Br2 System Research Articles

Spectroscopy learning: A machine learning method for study diatomic vibrational spectra including dissociation behavior

Molecular spectroscopy plays an important role in the study of physical and chemical phenomena at the atomic level. However, it is difficult to acquire accurate vibrational spectra directly in theory and experiment, especially these vibrational levels near the dissociation energy. In our previous study (Variational Algebraic Method), dissociation energy and low energy level data are employed to predict the ro-vibrational spectra of some diatomic system. In this work, we did the following:1) We expand the method to a more rigorous combined model-driven and data-driven machine learning approach (Spectroscopy Learning Method).2) Extracting information from a wide range of existing data can be used in this work, such as heat capacity.3) Reliable vibrational spectra and dissociation energy can be predicted by using heat capacity and the reliability of this method is verified by the ground states of CO and Br2 system.

Direct-potential-fit analysis for the [formula omitted] system of Br2

Doppler-limited rovibrational absorption spectra of the A3Π1u←X1Σg+ electronic transition of Br2 are measured in the 12072–14249cm−1 region by a tone burst modulation method using a Ti:sapphire ring laser. P-, Q-, and R-branch lines belonging to the v′←v″=(2–16)←(2–8) bands of 79,79Br2 and 79,81Br2, and the v′←v″=(2–5)←6 bands of 81,81Br2 are observed and assigned. Accurate analytic potential energy functions for the A3Π1u and X1Σg+ states are determined from a combined-isotopologue direct-potential-fit analysis of these data together with all other available high quality data for the A and X states. This work also yields a slightly improved ground-state well depth De(X)=16056.875(2)cm-1 and dissociation energy D0(X)=15894.495(2)cm-1 for 79,79Br2, and shows that the isotope shift of the A–X electronic transition energy Te81,81–Te79,79=-0.016(3)cm-1 is likely mainly due to the isotopologue dependence of theX-state well depth.

New results for the formation of a muoniated radical in the Mu + Br2 system: a van der Waals complex or evidence for vibrational bonding in Br–Mu–Br?

New evidence is presented for the observation of a muoniated radical in the Mu + Br(2) system, from μSR longitudinal field (LF) repolarisation studies in the gas phase, at Br(2) concentrations of 0.1 bar in a Br(2)/N(2) mixture at 300 K and at 10 bar total pressure. The LF repolarisation curve, up to a field of 4.5 kG, reveals two paramagnetic components, one for the Mu atom, formed promptly during the slowing-down process of the positive muon, with a known Mu hyperfine coupling constant (hfcc) of 4463 MHz, and one for a muoniated radical formed by fast Mu addition. From model fits to the Br(2)/N(2) data, the radical component is found to have an unusually high muon hfcc, assessed to be ∼3300 MHz with an overall error due to systematics expected to exceed 10%. This high muon hfcc is taken as evidence for the observation of either the Br-Mu-Br radical, and hence of vibrational bonding in this H[combining low line]-L[combining low line]-H[combining low line] system, or of a MuBr(2) van der Waals complex formed in the entrance channel. Preliminary ab initio electronic structure calculations suggest the latter is more likely but fully rigorous calculations of the effect of dynamics on the hfcc for either system have yet to be carried out.

Environmentally-Benign and Rapid Bromination of Industrially-Important Aromatics Using an Aqueous CaBr2−Br2System as an Instant and Renewable Brominating Reagent

Selective bromination of various industrially and pharmaceutically important substituted aromatics using an aqueous CaBr2−Br2 system as an instant and renewable brominating reagent is disclosed. The direct bromination of anilines and phenols with molecular bromine in solution often results in polybromination, and when brominated in the presence of oxidants, they also get oxidized rather than undergoing substitution and, in some cases, require protection of the amino (−NH2) group. We report instantaneous, facile, and regiospecific bromination of industrially important substituted anilines, phenols, aldehydes, and anilides in excellent yields and purity under ambient conditions. The byproduct HBr waste has been utilized effectively, and the brominating reagent has been rejuvenated and reused in the subsequent brominations without any significant loss of reactivity.

An instant and facile bromination of industrially-important aromatic compounds in water using recyclable CaBr2–Br2 system

Various industrially-important brominated intermediates have been instantly synthesized using aq. CaBr2–Br2 system as an efficient and recyclable brominating reagent under aqueous conditions at room temperature without the need for metal catalysts or acidic additives. Structurally-diverse phenol and aniline derivatives with strong electron-withdrawing groups such as carboxylic, nitro and formyl show remarkable reactivity to the brominating reagent and brominated in 92–98% yield with high purity (>99%) in a very short reaction time. Organic solvent-free conditions, a feature of the green chemistry, were successively used not only for the reactions but also for the isolation of products at the end of the reaction. The recycling of HBr by its neutralization, thereby generating additional amounts of industrially-important CaBr2 has been designed and developed. The brominating reagent has been recycled and regenerated, and the process was repeated up to 4 cycles after the fresh batch using the regenerated brominating reagent having almost identical selectivity and isolated yields, which seems to be the most promising methodology from the viewpoint of the green approach to organic synthesis.

Complexes of Dichloro(Ethylenediamine)Palladium(II) Observed from Aqueous Solutions by Electrospray Mass Spectrometry

Aqueous solutions of dichloro(ethylenediamine)palladium(II) were investigated using electrospray mass spectrometry (ESMS). The most abundant peak (m/z 436.8) was attributed to the dimeric Pd(en)Cl2.Pd(en)Cl+ ion. We conjecture that the structures of the observed ions arise from the clustering of the hydrolysis products of the parent compound. This hypothesis was tested experimentally by carrying out a series of collision-induced dissociation (CID) experiments and deuterium exchange reactions. It was also assessed by performing density functional theory (DFT) calculations, from which optimized structures and reaction energetics were obtained. These results were compared with our earlier ESMS study of an aqueous Pd(en)Br2 solution. Calculations were also carried out on the Pd(en)Br2 system to facilitate the comparisons. Conclusions are drawn regarding the species present in the two aqueous solutions.

Characterization of the Ground State of Br2 by Laser-Induced Fluorescence Fourier Transform Spectroscopy of the B3Π0+u–X1Σ+g System

The laser-induced fluorescence (LIF) spectrum of the B3Π0+u–X1Σ+g system of Br2 was recorded by Fourier transform spectroscopy (FTS). The LIF spectra were obtained by using continuous-wave dye laser excitation in the spectral region 16 800–18 000 cm−1. About 1800 rotationally resolved lines were recorded in 96 fluorescence progressions, originating from the 10 ≤ v′ ≤ 22 vibrational levels of the B3Π0+u state and involving the 2 ≤ v" ≤ 29 levels of the X1Σ+g ground state of the three isotopomers of bromine, 79Br2, 81Br2, and 79,81Br2. These data, together with 79Br2 data from a previous FTS absorption study [S. Gerstenkorn, P. Luc, A. Raynal, and J. Sinzelle, J. Phys. (France) 48, 1685–1696 (1987)], were analyzed to yield improved Dunham constants for the ground state. A Rydberg–Klein–Rees (RKR) potential energy curve was computed for the X1Σ+g state (v" = 0–29). The equilibrium bond length was found to be Re(X1Σ+g) = 2.2810213(20) Å.

The chain carriers of intermolecular hydrogen abstraction in the photobromination with N-bromosuccinimide; modifications of the chain carriers

The photoinitiated bromination of 1-chloropentane with N-bromosuccinimide (NBS) in the presence of Br2 is compared with that of NBS and 1,1-dichloroethene to generate the succinimidyl radical (S•) and with that of Br2 + K2CO3 to generate the bromine atom (Br•) as the chain carriers. The relative reactivities of intermolecular H-abstraction (r-values) shown by the NBS + Br2 system decrease to levels lower than those shown by either S• or Br• chain propagations at lower temperatures under appropriate conditions: these observations indicate the presence of a new chain propagating species that is assumed to be the bromine radical complex (BRC) modified from S• or Br• reversibly under the experimental conditions. Supporting evidence for the equilibria of S•, Br•, and BRC in the photodecomposition of NBS + Br2 is discussed. The unusual H-abstraction reactivity of Br• toward the methyl hydrogens of 1 -chloropentane was noted; this serves as independent support for the presence of a new radical propagation species. Keywords: N-bromosuccinimide, succinimidyl radical, photobromination, bromine radical complex.

Solvent induced vibrational population relaxation in diatomics. II. Simulation for Br2 in Ar

Results are presented from a computer simulation of the population relaxation of the lowest (1→0) vibrational transition for a system of Br2 in a dense Ar fluid at 300 K. The calculate relaxation time is 253 ps. The method of calculation is a mixed quantum–semiclassical–classical simulation procedure. The vibrational state energies and wave functions are obtained from perturbation theory for fixed values of the rotational and translational variables. The relaxation rate for the vibrational transition is evaluated using a semiclassical surface hopping theory of nonadiabatic processes. The configurations of rotational and vibrational variables are sampled from a classical canonical ensemble density using standard Monte Carlo sampling. The relative efficiency of the rotations and translations in promoting the vibrational population relaxation is examined, and the use of perturbation theory and some assumptions of the model are tested numerically.

Exchange reactions in selectively excited Br2(B3Π)

AbstractLaser‐controlled bimolecular isotopic exchange reactions in bromine leading to alterations in natural isotopic abundance ratios have been directly observed using laser‐modulated molecular beams and mass analysis. Several instances of selective excitation and subsequent rapid isotope exchange are observed within the 7 GHz gain curve of the exciting 514.5 nm line of an argon‐ion laser. These exchange processes are attributed to the direct photochemical participation of excited molecular states in the B3Πou+ system of Br2.

Laser oscillation on the 292-nm band system of Br2

Laser oscillation has been observed on numerous rotational transitions of the most intense bands of the Br2 emission system near 292 nm. The laser is electron-beam excited in an Ar-Br2 mixture. Quenching of the lower level by Br2 is inferred.

A Study of the Recoil Labeling of Fluothane with 82Br during Neutron Irradiation

Abstract 1,1,1-Trifluoro-2-chloro-2-bromoethane labeled with 82Br (fluothane-82Br) was purely separated from neutron-irradiated fluothane by means of a gas-chromatographic technique. The maximum radiochemical yield of fluothane-82Br was 38.3% when the target material was irradiated with neutrons to nvt of 3.4×1016 n·cm−2. Of the many organic species produced by the recoil events following the radiative neutron capture and subsequent (I.T.) processes, CF382Br and CF3CHBr82Br were also identified. In order to elucidate the mechanism of recoil labeling, the scavenger effects were examined in the CF3CHClBr–Br2 system, Br2 being used as a radical scavenger. The “high-energy” yields of CF3CHCl82Br thus estimated were approximately 3.6 to 4.8%. It was suggested that most of the 82Br-labeled species were formed through the “thermal” processes including the reaction of 82Br with the organic radicals produced by the radiolysis of the parent fluothane.

Further studies on the dissociation of HBr behind shock waves

AbstractPreviously reported shock tube studies of the dissociation of HBr in the temperature range of 2100–4200°K have been extended to lower temperatures (1450–2300°K) in pure HBr. The course of reaction was followed by monitoring the radiative recombination emission in the visible spectrum from Br atoms. The results imply that, in the lower range of temperatures, the activation energy of dissociation, E in the expression AT−2e−E/RT, can be approximated by the HBr bond energy (88 kcal/mole). It was also found that, in this temperature range, the rate of HBr dissociation is sensitive to the Br2 dissociation rate and the HBr + Br exchange rate. When these rates were adjusted to bring computed reaction profiles into agreement with experimental ones, it was found that the higher‐temperature data could also be fitted reasonably well with an HBr dissociation activation energy of 88 kcal/mole, contrary to the conclusions of our previous work, which favored an activation energy of 50 kcal/mole. The “best value” for k1Ar, the rate coefficient for HBr dissociation in the presence of Ar as chaperone, appears to be 1021.78 ± 0.3 T−2 10−88/θ cc/mole sec, where θ = 2.3 RT/1000; that for k1HBr, is 1022.66T−210−88/θ. A detailed review is given of the rate coefficients for the other pertinent reactions in the H2–Br2 system, viz., Br2 dissociation and reactions of HBr with H and Br.

Kinetics of the gas phase reaction of methyl benzoate with bromine and iodine: The methoxyl CH bond strength of methyl esters

AbstractThe gas phase reactions of PhCOOCH3 with I2 and Br2 were studied spectrophotometrically in a static system over the temperature ranges 344–359° and 246–303°, respectively. For each system the initial rate was first order in PhCOOCH3 and half order in halogen as the concentration of PhCOOCH3 was varied from 1.4 to 15.2 torr, that of I2 from 6.2 to 26.4 torr, and that of Br2 from 3.0 to 13.6 torr. The rate‐determining step is the extraction of a methoxyl hydrogen atom: magnified image Empirical assignment of A‐factors for k1 lead to for the I2 system, and to for the Br2 system, where ϕ = 2.303RT in kcal/mole. Combined with the assumption that E–1 = 1 ± 1 kcal/mole and 2 ± 1 kcal/mole for HI and HBr, respectively, DH (PhCOOCH2H) calculated from the two systems shows excellent agreement at 100.2 ± 1.3 kcal/mole and 100.1 ± 1.3 kcal/mole. Using a value of δH (PhCOOMe) = –65.6 ± 1.5 kcal/mole obtained from group additivity estimates, δHf,2980 (PhCOOCH2) is calculated to be –16.7 ± 2.0 kcal/mole. Unimolecular decomposition of the Ph(CO)O°CH2 radical was also observed: with a rate constant equal to The abnormally high methoxyl CH bond strength is discussed in relation to the bonding in ethers, alkanes, and esters.

Direct Interaction Theory of Reactive Molecular Collisions: K + Br2 System

Reaction cross sections and internal energy distributions are calculated quantum mechanically for the K + Br2 system. The formulation is based on some essential ideas in the Butler theory of the nuclear stripping reactions and results provide a qualitative agreement with experiment on the system.