Ionization Of HCl Research Articles

Ionization of hydrogen chloride in few-cycle intense laser pulses

The single ionization of HCl (X1Σ+) molecules in few-cycle intense laser pulses at 800 nm has been studied for laser intensities ranging from 2 × 1013 to 1.4 × 1014 W/cm2. Total and partial ionization probabilities were computed in the framework of the time-dependent Hartree-Fock theory. The influence of the laser pulse duration and the carrier envelope phase on the HCl ionization was investigated.

Triple ionization of HCl via states with a 2p core hole.

The triple ionization of HCl by double Auger decay and related processes has been studied using a multiparticle coincidence technique combined with synchrotron radiation. Four contributing processes are identified; direct double Auger, two indirect double Auger decay pathways, and single Auger decay from core-valence doubly ionized intermediate states. One indirect Auger process involves autoionization from superexcited states of Cl+. Double Auger decay from HCl+ (2p-1, 2PJ), which makes up 11% ± 2% of total Auger decay, is estimated to be 40% direct, 15% indirect via atomic Cl+* and 45% indirect via molecular intermediate doubly ionized states. The vertical triple ionization energy of HCl is determined as 73.8 ± 0.5 eV. Molecular field effects are found to affect the direct double Auger process as well as normal single Auger decay. A comparison between spectra of the HCl and DCl isotopomers indicates that electronic decay is faster in all the processes than molecular dissociation.

Computational studies of atmospherically-relevant chemical reactions in water clusters and on liquid water and ice surfaces.

CONSPECTUS: Reactions on water and ice surfaces and in other aqueous media are ubiquitous in the atmosphere, but the microscopic mechanisms of most of these processes are as yet unknown. This Account examines recent progress in atomistic simulations of such reactions and the insights provided into mechanisms and interpretation of experiments. Illustrative examples are discussed. The main computational approaches employed are classical trajectory simulations using interaction potentials derived from quantum chemical methods. This comprises both ab initio molecular dynamics (AIMD) and semiempirical molecular dynamics (SEMD), the latter referring to semiempirical quantum chemical methods. Presented examples are as follows: (i) Reaction of the (NO(+))(NO3(-)) ion pair with a water cluster to produce the atmospherically important HONO and HNO3. The simulations show that a cluster with four water molecules describes the reaction. This provides a hydrogen-bonding network supporting the transition state. The reaction is triggered by thermal structural fluctuations, and ultrafast changes in atomic partial charges play a key role. This is an example where a reaction in a small cluster can provide a model for a corresponding bulk process. The results support the proposed mechanism for production of HONO by hydrolysis of NO2 (N2O4). (ii) The reactions of gaseous HCl with N2O4 and N2O5 on liquid water surfaces. Ionization of HCl at the water/air interface is followed by nucleophilic attack of Cl(-) on N2O4 or N2O5. Both reactions proceed by an SN2 mechanism. The products are ClNO and ClNO2, precursors of atmospheric atomic chlorine. Because this mechanism cannot result from a cluster too small for HCl ionization, an extended water film model was simulated. The results explain ClNO formation experiments. Predicted ClNO2 formation is less efficient. (iii) Ionization of acids at ice surfaces. No ionization is found on ideal crystalline surfaces, but the process is efficient on isolated defects where it involves formation of H3O(+)-acid anion contact ion pairs. This behavior is found in simulations of a model of the ice quasi-liquid layer corresponding to large defect concentrations in crystalline ice. The results are in accord with experiments. (iv) Ionization of acids on wet quartz. A monolayer of water on hydroxylated silica is ordered even at room temperature, but the surface lattice constant differs significantly from that of crystalline ice. The ionization processes of HCl and H2SO4 are of high yield and occur in a few picoseconds. The results are in accord with experimental spectroscopy. (v) Photochemical reactions on water and ice. These simulations require excited state quantum chemical methods. The electronic absorption spectrum of methyl hydroperoxide adsorbed on a large ice cluster is strongly blue-shifted relative to the isolated molecule. The measured and calculated adsorption band low-frequency tails are in agreement. A simple model of photodynamics assumes prompt electronic relaxation of the excited peroxide due to the ice surface. SEMD simulations support this, with the important finding that the photochemistry takes place mainly on the ground state. In conclusion, dynamics simulations using quantum chemical potentials are a useful tool in atmospheric chemistry of water media, capable of comparison with experiment.

Experimental and theoretical investigations of energy transfer and hydrogen-bond breaking in small water and HCl clusters.

Water is one of the most pervasive molecules on earth and other planetary bodies; it is the molecule that is searched for as the presumptive precursor to extraterrestrial life. It is also the paradigm substance illustrating ubiquitous hydrogen bonding (H-bonding) in the gas phase, liquids, crystals, and amorphous solids. Moreover, H-bonding with other molecules and between different molecules is of the utmost importance in chemistry and biology. It is no wonder, then, that for nearly a century theoreticians and experimentalists have tried to understand all aspects of H-bonding and its influence on reactivity. It is somewhat surprising, therefore, that several fundamental aspects of H-bonding that are particularly important for benchmarking theoretical models have remained unexplored experimentally. For example, even the binding strength between two gas-phase water molecules has never been determined with sufficient accuracy for comparison with high-level electronic structure calculations. Likewise, the effect of cooperativity (nonadditivity) in small H-bonded networks is not known with sufficient accuracy. An even greater challenge for both theory and experiment is the description of the dissociation dynamics of H-bonded small clusters upon acquiring vibrational excitation. This is because of the long lifetimes of many clusters, which requires running classical trajectories for many nanoseconds to achieve dissociation. In this Account, we describe recent progress and ongoing research that demonstrates how the combined and complementary efforts of theory and experiment are enlisted to determine bond dissociation energies (D0) of small dimers and cyclic trimers of water and HCl with unprecedented accuracy, describe dissociation dynamics, and assess the effects of cooperativity. The experimental techniques rely on IR excitation of H-bonded X-H stretch vibrations, measuring velocity distributions of fragments in specific rovibrational states, and determining product state distributions at the pair-correlation level. The theoretical methods are based on high-level ab initio potential energy surfaces used in quantum and classical dynamical calculations. We achieve excellent agreement on D0 between theory and experiments for all of the clusters that we have compared, as well as for cooperativity in ring trimers of water and HCl. We also show that both the long-range and the repulsive parts of the potential must be involved in bond breaking. We explain why H-bonds are so resilient and hard to break, and we propose that a common motif in the breaking of cyclic trimers is the opening of the ring following transfer of one quantum of stretch excitation to form open-chain structures that are weakly bound. However, it still takes many vibrational periods to release one monomer fragment from the open-chain structures. Our success with water and HCl dimers and trimers led us to embark on a more ambitious project: studies of mixed water and HCl small clusters. These clusters eventually lead to ionization of HCl and serve as prototypes of acid dissociation in water. Measurements and calculations of such ionizations are yet to be achieved, and we are now characterizing these systems by adding monomers one at a time. We describe our completed work on the HCl-H2O dimer and mention our recent theoretical results on larger mixed clusters.

Reply to the ‘Comment on “HCl adsorption on ice at low temperature: a combined X-ray absorption, photoemission and infrared study”’ by J. P. Devlin and H. Kang, Phys. Chem. Chem. Phys., 2012,14, DOI: 10.1039/c1cp22007a

In their Comment, Devlin and Kang (DK) reinterpret the infrared data published in our previous article (P. Parent, J. Lasne, G. Marcotte and C. Laffon, Phys. Chem. Chem. Phys., 2011, 13, 7142), which look similar to those already published by V. Buch, J. Sadlej, N. Aytemiz-Uras and J. P. Devlin, J. Phys. Chem. A, 2002, 106, 9374 and J. P. Devlin, N. Uras, J. Sadlej and V. Buch, Nature, 2002, 417, 269, using assignments based on their previous model calculations (V. Buch, J. Sadlej, N. Aytemiz-Uras and J. P. Devlin, J. Phys. Chem. A, 2002, 106, 9374), with which we partially agree. However, some parts of their infrared interpretation are inconsistent with our NEXAFS and photoemission results, and they allege that these spectroscopies suffer from systematic errors due to radiation damage, which causes the fragmentation and ionization of HCl in the form of Cl−. In this Reply, we show that this assumption, central to the DK criticism, must be rejected. Furthermore, new infrared experiments confirm that, under our conditions, the band at 1740 cm−1 can be only attributed to H3O+. Then, the ionization of HCl at low temperature on H2O ice films is a mere chemical process. This leaves the whole experiment and conclusions presented in our previous article unchanged.

Two-dimensional (2+n) resonance enhanced multiphoton ionization of HCl: State interactions and photorupture channels via low-energy triplet Rydberg states

Mass spectra were recorded for (2+n) resonance enhanced multiphoton ionization (REMPI) of HCl as a function of resonance excitation energy in the 81,710-82,870 cm(-1) region to obtain two-dimensional REMPI data. Small but significant fragmentations and H(+), Cl(+), as well as HCl(+) formations are found to occur after resonance excitations to the triplet Rydberg states f (3)Delta(2)(v(') = 0), f (3)Delta(1)(v(') = 0), and g (3)Sigma(+)(1)(v(') = 0). Whereas insignificant rotational line shifts could be observed, alterations in relative ion signal intensities, due to perturbations, clearly could be seen, making such data ideal for detecting and analyzing weak state interactions. Model analysis of relative ion signal intensities, taking account of the major ion formation channels following excitations to Rydberg states, its near-resonance interactions with ion-pair states as well as dissociations and/or photodissociations were performed. These allowed verification of the existence of all these major channels as well as quantifications of the relative weights of the channels and estimates of state interaction strengths. The proposed mechanisms were supported by ion signal power dependence studies.

Microsolvation of HCl within Cold NH3 Clusters

The solid state solvation of HCl molecules with small ammonia clusters at an average temperature of 100 K was investigated by on-the-fly molecular dynamics methodology. Structures close to the proton jump from HCl molecule to the ammonia have been further checked with the MP2/aug-cc-pvDZ calculations. Ionization of HCl and/or sharing of the proton were found. Two Zundel-type ions were observedone with proton being shared between ammonium ion and Cl (-) anion (Cl (-)...H (+)...NH 3) in all complexes, and the second, between hydrogen chloride and Cl (-) anion in the HCl...Cl (-)...NH 4 (+)...(NH 3) 2 complex. However, in contrast to methanol clusters, ammonia clusters are not good for the proton wires since once the proton moves to ammonia, it is localized on the ammonium ion units.

Mechanistic study of proton transfer and H∕D exchange in ice films at low temperatures (100–140K)

We have examined the elementary molecular processes responsible for proton transfer and HD exchange in thin ice films for the temperature range of 100-140 K. The ice films are made to have a structure of a bottom D(2)O layer and an upper H(2)O layer, with excess protons generated from HCl ionization trapped at the D(2)OH(2)O interface. The transport behavior of excess protons from the interfacial layer to the ice film surface and the progress of the HD exchange reaction in water molecules are examined with the techniques of low energy sputtering and Cs(+) reactive ion scattering. Three major processes are identified: the proton hopping relay, the hop-and-turn process, and molecular diffusion. The proton hopping relay can occur even at low temperatures (<120 K), and it transports a specific portion of embedded protons to the surface. The hop-and-turn mechanism, which involves the coupling of proton hopping and molecule reorientation, increases the proton transfer rate and causes the HD exchange of water molecules. The hop-and-turn mechanism is activated at temperatures above 125 K in the surface region. Diffusional mixing of H(2)O and D(2)O molecules additionally contributes to the HD exchange reaction at temperatures above 130 K. The hop-and-turn and molecular diffusion processes are activated at higher temperatures in the deeper region of ice films. The relative speeds of these processes are in the following order: hopping relay>hop and turn>molecule diffusion.

Adsorption of HCl on the Water Ice Surface Studied by X-ray Absorption Spectroscopy

The adsorption state of HCl at 20 and 90 K on crystalline water ice films deposited under ultrahigh vacuum at 150 K has been studied by X-ray absorption spectroscopy at the O1s K-edge and Cl2p L-edge. We show that HCl dissociates at temperatures as low as 20 K, in agreement with the prediction of a spontaneous ionization of HCl on ice. Comparison between the rate of saturation of the "dangling" hydrogen bonds and the chlorine uptake indicates that hydrogen bonding of HCl with the surface native water "dangling" groups only accounts for a small part of the ionization events (20% at 90 K). A further mechanism drives the rest of the dissociation/solvation process. We suggest that the weakening of the ice surface hydrogen-bond network after the initial HCl adsorption phase facilitates the generation of new dissociation/solvation sites, which increases the uptake capacity of ice. These results also emphasize the necessity to take into account not only a single dissociation event but its catalyzing effect on the subsequent events when modeling the uptake of hydrogen-bonding molecules on the ice surface.

The double photoionization of HCl: An ion–electron coincidence study

The double photoionization of HCl molecules by synchrotron radiation has been studied in the energy range between 30 and 50 eV. The HCl(2+) and Cl(2+) product ions have been detected by a photoelectron-photoion-coincidence technique, while the H(+)+Cl(+) formation, which follows the double ionization of HCl, has been studied by photoelectron-photoion-photoion coincidence. The photon energy threshold for the production of HCl(2+) ions has been found to be 35.4+/-0.6 eV, while for the dissociative channel leading to H(+)+Cl(+), it has been measured a threshold at 36.4+/-0.6 eV and a change in the slope of the cross-section energy dependence at 38.7+/-0.7 eV. The production of H+Cl(2+) occurs with a threshold photon energy of 42.8+/-1.1 eV. These results appear to be in a good agreement with previous data by different experimental techniques and recent theoretical calculations performed by our laboratory.

Mean Force Potential between H3O+and Cl–Ions in Molecular Water Clusters: 2. Stratospheric Conditions

The behavior of the free energy of the system was analyzed. The assumption of HCl ionization in water clusters as the most probable mechanism ensuring the observed high adsorbability of ice surface relative to HCl was confirmed. It was shown that the formation of clusters containing H3O+, Cl– ion pairs is an essentially kinetic process with the participation of natural ionization sources. The characteristic time of accumulation of ionized NCl was close (by an order of magnitude) to the seasonal changes of thermodynamic conditions in the stratosphere. A kinetic theory of this phenomenon was constructed, and estimates of the content of ionized component were made. Numerical values of the parameters of kinetic equations were calculated by the Monte Carlo method.

Scattering, Trapping, and Ionization of HCl at the Surface of Liquid Glycerol

A model for the interactions between HCl and liquid glycerol, based on the Empirical Valence Bond (EVB) approach, is developed and used to investigate by molecular dynamics computer simulations the early events following the collision of an HCl molecule with the glycerol surface. The calculated trapping probability at 2.4 and 22 kcal/mol collision energies and the fractional energy loss of scattered HCl molecules agree well with experiments. The potential of mean force for HCl in the bulk and at the glycerol surface exhibits a low barrier to the formation of the contact ion pair, suggesting the possibility of proton transfer at the interface. Trapped HCl molecules undergo rapid relaxation and solvation and begin to form contact ion pairs on the picosecond time scale, which is consistent with the low barrier to the formation of the ion pair derived from the equilibrium potential of mean force calculations.

Ionization of HCl and HF in ice: a periodic DFT study

We present the results of periodic DFT–GGA calculations on the HCl and HF ionization inside a cubic ice structure. The model considers the substitution of a water molecule by an HX molecule. The potential energy curves are drawn at fixed H–X distances. HCl dissociation inside the ice structure is a barrierless process, while HF presents a typical dissociation potential curve. The selected computational methodology is able to reproduce the experimental observations.

Cl2p, O1s PSD–NEXAFS study of the adsorption of HCl on ice: a direct experimental evidence of the HCl ionization

We have used NEXAFS and photo-stimulated desorption (PSD)–NEXAFS spectroscopy at the O1s and at the Cl2p edges to study H 2O and HCl ices, as well as the adsorption of HCl on water ice. The PSD–NEXAFS provides a clear fingerprint of the dangling OH bond at the water ice surface. We evidence the H–Cl fragmentation at the 2 p→ σ ∗ (H–Cl) excitation of condensed HCl. Last, we directly observe the ionization of HCl when adsorbed on H 2O ice, both at the surface and after diffusion in the bulk of ice.

Formation of HCl+(A2Σ+) and HBr+(A2Σ+) Resulting from He(23S) Penning Ionization of HCl and HBr

He(23S) Penning ionization of HCl and HBr leading to HCl+(A) and HBr+(A) has been studied optically by using a crossed-beam apparatus. The ratios of the vibrational population, Pv‘/P0 (v‘ = 2 and 3) of HCl+(A) and P1/P0 of HBr+(A), increase with the collision energy in the region of 120−200 meV. The rotational distributions of HCl+(A, v‘= 0) and HBr+(A, v‘= 0) can be represented by a double-Boltzmann distribution; the temperatures are 200 ± 50 and 700 ± 80 K for HCl+(A, v‘= 0) and 250 ± 50 and 1200 ± 200 K for HBr+(A) and are nearly independent of the collision energy. The bimodal rotational distributions suggest that at least two processes contribute to formation of these ions. The model potential surface calculated for He*(Li) + HCl as the entrance channel is nearly isotropic and shows a shallow well of about 20 meV, whereas the surface for He + HCl+(A) as the exit channel is anisotropic and shows a deep minimum of 250 meV in the He−H−Cl collinear direction. Dynamical effects of the anisotropic attractive structure in the exit surface are proposed to account for the observed results.

Two-Dimensional Penning Ionization Electron Spectroscopy of HCl with He*(23S) Atom

Penning ionization of HCl upon collision with metastable He*(23S) atoms was studied by two-dimensional (collision-energy/electron energy resolved) Penning ionization electron spectroscopy and by classical trajectory calculations. Collision energy resolved studies enable us to obtain important information about stereo dynamical aspects on this reaction; sideways approaches of the He* atoms on H−Cl molecular axis play a dominant role in the ionization event for producing HCl+(X 2Πi, v‘ = 0, 1), and glancing collision is one of the dominant trajectories of the He* atoms to produce HCl+(A, 2Σ+). It was also found that the formation of vibrationally excited HCl+(X 2Πi, v‘ > 1) through the unidentified HCl** Rydberg state was influenced by a strong attractive interaction, whereas the formation of the HCl** Rydberg state, dissociating to H(1s) and autoionizing Cl**(1D2 nl) atoms, was found to be affected by a repulsive interaction around the Cl end of the HCl molecule.

Ice-catalyzed ionization of hydrochloric acid.

Ionization of hydrochloric acid (HCl) on stratospheric ice particles is believed to be a key step in the depletion of stratospheric ozone. Ab initio calculations based on a model HCl-water cluster show that HCl ionization on ice surfaces is a barrierless process. Since this mechanism is rapid and produces chloride anions that are exposed to ambient stratospheric chlorine reservoir molecules, it is likely to be important for stratospheric chemistry. It complements a previously suggested mechanism where HCl forms part of the ice lattice before ionizing. The mechanism proposed here is also consistent with experimentally observed ionization of HCl on ice at low temperatures and under vacuum, where the HCl is not expected to be encapsulated in the ice lattice.

Time study of pollutants at the surface of ice at 200 K

Constrained molecular dynamics simulations are performed to determine residence and transfer times of HCl and HOCl pollutants in a thin ice film at 200 K. We calculate the lifetime of small hydrogen bonded HCl–water aggregates which can induce proton transfer and HCl ionization. It is shown that rapid nanoscale pollutant adsorption/penetration in ice could be a relevant process at the origin of the reactions leading to the chlorine production.

Ab Initio Model Study of the Mechanism of Hydrogen Chloride Ionization on Ice: Reactivity of C3O2 with Ionized HCl

This paper describes an example of quantum study for two of the most important chemical processes connected to stratospheric and tropospheric heterogeneous chemistry: acid ionization of the hydrochloric acid and the proton transfer reaction on ice surfaces. Although many studies have been devoted to the subject, the HCI ionization and the acid attack of small molecules observed adsorbed on this substrate remain largely misunderstood. The heterogeneous reaction of HCl on an ice surface, which is relevant in atmospheric and stratospheric chemistry, is discussed from a theoretical approach. A proton transfer mechanism is proposed for HCl ionization on amorphous ice surfaces leading to a solvent separated ion pair. The reactivity of ionized hydrochloric acid on carbon suboxide (C{sub 3}O{sub 2}) is studied as an example and in connection with earlier experimental work. The role of the ice environment on the structure and polarization of the suboxide molecule is elucidated and a theoretical model is proposed for the synthesis of chloroformylketene.

Hydrogen bond and cooperative effect in the reactions of HOCl with HCl on water clusters

The reactions of HOCl with HCl on water clusters have been theoretically investigated. Ab initio calculations indicate that hydrogen bond and cooperative effect play an essential role in the reactions; that the reaction barrier of HOCl with cyclic (H2O)n.HCl cluster is the least at n=3 and that the ionization of HCl and HOCl on ice surfaces may not be complete but partly at very low temperatures. Two cases a and b of the model reactions are considered for detailed analysis. On the surface of ice, the barrier energies are about 4 and 6 kcal/mol for cases a and b, respectively, at the MP2//HF/6-31G(d) level, which is close to an experimental estimation. This study suggests a similar previously reported mechanism that the heterogeneous reaction of HOCl with HCl on ice is catalyzed at the stratospheric conditions through structure catalysis and hydration that enhances ion character of species.