Br Collisions Research Articles

Theoretical and experimental studies of collision-induced electronic energy transfer from v=–3 of the E(g+) ion-pair state of Br2: Collisions with He and Ar

Collisions of Br(2), prepared in the E(0(g)+) ion-pair (IP) electronic state, with He or Ar result in electronic energy transfer to the D, D', and beta IP states. These events have been examined in experimental and theoretical investigations. Experimentally, analysis of the wavelength resolved emission spectra reveals the distribution of population in the vibrational levels of the final electronic states and the relative efficiencies of He and Ar collisions in promoting a specific electronic energy transfer channel. Theoretically, semiempirical rare gas-Br(2) potential energy surfaces and diabatic couplings are used in quantum scattering calculations of the state-to-state rate constants for electronic energy transfer and distributions of population in the final electronic state vibrational levels. Agreement between theory and experiment is excellent. Comparison of the results with those obtained for similar processes in the IP excited I(2) molecule points to the general importance of Franck-Condon effects in determining vibrational populations, although this effect is more important for He collisions than for Ar collisions.

Trajectory-dependent energy- and charge-transfer in collisions of Br +( 3P 2) with Pt( [formula omitted

Collisions of hyperthermal energy Br +( 3P 2) with Pt(1 1 1) produces scattered Br −( 1S 0) with a yield approaching 7%. The energy distribution of the scattered product exhibits an unusual dependence on the collision energy. Specifically, as the incident energy increases from 34 to 54 eV, the peak energy of scattered Br −( 1S 0) decreases. Furthermore, the anion yield reaches a sharp maximum when Br +( 3P 2) approaches the surface with 26 eV of translational energy. The unusual scattering behavior is attributed to a trajectory dependent collision-induced deformation of the lattice. The corresponding electronic perturbation evolves synchronously with the motion of the departing projectile – leading to an enhanced charge-transfer probability.

Are Semiclassical Methods Accurate for Electronically Nonadiabatic Transitions between Weakly Coupled Potential Energy Surfaces?

We have performed a systematic series of semiclassical and quantum mechanical calculations of collisions of Br* (electronicaly excited Br) with H2 in order to test four semiclassical methods against accurate quantum mechanical scattering calculations for the quenching probability and the electronically nonadiabatic reaction probability. The results are analyzed using four different methods of assigning final quantum numbers based on the final values of the semiclassical and classical trajectory variables, namely energy-nonconserving histogram analysis, energy-conserving histogram analysis, energy-nonconserving linear smooth sampling, and energy-conserving linear smooth sampling. We examine the use of both forward and reverse state-to-state probabilities to predict the quenching and reaction probabilities. The reaction and quenching probabilities are compared to the results of accurate quantum mechanical calculations, and the mean unsigned error is calculated for each combination of a semiclassical method and a final analysis algorithm. Our results indicate that Tully's fewest switches (TFS) trajectory-surface-hopping method and the Ehrenfest self-consistent-potential method show the best agreement with the accurate results, although none of the methods provides satisfactory agreement in the cases where the reaction or quenching probability is small. The TFS method is the only one that can be used to calculate the reaction probabilities for this system directly in the forward direction, and it is judged to be the best method overall for weakly coupled potential energy surfaces.

Quantum Photochemistry. The Competition between Electronically Nonadiabatic Reaction and Electronic-to-Vibrational, Rotational, Translational Energy Transfer in Br Collisions with H

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTQuantum Photochemistry. The Competition between Electronically Nonadiabatic Reaction and Electronic-to-Vibrational, Rotational, Translational Energy Transfer in Br Collisions with HSteven L. Mielke, Donald G. Truhlar, and David W. SchwenkeCite this: J. Phys. Chem. 1995, 99, 44, 16210–16216Publication Date (Print):November 1, 1995Publication History Published online1 May 2002Published inissue 1 November 1995https://doi.org/10.1021/j100044a003RIGHTS & PERMISSIONSArticle Views116Altmetric-Citations35LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (779 KB) Supporting Info (3)»Supporting Information Supporting Information Get e-Alerts

Chemiluminescence studies involving collisions of Hg+, Br+ and HgBr+ ions and HgX2 (X=Cl, Br, I) molecules

Emission spectra of the (B-X), (C-X) and (D-X) band systems of HgX radicals (X=Cl, Br, I) and mercury atomic lines from highly excited levels to various lower levels have been observed during collisions of Br+, Hg+ and HgBr+ ions and HgX2 molecules at different laboratory kinetic energies of the projectile ions. Emission cross sections of the most intense band systems and mercury atomic lines have been measured in the laboratory energy range of 100-900 eV.

Infrared fluorescence study of E–V energy transfer from Br*(4 2P1/2) to nitrosyl bromide

Electronic-to-vibration (E–V) energy transfer from excited Br(4 2P1/2) atoms to nitrosyl bromide has been investigated by an infrared fluorescence technique. The excited bromine atoms are generated by pulsed laser photolysis of Br2 at 500 nm. Approximately 50% of the quenching collisions of Br*+BrNO yield BrNO molecules excited in the 1800 cm−1 v1 stretching mode. Of these, six times as many BrNO molecules are produced in the v1=1 state as in v1=2, despite the fact that the latter is nearly resonant with the electronic energy of Br*. The total rate coefficient for removal of Br* by BrNO is determined to be (1.5±0.2)×10−11 cm3 molecule−1 s−1. Indirect comparison of our results with previous work suggests that quenching proceeds primarily by inelastic collisions; reactive quenching to form Br2+NO is probably a minor channel.

Cross sections for fast neutral-atom and positive-ion production in collisions of Br- ions with rare-gas atoms.

Atomic single-- and double--electron-detachment cross sections from ${\mathrm{Br}}^{\mathrm{\ensuremath{-}}}$ ions in He, Ne, Ar, Kr, and Xe, from 10 to 100 keV, are reported. The data fit well with other halogen-negative-ion cross sections on the same targets. There are indications that the double-detachment cross section is the same, up to about 5\ifmmode\times\else\texttimes\fi{}${10}^{5}$ cm/s, for all halogen ions on He. Above this energy, and for other beams, the cross section increases both with the beam-atom mass and with the target-atom mass. The single-detachment cross section can be fitted by the Gauyacq theory, except at the highest energies of our experiments.

Study ofδ-electron spectra produced during the collisions of Br on Pb, Br on U, and I on Pb

Differential cross sections $\frac{{d}^{2}\ensuremath{\sigma}}{d{E}_{e}d{\ensuremath{\Omega}}_{e}}$ of the $\ensuremath{\delta}$-electron emission from superheavy quasiatoms formed during heavy-ion collision of the systems Br on Pb and Br on U were measured for beam energies of 3.88 and 4.66 MeV/u. These cross sections were compared with the available theoretical results. Binding-energy differences of $K$- and $L$-shell electrons of the quasiatoms are extracted from the differential cross sections and compared with theoretical values. The measured angular distribution of $\ensuremath{\delta}$ electrons emitted from the collision system I on Pb at a beam energy of 4.0 MeV/u shows a clear isotropic behavior.

Simultaneous TOF spectra of sputtered and scattered neutrals and ions from 3 keV Ne+, Ar+, and Ar2+ bombardment of CsBr

A spectrometer system for simultaneous mass and velocity analysis of scattered and sputtered ions and velocity analysis of fast neutrals ejected from a surface by bombardment with a pulsed ion beam is described. Combination secondary ion and scattered neutral plus ion TOF spectra and their corresponding energy spectra for 3 keV Ar+ and Ar2+ bombardment of CsBr are presented. Selective sputtering of Br down to a steady state level is observed with Ne+ bombardment with an estimated depletion cross section of 10 Å2. Scattering spectra of neutrals plus ions and neutrals alone allow determination of scattered Ar+ ion survival fractions of 0.22 and 0.13 from 3 keV Ar+ collisions with Cs and Br, respectively. This indicates preferential neutralization during scattering from Br. Ion fractions for Ar2+ and Ar+ are determined for Ar2+ scattering, illustrating the stepwise neutralization process for multiply charged ions. With 3 keV Ar2+ bombardment the fractions surviving as Ar+ for Cs and Br collisions are 0.18 and 0.08, respectively, while the fraction surviving as Ar2+ is ∼0.10 for both atomic collisions. The ion fraction data are interpreted in terms of Auger and resonant neutralization transitions between the ion and specific surface atoms.

Br*(2P1/2)+H2(v=0,1): Laser studies of the competition between reactive pathways and inelastic energy transfer channels

A systematic experimental study has been made on inelastic and reactive processes in the Br*(2P1/2)+H2(v=0,1) system. Laser photolysis and time-resolved infrared detection techniques allow direct observation of the previously unreported E–V equilibrium: Br*+H2(v=0)⇄kVEkEVBr +H2(v=1). A nonlinear kinetic analysis is presented that permits an estimate of the quantum efficiencies for the forward and reverse E–V processes, and provides an explanation for previous discrepancies in measured total Br* quenching rates with H2. In this work the quenching rate constant for Br*by H2 is determined at very low Br* concentrations to be 6.3(±1)×10−12 cm3 molecule−1 sec−1. At higher concentrations of Br*, second order processes involving collisions of Br*with H2(v=1) have been investigated. A substantial fraction of the Br*+H2(v=1) collisions react to form HBr(v=0)+H(2S1/2). It is suggested that the resonant E–V transfer pathway in the entrance channel Br*+H2(v=1) → Br+H2(v=2) may provide an efficient mechanism for potential surface crossing, thereby enhancing the reaction probability.

Photofragmentation dynamics and reactive collisions of laser-excited electronic states

Tunable laser excitation followed by observation of infrared fluorescence provides a means of readily studying electronically excited photoproducts and their reactions. A number of specific examples involving the production of I*(52P1/2) and Br*(42P1/2) upon molecular photodissociation are considered. The quantum yield of I* production from HgI2 is obtained as a function of wavelength. An inconclusive search was made for unobserved states in IBr which lead to I* product atoms and for states of BrCl which lead to Br*. Photodissociation of CH2I2 in an intense laser field is observed to undergo multiphoton dissociation. Quenching and reactive collisions of Br* and I* with halogens, I2, Br2 and Cl2, and interhalogens, IBr, ICl and BrCl, are investigated. Electronically adiabatic reactive channels are detected for the collisions I*+ Br2→ IBr + Br* and I*+ IBr → I2+ Br*. Vibrationally excited HBr product molecules are observed in 10% of the quenching collisions of Br* with H2S.

Molecular-Orbital K X-Ray Formation in Heavy-Ion Collisions

In order to complete the identification of molecular-orbital $K$ x-ray spectra, we have worked out the expected spectral yields and compared them with experimental spectra produced by 30- and 60-MeV Br and 82- MeV I beams. Independently, we have determined the dominant mechanism of molecular-orbital $K$ x-ray production in 30-MeV Br + Br collisions by diluting the Br density in a solid target.

Observation ofZ=70QuasiatomicKX Rays from 30- and 60-MeVBr35+Br35Collisions

A $K$-x-ray band up to the united-atom limit for $Z=70$ has been observed in 30- and 60- MeV Br + Br collisions. This band can be assigned unambiguously to transitions between molecular orbitals. With a KBr target, yields at the two energies are (for ${E}_{x}>~22$ keV) 2 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}8}$ and ${10}^{\ensuremath{-}7}$ photons/projectile, respectively, or ${10}^{\ensuremath{-}4}$ photons/beam $K$ vacancy, nearly independent of beam energy. Much reduced yields are found for Ti, Fe, and Zr targets.

Trajectory Studies of Atomic Recombination Reactions

The radical molecule complex (RMC) theory for bromine atom recombination in the presence of an inert gas M has been tested by computing 3D classical trajectories for BrM+Br collisions. The dissociation energy of BrM was taken to be of the order of one kcal/mole. Monte Carlo methods were used to select random initial conditions of the BrM molecules with bound and metastable states included. The largest cross sections for the recombination reaction were with deep potential wells and small collision diameters for the Br–M interaction. Heavy third bodies were slightly more effective than light third bodies in promoting the reaction. The velocity averaged cross sections decreased with temperature as T−0.4 for M=Xe, T−0.6 for M=Ar and T−0.9 for M=He. Recombination rate constants, kr, were calculated at 300, 600, 1000, and 1500°K. For argon, with a Br–Ar well depth of 1.0 kcal/mole, the absolute magnitude and temperature dependence of kr agreed with experiment. For helium and xenon agreement of the calculated and experimental kr values at 300°K was obtained with the same well depth, 1.0 kcal/mole. The temperature dependence of kr was reasonable for Xe but for He the calculated value of kr at 1000°K was more than a factor of two smaller than the experimental value. The limitations of the RMC model are discussed in the light of these findings. The energy distributions for the bromine molecules formed in the recombination reaction show that the mean total internal energy is close to the dissociation energy but that there are wide spreads of rotational and vibrational energies; recombination does not take place predominantly into a few vibrational levels near the dissociation limit. The trajectory results are compared with the findings of Blake, Browne, and Burns [J. Chem. Phys. 53, 3320 (1970)] who used a Sutherland potential model for the BrM–Br interaction.