Recoil Energy Distributions Research Articles

Some key factors of energy distributions in the products of complex-forming elementary reactions

We review some conceptual and technical tools that help in the understanding of the global shape of energy distributions in the products of complex-forming three-atom reactions governed by long-range forces. The phase space theory (PST) of chemical reactions is simplified so as to arrive at an analytical expression of the recoil energy distribution in which two major factors of the dynamics appear explicitly. These factors are called the angularexcitation ρ1′ and the diatomicinertialcontribution ρ2′ for physical reasons that are detailed in the paper. In the case of strong angular excitations, a third quantity is shown to play a role, namely, the totalangularmomentumdependenceofthereactionprobability. We also propose a straightforward procedure for estimating the statistical energy partitioning in the context of the previous findings. In this regard, the procedure should help the experimentalist significantly in the search for some of the physical factors influencing his results.

Statistical analysis of the recoil energy distributions in the products of the unimolecular dissociations of NO 2 and C 2O

Recoil energy distributions in the products of the barrierless unimolecular dissociations NO 2 → NO+O and C 2O → C+CO are derived within the framework of phase space theory (PST) in both cases where the reactant beam is supersonic or thermalized. The strong fluctuations observed experimentally in the distributions are rationalized in terms of vibrational level spacings, angular momentum constraints and the fact that the density of states corresponding to a given rotational energy of the nascent diatomic diverges when this energy tends to zero. Up to now, these fluctuations have not been considered as being compatible with a statistical process.

Recoil tritium in 304-stainless steel: the initial distribution revisited

A new experimental determination of the initial (as-deposited) concentration profile of recoil tritons (tritium) in a thick 304-S.S. target is compared with the linear recoil profile predicted by Di Cola/Matzke (DM) theory. Satisfactory agreement is observed. In the experiment, 2.72-MeV tritons produced by the 6Li(n, α) 3H reaction in a thick Li 2CO 3 powder inject a thick 304-S.S. slab with tritium. A subsequent acid etch of the slab followed by tritium and stainless steel radioassays yield the concentration profile. Monte Carlo simulations with the SRIM code show that a non-linear profile is expected, with an increasing departure from linearity occurring as the initial triton energy decreases below 2.72 MeV. DM theory is extended to cover in a slab configuration (a) recoil concentration in both source and target with arbitrary thicknesses, and (b) probability density functions describing recoil pathlength and energy distributions in a thick source and target.

Stability of metallofullerenes following neutron capture reaction on the metal ion

The stability of 16 kinds of metallofullerenes (9 elements) was investigated against the recoil phenomena associated with the capture of neutrons by the metal atoms inside the carbon cages. The yields of the unaffected species were obtained by use of the HPLC separation method and radioactivity measurements. Recoil energy distributions of the metal atoms were calculated theoretically and the effective energy required for destruction of metallofullerenes from inside by recoiling atoms was estimated to be about 10 to 15 eV for the metallofullerenes containing lanthanide atoms.

Comment on the Possibility of Excited Recoil Energy Distributions in the Products of Complex-Forming Reactions with No Exit Barrier

ADVERTISEMENT RETURN TO ISSUEPREVCommentNEXTComment on the Possibility of Excited Recoil Energy Distributions in the Products of Complex-Forming Reactions with No Exit BarrierL. Bonnet and J. C. RayezView Author Information Laboratoire de Physicochimie Moléculaire, URA 503 Université, Bordeaux 1 and CNRS 33405 Talence Cedex, France Cite this: J. Phys. Chem. A 1998, 102, 19, 3455–3456Publication Date (Web):April 17, 1998Publication History Received7 November 1997Published online17 April 1998Published inissue 1 May 1998https://doi.org/10.1021/jp980125eCopyright © 1998 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views108Altmetric-Citations-LEARN 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 (20 KB) Get e-AlertsSUBJECTS:Chemical reactions,Collisions,Energy,Physical and chemical processes,Potential energy Get e-Alerts

State-selective photofragment imaging of iodine atoms via photodissociation of CF3I at 277 nm

The photodissociation of CF3I cooled in a supersonic molecular beam has been investigated at 277 nm by state-selective photofragment imaging. Fragmented iodine atoms of two spin–orbit states are state-selectively ionized and projected onto a two-dimensional position-sensitive detector, to obtain their speed and angular distribution. The anisotropy parameter for an excited iodine atom I*(2P1/2), β(I*), is found to be 1.83 and is consistent with a dissociation lifetime in the order of 150–350 fs from rotational correlation function. Contrary to earlier reports, the parallel-like distribution for the ground state iodine atom I(2P3/2) at this wavelength, shows a more favorable curve-crossing dissociation path (68%) from 3Q0 to 1Q1 and a less favorable direct dissociation path (32%) from 3Q1. The recoil energy distribution of I is found to be broader than that of I* and is correlated with a variety of energy disposal channels by an e symmetry vibration at the crossing point. The results are compared with previous works, and the strong photon energy dependence of the energy partitioning in CF3+I* channel and curve crossing are interpreted in terms of the final state interaction and curve crossing probability, respectively.

The classical statistical theory of three-atom reactions governed by short-range forces: Energy transfers and recoil energy distribution

When the nascent products of a three-atom reaction governed by chemical forces separate, energy transfers may occur between vibrational, rotational, and translational motions. In the first part of the paper, we show from quasiclassical trajectory calculations on a model potential energy surface that (a) the vibrational energy is adiabatic on average as usually assumed in statistical theories, (b) rotational-translational energy transfer mainly favors translational motion (as was initially suggested by Marcus), but that (c) this transfer is inefficient when the product atom is sufficiently light with respect to the other two. A qualitative analysis of these findings is proposed based on arguments differing from those of Marcus, and Quack and Troe. In the second part of the paper, we extend the classical statistical formalism proposed recently by ourselves, initially limited to reactions governed by long-range forces, to the present more general case of reactions involving tight transition states and for which energy transfers are inefficient. In such a case, energy distributions at the exit transition state and in the products are the same. We focus our developments on the recoil energy distribution. Agreement between our theoretical result and the quasiclassical trajectory approach is shown to be very satisfactory.

Main factors influencing the recoil energy distribution in the products of three-atom reactions governed by long-range forces and proceeding through long-lived complexes

We propose a simplified version of the classical statistical theory of three-atom reactions governed by long-range forces. This version is based on a partial treatment of total angular momentum conservation. We focus the developments on the determination of the recoil energy distribution of reactions performed in supersonic crossed-beam experiment. This distribution function is directly linked to the maximum values of the moduli of rotational and orbital angular momenta of the products consistent with their recoil energy and the total angular momentum disposal. Due to the simplicity of the present version, we can pinpoint the main factors which play a role in statistical reaction dynamics. It is shown that the shape of the translational energy distribution can be estimated essentially in terms of two mechanical parameters; the first one represents the available fraction of maximum angular momentum disposal in the products and the second gives a measure of the fraction of total angular momentum due to the rotation of the newly formed bond AB. Comparisons with exact calculations and experimental results are presented. They show that in addition to being able to determine propensity rules, our simple approach can even provide satisfying quantitative results.

Collision cascades in binary media: Analytical results for power-law cross sections

We study the energy distributions of recoils in a fast-ion induced collision cascade in a binary medium. Concentrating on power-law interaction cross sections — with different powers m ij for collisions between a recoil of species i and a particle of species j — we solve the forward transport equations in the asymptotic limit of small recoil energies. We find that three qualitatively different regimes of solution exist, and define their regions of validity: detailed balance, where the recoil energy distributions are determined by interspecies collisions; ignorance, where both species show an energy spectrum as if they were in a monoatomic medium; and dominance, where one species behaves as if in a monoatomic medium, while the energy distribution of the dominated species is determined by energy transfer to and from the dominant species. We present analytical expressions for the energy distributions and recoii densities in a binary medium for the different regimes. The results are checked by means of a numerical solution of the transport equations, using Monte Carlo computer simulation.

Infrared multiphoton dissociation of anisole: production and dissociation of phenoxy radical

The infrared multiphoton dissociation of anisole in a molecular beam was studied using pulsed CO 2 laser radiation, with the product recoil energy distributions measured using the time-of-flight technique. The only primary process identified was the dissociation into phenoxy and methyl radicals, with the shape of the translational energy distribution of the products revealing a small exit barrier. Under conditions of higher laser fluence, secondary dissociation of the phenoxy radical into carbon monoxide and C 5 H 5 was observed

Dynamics of the reactions of C+ with C2H6

We present a crossed beam study of the major reactive channels of C++C2H6 in the collision energy range between 0.8 and 1.6 eV. We find that C2H+5 formation proceeds as a direct hydride abstraction reaction with the accompanying CH product scattered in the forward hemisphere. The product recoil energy distribution shows a distinct Gaussian shape that we correlate with the nature of the potential energy surface for transfer of the light hydride ion between two heavy species. C2H+3 formation occurs through two pathways: the first and most important route is direct interaction of C+ with C2H6 to form a new C–C bond with the ejection of CH3 in a collinear interaction that leads to backward scattering of the ionic product. A second, and much less probable pathway involves formation of this product through a transient collision complex living a significant fraction of a rotational period. The condensation product C3H+3 is by far the most abundant C3 product observed in this collision energy range. The sideways-peaked angular distribution for its formation is consistent with a mechanism where the initially formed C3H+6 complex decays in a step in which a molecule of H2 is ejected in a direction perpendicular to the plane of rotation defined by the three carbon atoms. The kinetic energy distribution for this channel is significantly broader than the predictions of statistical phase space theory and underscores the importance of potential energy exit channel barriers in determining product recoil in such elimination processes. We discuss these results in the context of a schematic potential energy surface incorporating thermochemical data and results of ab initio calculations.

MULTIPLE CAPTURE AND IONISATION IN HIGH ENERGY ION-ATOM COLLISIONS

Multiple electron processes occuring in high energy ion-atom collisions are investigated through Independent Electron Models (IEM), some limits of which are indicated for double capture processes. It is shown that an IEM permits to exhibit non perturbative behaviours of the ionisation process. It appears to be a powerful tool to predict multiply charged recoil ion production and recoil energy distribution when the impact velocity of the primary beam is high enough.

Reactive scattering from double minimum potentials: Li+ catalyzed elimination reactions of alkyl halides

We present a study of the dehydrohalogenation reactions of Li+ with isopropyl chloride (IPC), n-propyl chloride (NPC), and isopropyl bromide (IPB) over the collision energy range from 0.6 to 1.7 eV. Full differential cross sections at collision energies up to 1.2 eV show increasing asymmetry in the angular distributions as a function of initial collision energy and suggest that the reactions take place on a time scale of 0.2 ps. The observation of Li+ nonreactively ejected from the initial encounter complex formed by approaching reactants is consistent with a double minimum reaction coordinate and a comparison of the nonreactive flux with the flux for elimination products allows an estimate of the heights of intermediate isomerization barriers separating the wells on the potential surface. The barrier heights are in the order IPC<IPB<NPC, consistent with a transition state at the isomerization barrier in which a significant charge has developed on the carbon attached to the halogen. The kinetic energy distributions for Li+(HX) and Li+(C3H6) products and nonreactively scattered Li+ are in reasonable agreement with phase space theory calculations which include all product vibrational modes. The energy dependence of the Li+(HX)/Li+(C3H6) branching ratio can be accounted for quantitatively by statistical calculations which include the increasing importance of dissociation of the products with increasing collision energy. The discrepancy between the statistical recoil energy distributions and apparent complex lifetimes several orders of magnitude shorter than the predictions of RRKM theory can be understood in terms of incomplete transfer of energy from the incident Li+ to the internal degrees of freedom of the initial encounter complex, resulting in a density of complex states much lower than statistical.

Reactive scattering from double-minimum potentials

We present a crossed-beam study of the elimination reactions of Li+ with t-butyl alcohol (TBA), isopropyl chloride (IPC), n-propyl chloride (NPC), and isopropyl bromide (IPB) over the collision energy range 0.6–2.5 eV. Full differential cross-sections at collision energies up to 1.2 eV show increasing asymmetry in the angular distributions as a function of initial collision energy and suggest that the reactions take place on a timescale of 0.2–0.5 ps. The observation of Li+ being non-reactively ejected from the initial encounter complex formed by approaching reactants is consistent with a double-minimum reaction coordinate and a comparison of the non-reactive flux with the flux for elimination products allows an estimate of the heights of intermediate isomerization barriers separating the wells on the potential surface. The kinetic energy distributions for Li+(HX) and Li+(olefin) products and non-reactively scattered Li+ are in reasonable agreement with phase-space theory calculations which include all product vibrational modes. The energy dependence of the Li+(HX)/Li+(olefin) branching ratio can be accounted for with statistical calculations which include product dissociation. The discrepancy between the statistical recoil energy distributions and apparent complex lifetimes several orders of magnitude shorter than the predictions of RRKM theory can be understood in terms of the specific dynamics of passage from the crest of the isomerization barrier to the second well of the potential surface and the apparent failure of the system to re-establish microcanonical equilibrium in that well.

Electron-positron pair production by ultrarelativistic electrons in a soft photon field

view Abstract Citations (27) References (11) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Electron-Positron Pair Production by Ultrarelativistic Electrons in a Soft Photon Field Mastichiadis, A. ; Marscher, A. P. ; Brecher, K. Abstract The fully differential cross section for photon-electron pair production is integrated numerically over phase space. Results are obtained for the astrophysically interesting case in which the interaction between an ultrarelativistic electron and a soft photon results in electron-positron pair production. The positron spectrum is a function of the energies of both the photon and the electron, as well as the angle of interaction. It is found that the energy at which the positron distribution peaks is inversely proportional to the photon energy and independent of the electron energy. The positron spectrum is integrated once more over initial electron energies for a power-law energy distribution of primary electrons. The same procedure is repeated for the recoil particle; it is shown that the peak of the recoil energy distribution depends linearly on the energy of the primary electron. Finally, semianalytical expressions are obtained for the energy losses of the primary electrons. Publication: The Astrophysical Journal Pub Date: January 1986 DOI: 10.1086/163792 Bibcode: 1986ApJ...300..178M Keywords: Computational Astrophysics; Electron-Positron Pairs; Pair Production; Photon-Electron Interaction; Relativistic Electron Beams; Electron Energy; Energy Dissipation; Energy Distribution; Gamma Rays; Positrons; Astrophysics; ELEMENTARY PARTICLES; GAMMA RAYS: GENERAL; RADIATION MECHANISMS full text sources ADS |

124Sn target residues in the interaction of heavy ions at intermediate energies

Cross sections, recoil energy distributions for residues produced by14N,20Ne,40Ar on124Sn targets have been measured in the 10–70 MeV/u intermediate energy range. As the projectile energy increases, processes as complete fusion-evaporation, incomplete fusion-evaporation and intranuclear cascade-evaporation participate progressively in the nuclear collisions. Peculiar residues corresponding to a gain of 4, 5 or even 6 protons for the124Sn target have been observed in the 30–50 MeV energy range.

Photodissociation of dibromodifluoromethane at 248 nm by the molecular beam method

The photochemistry of CF/sub 2/Br/sub 2/ at 248 nm has been studied by the crossed laser-molecular beam technique. The only primary reaction channel observed is atomic bromine elimination: CF/sub 2/Br/sub 2/ ..-->.. CF/sub 2/Br + Br. Laboratory angular and time-of-flight distributions of the CF/sub 2/Br and Br primary products were measured and used to derive the center-of-mass (CM) product recoil energy and angular distributions for this reaction. The average CM recoil energy of the products is 21.3 kcal/mol. The shape of the CM angular distribution indicates that the transition dipole moment is polarized parallel to the Br-Br direction in CF/sub 2/Br/sub 2/. The molecular bromine elimination reaction, CF/sub 2/Br/sub 2/ ..-->.. CF/sub 2/ + Br/sub 2/, does not occur to a measurable extent at 248 nm. However, CF/sub 2/ radicals are produced in abundance under collision-free conditions, due to the efficient secondary photodissociation of some of the CF/sub 2/Br primary product.

ChemInform Abstract: UNIMOLECULAR DECOMPOSITION OF NITROMETHANE IN A MOLECULAR BEAM WITH RESOLUTION OF FRAGMENT RECOIL VELOCITIES AND INTERNAL STATES: DYNAMICAL EVIDENCE FOR AN EXIT CHANNEL BARRIER

We report the application of multiphoton ionization (MPI) to a study of the dynamics of the unimolecular decomposition of nitromethane. CH3 and NO2 products from the CO2 laser‐induced infrared multiphoton dissociation of CH3NO2 in a skimmed supersonic molecular beam are detected with time, space, and quantum state resolution by resonant multiphoton ionization. An analysis of angular and time‐of‐flight distribution of products characterizes their center‐of‐mass recoil energy distribution. Spectroscopic analysis of NO2 and CH3 MPI spectra determine the distributions of rotational states populated by the decomposition. Data are interpreted within the framework of a direct count phase‐state theory approach which is used to calculate statistical distributions over product states within the constraint of explicitly conserved angular momentum. Phase‐space theory rotational state distributions fit well with experiment, but experimentally observed translational energies are nearly an order of magnitude greater tha...

Unimolecular decomposition of nitromethane in a molecular beam with resolution of fragment recoil velocities and internal states: Dynamical evidence for an exit channel barrier

We report the application of multiphoton ionization (MPI) to a study of the dynamics of the unimolecular decomposition of nitromethane. CH3 and NO2 products from the CO2 laser-induced infrared multiphoton dissociation of CH3NO2 in a skimmed supersonic molecular beam are detected with time, space, and quantum state resolution by resonant multiphoton ionization. An analysis of angular and time-of-flight distribution of products characterizes their center-of-mass recoil energy distribution. Spectroscopic analysis of NO2 and CH3 MPI spectra determine the distributions of rotational states populated by the decomposition. Data are interpreted within the framework of a direct count phase-state theory approach which is used to calculate statistical distributions over product states within the constraint of explicitly conserved angular momentum. Phase-space theory rotational state distributions fit well with experiment, but experimentally observed translational energies are nearly an order of magnitude greater than expected. We conclude that energy release associated with an exit channel barrier for C–N scission dynamically alters fragment recoil energy distributions.

Several directional effects for fast ionized recoils

Abstract Detailed dependences of the energy distributions of fast ionized recoils ejected from both single- and polycrystalline copper targets bombarded by 30 keV Ar+ ions on the geometry of the experiment have bccn investigated. The model of an isolated vibrating atomic row proves to bereasonable for describing many of the features obtained in ejected recoil energy distributions.