HBr Systems Research Articles

ChemInform Abstract: Catalytic α‐Hydroxylation of Ketones under CuBr2 or HBr/DMSO Systems.

AbstractDepending on the substrate used the CuBr2 or HBr systems in DMSO deliver slightly varying yields.

THE PARTIAL POTENTIAL ENERGY SURFACE AND SCATTERING RESONANCE STATE OF THE STATE-TO-STATE REACTION Br + HBr(v) → BrH(v′) + Br

In this paper, the partial potential energy surface (PPESs) of the Br + HBr and Br - + HBr systems including the minimum energy path and the vibrational potential curves were constructed at MP2/6-311++G** level, based on the conception and constructing approach of the PPESs previously proposed. These results obtained from the PPESs were compared with those from the high resolved threshold photodetachment spectrum of the BrHBr - anion measured by Neumark et al., J Phys Chem94, 1377–1388, 1990. On the basis of the PPESs, the scattering resonance states of the Br + HBr (v) → BrH (v′) + Br state-to-state reaction were studied and the satisfactory results were obtained. Subsequently, we calculated the width and lifetime of the resonance states in this reaction by the one-dimensional square potential well model, and obtained some results consistent to the experiments.

Threshold energies for dissociative electron attachment to HBr.HX clusters with different HX partners: an ab initio study

Potential energy surfaces and threshold energies for dissociative attachment (DA) of an electron to HBr.HX clusters, viz., e - + HBr . HX → H + Br . HX - have been investigated for HX=HBr, HCl, HF and Kr by ab initio calculations at MP2 and CCSD(T) levels with large basis sets. The results show that all three hydrogen halides reduce the threshold energy to zero, while the reduction for the inert gas is much less. These results are in agreement with experimental studies, which show that capture cross sections for thermal energy electrons for the HX=HBr and HCl systems are close to the theoretical maximum. Very substantial reductions in DA threshold can be achieved by clustering, even when only one clustering partner is involved. The extent of reduction appears to depend on the initial starting geometry in the neutral dimer and other factors, as well as the magnitude of the Br −..HX binding energy.

Acidic protons before take-off: A comparative jet Fourier transform infrared study of small HCl– and HBr–solvent complexes

A comprehensive study of the proton vibrational dynamics in isolated (HX)m⋅(M)n (X=Cl, Br, and M=H2O, D2O, CH3OH) clusters is presented. Mid-IR (1900–3900 cm−1) spectra are measured in pulsed, seeded slit nozzle expansions. A close similarity among the HCl and HBr systems is revealed and exploited for cluster assignment. Distinct absorptions by small HX and mixed HX–M clusters are superimposed on broadbands, partly due to electrolytically dissociated HX in larger mixed clusters. Assignments of bands corresponding to mixed dimers and trimers based on their X–H and O–H stretching fundamentals are provided. The broad Cl–H stretching band profile of the 1:2 complex is indicative of sub-picosecond intracluster vibrational energy redistribution. The assignments are compared to matrix isolation experiments, when available. Systematic quantum chemistry calculations are performed for HCl–water complexes with up to three molecules and their isotopomers. Hydrogen bond induced frequency shifts of Cl–H stretching vibrations are best described at the coupled-cluster [CCSD(T)] level of theory. Lower level correlated quantum-chemical calculations clearly overestimate Cl–H frequency shifts. The low abundance of mixed clusters in the size range close to electrolytic dissociation (n=3–5) is discussed.

The study of interaction potentials and differential cross sections for collisions between He atoms and hydrogen halide molecules

In this paper, we present the uniform interaction potentials for helium atoms and halogen hydride molecules (HF, HCl and HBr). The differential cross sections are calculated using the above interaction potentials for the He-HF, HCl and HBr systems, respectively and the results of the calculations are found to be in agreement with the existing theoretical results and experimental data.

Extraction and separation of copper and gold from halide ion-association systems by ketones and diethyl ether

The extraction of Cu(II) and gold(III) from HCl or HBr systems was investigated. While gold was quantitatively extracted under all conditions, the extraction of copper was negligible below 1 M acidity. However, the extraction increased with increase in copper concentration to a maximum and then decreased again. In a binary mixture of the metals, the solvents exhibited such selectivity toward gold that it could be completely extracted free from copper even if the latter predominated in the mixture.

The HCl +(A 2Σ +-X 2II) and HBr +(A 2Σ +-X 2II) emissions produced by the He(2 3S), Ne( 3P 0,2)-HCl, HBr penning ionization in low-pressure flowing afterglows

Penning ionization of HCl and HBr by He(2 3S) and Ne( 3P 0,2) metastable atoms leading to HCl + (A 2Σ +) and HBr + (A 2Σ +) has been investigated spectroscopically in low-pressure He and Ne afterglows. The vibrational and rotational distributions of HCl + (A) from the Ne( 3P 0,2)-HCl system were invariant over the Ne bath pressure range of 25–800 mTorr. The vibrational distribution was shifted toward lower vibrational levels compared to the Franck-Condon distribution with rotational temperatures of 900, 550, and 350 K for υ′ = 0–2, respectively. This is explained as a consequence of a short-range final state interaction in the NeHCl + (A) → Ne + HCl + (A) process. A significant vibrational relaxation of HCl + (A) and HBr + (A) by collisions with buffer gas atoms has been found for the He(2 3S)-HCl, HBr and Ne( 3P 0,2)-HBr systems. On the basis of this fact, a discrepancy in the observed vibrational distributions in flowing affterglow and crossed beam experiments is attributed to preferential quenching of the higher vibrational levels by collisions with rare gas atoms in the former high-pressure experiment. In contrast to the significant vibrational relaxation, the produced rotational distributions (350–750 K) of HCl + (A) and HBr + (A) were independent of the rare gas pressure.

Quasiclassical trajectory studies of H(D)+HBr(DBr) abstraction and exchange reactions

Abstract The abstraction and exchange reaction dynamics for H(D)+HBr(DBr) systems have been investigated on three LEPS potential-energy surfaces whose features are in accord with the surface topography suggested by recent molecular-beam and thermal experiments (abstraction barrier less than 1.0 kcal/mole, exchange reaction barriers of =5.0 kcal/mole, and no attractive wells with a depth greater than 0.209 kcal/mole). The surfaces differ primarily in the magnitude of the abstraction barrier which varies from 0.19 to 1.01 kcal/mole. Reaction cross sections have been computed on each surface as a function of relative collision energy from the results of 139000 quasiclassical trajectoris. Comparison of these results with measured relative abstraction cross sections suggests that the true abstraction barrier is very small, perhaps between 0.0 and 0.25 kcal/mole. However, thermal rate coefficients computed on the - best- surface at 300 K are about a factor of 2 larger than the most recently measured values. The calculated (H,D)/(D,H) isotope ratio at 300 K lies between the two reported experimental results. The computed thermal activation energy for abstraction is 835 cal/mole, which is in good agreement with a very early measurements but a factor of 2.5 less than the most recently reported experimental result. These results suggest that the molecular-beam and thermal rate measurements are inconsistent. The average fraction of the available energy which is partitioned into internal product modes E > is found to be nearly independent of relative collision energy and the small topographical differences present in the potential surfaces used in these calculations. We find E > = 0.40. In all reactions, the differential scattering cross sections are peaked in the backward direction for the molecular products, indicating a rebound mechanism.

Proton affinities of hydrogen halides determined by the molecular beam photoionization method

Gas-phase proton affinities of HF (95.5±1.4 kcal/mol), HCl (135±1 kcal/mol), and HBr (141±1 kcal/mol) have been measured along with the HX+–HX binding energies for the HCl and HBr systems (20±2 and 23±2 kcal/mol, respectively) by photoionization of van der Waals molecules produced in a supersonic expansion. A detailed discussion of the potentialities and limitations of the method is presented.

Halogen hydride lasers with vibrational energy transfer from metastable diatomic molecules

The possibiliy of obtaining efficient coherent emission due to vibrational?rotational transitions in the halogen hydrides HF, DF, HCl, DCl, HBr, and DBr during vibrational energy transfer from slowly relaxing (metastable) diatomic molecules of H2, HD, D2, N2, and CO is demonstrated theoretically. It is proposed that the metastable molecules be excited by electrical preionization. A detailed analysis is made of an H2+HF+Ar system and the influence of the main factors determining the laser efficiency is identified: radiation spectrum (number of rotational sublevel J), initial gas temperature, proportions of the components, and specific energy input. An estimate is made of the opimal value of e/P (~3V?cm?1?Torr ?1). It is concluded that under optimal conditions the efficiency of these lasers may reach 40?50% for H2+HF, HD+HCl, and D2+HBr systems, and 50?70% for N2+DBr and CO+DBr systems without the active medium being cooled.

Monte Carlo quasiclassical trajectory study of Br + HBr and H + HBr: Effect of reactant vibration and rotation on reaction rates and energy transfer

A quasiclassical trajectory study of reactive and nonreactive processes in the H+HBr and Br+HBr systems is reported in which attention is focused on the role of initial internal energy on reaction rate coefficients and on angular scattering distributions and the contribution of atom-exchange reactions to vibrational energy transfer. For both systems the atom-exchange mechanism is a significant contributor to the vibrational relaxation of HBr. Initial internal excitation, either vibrational or rotational, leads to an increase in the reaction rate coefficient. In the Br+HBr case the atom-exchange product molecule is scattered in the forward direction, the distribution is insensitive to initial internal energy changes, and the trajectories are complex. On the other hand, the H+HBr reactions, abstraction and atom exchange, both proceed in a direct, uncomplicated fashion and in the case of abstraction the H2 product is scattered backward. Where possible the results are compared with other work, principally Cl+HCl.

Hot Atom Reactions in the HBr–Br2, DBr–Br2 Systems

Reactions of photochemically generated hot hydrogen atoms have been studied in HBr–Br2 systems at 185 and 229 nm and in DBr–Br2 systems at 185 nm. Kinetic analysis furnishes k3/k2—the rate coefficient ratio for the reactions H*+Br2← lim 3HBr+Brand H*+HBr← lim 2H2+Br.At 185 nm for HBr, k3/k2=4.11± 0.16, while at 229 nm k3/k2=5.48± 0.22. For DBr at 185 nm the ratio is 5.07± 0.12. Complementary trajectory calculations have been performed on a semiempirical potential-energy surface. The results of these calculations suggest that the observed variations in k3/k2 arise primarily because the reaction cross section for Process (3) varies strongly with energy in the hot atom regime and is different for the HBr and DBr systems.

Solubility behaviour of copper(I) bromide in aqueous hydrobromic acid, potassium bromide and magnesium bromide. II

AbstractThe solubility of copper(I) bromide in aqueous HBr, KBr and MgBr2 solutions has been determined at varying free bromide equilibrium concentrations. On the basis of solubility data the presence of species like CuBr2− and CuBr32− is indicated in the aqueous phase in HBr and KBr systems, whereas in the case of MgBr2 the presence of only one species, CuBr32−, is concluded. The calculated values of the equilibrium concentration constant K1 · K2 · Ksol are 3.16 × 10−1, 9.01 × 10−1 and 4.78 × 10−1 for the HBr (50°C), KBr (20°C) and MgBr2(20°C) system, respectively.

Binary gaseous diffusion coefficients of N2‐HCl, A‐HBr and N2‐HBr systems as a function of temperature

Binary gaseous diffusion coefficients of N₂‐HCl, A‐HBr and N₂‐HBr systems as a function of temperature

Chromatographic techniques using liquid anion-exchangers : II. Strong monobasic acid systems

Paper and thin-layer chromatography—which generally give analogous results—have been carried out in HNO 3, HBr, HI, HSCN and HClO 4 systems, using supports impregnated with high-molecular-weight amines and substituted ammonium salts. Based on results previously obtained in the HCl system, 5–7 liquid anion-exchangers were investigated, using approx. 10 cations for each acid system. The HBr and HI systems generally give results comparable to those found with HCl as an eluant. A more divergent picture is shown by HSCN, with which eluant it is preferable to use paper chromatography for the time being. The HNO 3 system shows fairly low adsorption for most ions, but some interesting applications are outlined. Results with HClO 4, on the other hand, are not particularly successful. The use of HI and HBr solutions containing some free I 2 and Br 2, respectively, has no unfavourable effects. The R F spectra in the HBr and HNO 3 systems show good agreement with literature data on solid anion-exchangers. Most curves may be explained assuming an anion-exchange mechanism, adsorption to the support being important incidentally. The adsorption sequence previously reported for the liquid anion-exchangers appears to be reliable for general guidance.