidene‐β‐D‐ribofuranoside from D‐ribose and exhibit high catalytic activity with rapid reaction rate, which are comparable to the catalytic performance when liquid acid HCl or commercial ion‐exchange resin NKC‐9 is used as catalyst. Furthermore, mesoporous zirconium phosphonates show high stability with good reusability without any loss of catalytic activity after five cycles, which demonstrates their potential for industrial applications.

Vibrational Energy Relaxation in Liquid HCl and DCl via the Linearized Semiclassical Method: Electrostriction versus Quantum Delocalization

The rate constant for vibrational energy relaxation of the H-Cl stretch in liquid HCl (T = 188K, ρ = 19.671 nm(-3)) is calculated within the framework of the Landau-Teller formula. The force-force correlation function is calculated via the recently introduced force-derivative-free linearized semiclassical method [Vázquez et al. J. Phys. Chem. A2010, 114, 5682]. The calculated vibrational energy relaxation rate constant is found to be in excellent agreement with experiment, and the electrostatic force is found to contribute significantly to the high frequency component of the force-force correlation function. In contrast, the corresponding classical vibrational energy relaxation rate constant is found to be 2 orders of magnitude slower than the experimental value, and the classical force-force correlation function is found to be dominated by the Lennard-Jones forces. These observations suggest that quantum delocalization, enhanced by the light mass of hydrogen, amplifies the contribution of repulsive Coulombic forces to the force-force correlation function, thereby making electrostriction an unlikely mechanism for vibrational energy relaxation in the case of hydrogen stretches. This interpretation is reinforced by the results of a similar calculation in the case of the D-Cl stretch in liquid DCl under the same conditions. In this case, the quantum enhancement of the vibrational energy relaxation rate constant is observed to be greatly diminished in comparison to HCl, thereby giving rise to a reversal of the isotope effect in comparison to that predicted by the corresponding classical treatment (i.e., whereas the classical vibrational energy relaxation rate of DCl is faster than that of HCl, the opposite trend is predicted by the linearized semiclassical treatment). It is also shown that the vibrational energy relaxation of DCl is completely dominated by the Lennard-Jones forces within either classical and semiclassical treatments, thereby suggesting that electrostriction is the underlying mechanism in this case.

Degradation of PVC Containing Mixtures in the Presence of HCl Fixators

Degradation of a model polymer mixture (PVC/PS/PE) and a waste polymer mixture in the presence of HCl fixators (Red Mud, precipitated CaCO3 and dolamite) was studied using thermal gravimetric analysis (TGA) and a cycled-spheres-reactor. The experiments in cycled-spheres reactor model were performed by stepwise pyrolysis. Liquid products and HCl from each step were collected separately. For the model polymer mixture, the precipitated CaCO3 showed the best effect on the fixation of evolved HCl and the reduction of chlorine content in the liquid products whereas RM yielded the best result for the waste polymer mixture. In addition, using HCl fixator also affected the degradation of both types of polymer mixture, leading to the formation of more gaseous and less residue.

Dielectric susceptibility of dipolar molecular liquids by ab initio molecular dynamics: application to liquid HCl

We study the dielectric susceptibility of liquid hydrogen chloride at a temperature of 313 K using ab initio molecular dynamics evolving in a homogeneous electric field. For an evolution in absence of electric field, the calculated neutron structure factor shows good agreement with the experimental one, supporting the structural properties of our model. We obtain the real and imaginary parts of the dielectric susceptibility as a function of frequency from the evolution of the polarization upon the onset of an electric field. Our simulations give a static dielectric constant of 3.65, in good agreement with the measured value of 3.8.

Collective dynamics of liquid HCl: The density–density and longitudinal current correlations

In this work the dynamics of density fluctuations in liquid HCl is investigated by computer simulation experiments, with the main goal of ascertaining the influence of hydrogen bonding in the features of the collective excitations of this molecular fluid. The data analysis shows that in HCl the hydrogen bonding has quite a small relevance on the dynamics, in strong contrast with the findings reported for both HF and water. Within the framework of generalized hydrodynamics we have been able to derive values for otherwise unknown quantities like the ratio of specific heats and the adiabatic sound velocity. An evaluation of the average effective interaction potential between the molecular centers of mass, clarifies the interpretation of the collective dynamical behavior explored in the present investigation.

Esterification of different acids over heterogeneous and homogeneous catalysts and correlation with the Taft equation

Esterification of acetic, propanoic and pentanoic acid with methanol, ethanol, 1-propanol, 2-propanol, butanol and 2-butanol was studied in the presence of a fibrous polymer-supported sulphonic acid catalyst, Smopex-101. The reaction temperature in the experiments was 60 °C. Comparative experiments were carried out on an ion-exchange resin, Amberlyst 15 and with a homogeneous catalyst, liquid HCl. The effect of different molar ratios between the reactants (acid and alcohol) on the reaction rate was investigated. The rate constants were related to the substituent effects of the reacting molecules according to the Taft equation. The substituent effects of alcohols were found to follow the Taft relationship, which was not the case for the acids. The experimental results were modelled according to a simple second-order model and a more advanced adsorption-based model. The adsorption-based model, which includes the adsorption of carboxylic acid and water and is consistent with structure–activity relationship, was superior to the second-order model.

Kinetic model for reaction of ClONO2 with H2O and HCl and HOCl with HCl in sulfuric acid solutions

The heterogeneous reactions ClONO2 + H2O → HOCl + HNO3 (1), ClONO2 + HCl → Cl2 + HNO3 (2), and HOCl + HCl → Cl2 + H2O (3) on stratospheric aerosols convert ClONO2 and HCl to photo‐labile species, producing reactive Cl and ClO which are responsible for catalyzing ozone destruction in the lower stratosphere. The extent of the resulting ozone loss mirrors the steep negative temperature dependence of these reactions, which strongly depend on the solubility of ClONO2, HCl, and HOCl, and on the activity of H2O. Predicting the effect of these heterogeneous processes throughout the stratosphere requires detailed modeling of liquid phase solubility, diffusion, and reaction kinetics. A series of recent experiments from a number of laboratories have refined measurements of liquid diffusion coefficients, HCl and HOCl solubilities, and the reactivity of ClONO2 + H2O, ClONO2 + HCl and HCl + HOCl on liquid films, droplets, and aerosols. On the basis of those measurements we present a phenomenological uptake model in which parameterizations of ClONO2, HCl, and HOCl heterogeneous kinetics appropriate for stratospheric H2SO4/H2O aerosols are addressed. In this model we suggest that under high acid concentration conditions both HOCl and ClONO2 are protonated before they react with HCl. Data for all three reactions in concentrated H2SO4 solution indicate an acid‐catalyzed reaction channel, which had previously been inferred for ClONO2 hydrolysis. This updated parameterization is most significant at relatively high temperatures above 205 K which produce H2SO4 aerosols of &gt;60 acid wt%, where the acid‐catalyzed reaction channels dominate. The comparisons between our new formulation and other recent formulations are presented.

Investigation on the mechanism and applications of the reaction Cl2+2HBr=2HCl+Br2

The mechanism of reaction Cl2+2HBr=2HCl+Br2 has been carefully investigated with density functional theory (DFT) at B3LYP/6-311G** level. A series of three-centred and four-centred transition states have been obtained. The activation energy (138.96 and 147.24 kJ/mol, respectively) of two bimolecular elementary reactions Cl2+HBr→HCl+BrCl and BrCl+HBr→HCl+Br2 is smaller than the dissociation energy of Cl2, HBr and BrCl, indicating that it is favorable for the title reaction occurring in the bimolecular form. The reaction has been applied to the chemical engineering process of recycling Br2 from HBr. Gaseous Cl2 directly reacts with HBr gas, which produces gaseous mixtures containing Br2, and liquid Br2 and HCl are obtained by cooling the mixtures and further separated by absorption with CCl4. The recovery percentage of Br2 is more than 96%, and the Cl2 remaining in liquid Br2 is less than 3.0%. The paper provides a good example of solving the difficult problem in chemical engineering with basic theory.

Orientational correlation in liquid hydrogen halides: The special case of HCl

Abstract Neutron diffraction experiments with isotopic H/D substitution from liquid HCl, HBr and HI are comparatively discussed. The hydrogen-hydrogen and halide-hydrogen radial distribution functions suggest the presence of hydrogen bonding and marked orientational correlations only in the case of HCl. Little correlations are found for HI and HBr. An analysis of the molecular configurations compatible with the experimental data from HCl, generated via a Empirical Potential Monte Carlo Simulation, allows to discuss the extent of hydrogen bonding and electrostatic forces in this system.

First spectroscopic evidence for molecular HCl on a liquid surface with sum frequency generation

Sum frequency generation spectroscopy has been used to obtain the vibrational spectrum of HCl on the surface of a liquid. HCl was studied on the surface of 96 wt % H2SO4, 12 M HCl solution, liquid HCl and glass, of which only liquid HCl produces a resonant signal. Implications for the form of HCl on surfaces and the reactions in the atmosphere are discussed.