Kr Collisions Research Articles

Energy dependence of the Penning ionization electron spectrum of Ne* (3P2,0)+Kr

A crossed beam experiment is carried out to measure the energy of electrons emitted in Penning ionization processes by Ne*(3P2,0)–Kr collisions. The electron energy spectra have been measured at four different collision energies: 0.050, 0.140, 0.190, 0.460 eV. The analysis of the results allows the separation of spin orbit contributions both in the entrance and in the exit channels providing the related cross-section ratios. Some theoretical considerations have been made to clarify nature and role of interatomic potentials driving the collisions and some general features about the role of atomic fine structure in the Penning ionization processes.

Relativistic study of vuv radiation properties from Kr-Xe gas mixtures

In an effort to obtain a microscopic understanding of the origin of vuv emission from inert heavy-atom gas mixtures we present results from relativistic calculations of the krypton-xenon spectrum in the 68 000 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ region. Calculations carried out on the interatomic interaction in the ground and in the low-lying spin-orbit excited states $[{0}^{\ensuremath{-}}{(}^{3}{P}_{2}),{0}^{+}{(}^{3}{P}_{1}),{1(}^{3}{P}_{1}),{1(}^{3}{P}_{2}),{2(}^{3}{P}_{1})]$ of the krypton-xenon dimer are presented. The calculations were executed in a two-step procedure in which the CCSD(T) model for the ground state and the CCSD response theory model for the excited states were used to obtain spin-free potential curves in the first step. A perturbational treatment of the spin-orbit interaction within the atomic mean-field approximation was applied in the next step. Large-core quasirelativistic effective core potentials with richly augmented valence basis sets and midbond functions were used. All calculations were corrected for basis set superposition errors by applying the counterpoise method. For all involved states, spin-orbit perturbed potential energy curves were computed and equilibrium geometries, potential well depths, and local extrema were determined. Vibrational analysis and Franck-Condon factors for the ground and ${0}^{+}{(}^{3}{P}_{1}{),1(}^{3}{P}_{1})$ states were also calculated. The geometry dependence of the electronic dipole transition matrix elements between all involved excited states and the ground state was investigated. Excitation energies and potentials were obtained that are in excellent agreement with results based on fitting to experimental data. Out of some earlier disparate experimental assignments of the character of the excited states of the KrXe complex, the present results adhere most closely to the ones presented by Pibel et al. [J. Chem. Phys. 101, 10 242 (1994)]. Analyzed together with the experimental data, the theoretical results provide a clear picture of the organization of exciplex states and of the origin of strong vuv emission from these states that follows from binary collisions of the heavy inert Kr and Xe atoms.

Formation of doubly charged potassium ions in K+–He and K+–Kr collisions in the 1–10 keV energy range

We present measurements of the absolute total cross-sections for the formation of K2+ ions, the production of free electrons and the excitation of K+, Ko, He and Kr particles in K+–He and K+–Kr collisions at moderate energies (1–10 keV). The formation mechanisms of K2+ ions are discussed.

Femtosecond crossed beam study of atom–atom collisions

We report femtosecond pump–probe observations of thermal Na + Kr collisions using a crossed atomic beam arrangement. Though the signal level is very small, a detectable signal is observed which shows the characteristic expected features with respect to intensity, product particle velocity, and pump–probe delay.

Multifragmentation and the phase transition: A systematic study of the multifragmentation of1AGeVAu, La, and Kr

A systematic analysis of the multifragmentation (MF) in fully reconstructed events from 1A GeV Au, La and Kr collisions with C has been performed. This data is used to provide a definitive test of the variable volume version of the statistical multifragmentation model (SMM). A single set of SMM parameters directly determined by the data and the semi-empiricalmass formula are used after the adjustable inverse level density parameter, $\epsilon_{o}$ is determined by the fragment distributions. The results from SMM for second stage multiplicity, size of the biggest fragment and the intermediate mass fragments are in excellent agreement with the data. Multifragmentation thresholds have been obtained for all three systems using SMM prior to secondary decay. The data indicate that both thermal excitation energy $E_{th}^{*}$ and the isotope ratio temperature $T_{He-DT}$ decrease with increase in system size at the critical point. The breakup temperature obtained from SMM also shows the same trend as seen in the data. The SMM model is used to study the nature of the MF phase transition. The caloric curve for Kr exhibits back-bending (finite latent heat) while the caloric curves for Au and La are consistent with a continuous phase transition (nearly zero latent heat) and the values of the critical exponents $\tau$, $\beta$ and $\gamma$, both from data and SMM, are close to those for a 'liquid-gas' system for Au and La. We conclude that the larger Coulomb expansion energy in Au and La reduces the latent heat required for MF and changes the nature of the phase transition. Thus the Coulomb energy plays a major role in nuclear MF.

Multifragmentation and the phase transition: A systematic study of the multifragmentation of 1A GeV Au, La and Kr

A systematic analysis of the multifragmentation (MF) in fully reconstructed events from 1A GeV Au, La and Kr collisions with C has been performed. Detailed comparisons of the various fragment properties are presented as a function of excitation energy, E*th. The charged particle multiplicity from MF stage shows a saturation beyond E*th ∼ 8 MeV/nucleon for Kr. The universal behavior of intermediate mass fragment yields and of the size of the largest fragment is observed only for Au and La when scaled with size of the system. The Kr data are found to lack this property. Moments of the fragment size distribution show that the Kr MF is different than the MF of Au and La. A power law behavior is observed for Au and La with exponent τ>2, while for Kr τ<2. The results are compared with the statistical multifragmentation model (SMM). A single value of all the parameters of the model fits the data for all the three systems. The breakup of Au and La is consistent with a continuous phase transition. The data indicate that both E*th and the isotope ratio temperature THc-DT decrease with increase in system size at the critical point. The breakup temperature obtained from SMM also shows the same trend as seen in data. This trend is attributed primarily to the increasing Coulomb energy with finite size effects playing a smaller role. The percolation and Ising model studies for finite size neutral matter show behavior which is opposite to the one seen in the present work.

Experimental investigation of the formation of N atoms in N+[sbnd]Ne, Kr, and Xe collisions

Total cross sections for single electron capture by N+ ions impinging on Ne, Kr, and Xe were measured in the energy range of 1.0–5.0 keV. The electron capture cross sections for all the targets studied are found to be in excellent agreement with previous data in the low-energy range. These results give a general shape of the whole curve of single electron capture cross sections for the N+Ne system over a wide range of energy. For the cases of N+Kr and N+Xe systems, semiempirical calculation using the two-state approximation are in very good agreement with present cross-section data.

Two-stage multifragmentation of1AGeV Kr, La, and Au

Multifragmentation in fully reconstructed events from 1A GeV Kr and La collisions with C has been studied. Results are compared with similar data for 1A GeV Au+C. The emitted charged particles and fragments are identified with emission from either a prompt first stage or a second stage in which the remnant resulting from the first stage breaks up. The nuclear charge, mass, and excitation energy distributions of the remnant are determined. The total charged multiplicity, as well as those of the first and second stages are obtained. Freeze-out temperatures and thermal excitation energy permit the determination of the caloric curve. The fragment charge distribution as well as the IMF multiplicity distribution and those of individual fragments are obtained. The various results are examined as to the extent of universal behavior when scaled for varying system size. Comparisons are made with intranuclear cascade and statistical multifragmentation model calculations.Received 23 February 2000DOI:https://doi.org/10.1103/PhysRevC.62.024616©2000 American Physical Society

Synthesis of silicon–nitrogen derivatives in quasi-interstellar conditions

At 2–4·10 –5 T, a silicon wafer is the target of a 5–10 keV molecular beam of dinitrogen. The products are extracted by an electric field, and analysed by mass. The ions of this primary spectrum are dissociated in a Kr collision chamber. From the fragments thus obtained, one deduces compositions for the secondary ions, and therefore for the primary products. This is helped by the presence, in silicon, of the isotopes 28 Si, 29 Si and 30 Si. Beside the clusters Si n ( n = 1–7), complex molecular species are thus obtained, such as Si 5 N 4 + , Si 5 N 4 H + , Si 5 N 4 H 2 + . © 2000 Académie des sciences / Éditions scientifiques et médicales Elsevier SAS interstellar dust / interstellar molecules / atomic impact / silicon / nitrogen derivatives Version abrégée — Synthèse de dérivés du silicium et de l'azote dans des conditions quasi interstellaires . Le bombardement d'une cible de silicium par un jet moléculaire de diazote (5–10 keV) donne des produits qui sont analysés en masse dans le domaine 0–250 u. Les ions correspondant aux pics primaires sont dissociés dans une chambre de collision (Kr, 1,5·10 –5 T). La présence, dans le silicium naturel, des trois isotopes 28,29,30 Si facilite l'interprétation de la composition de ces pics de dissociation, en permettant de ne pas confondre la présence de 28 Si avec celle de deux 14 N. La formation de diverses espèces moléculaires, telles que Si 5 N 4 + , Si 5 N 4 H + , Si 5 N 4 H 2 + , est ainsi démontrée.

A Simple Model for Ar+–Ar, He+–He, Ne+–Ne and Kr+–Kr Collisions

A simple model for ion-atom collision with charge exchange is proposed to realize a computationally efficient particle simulation of plasmas. The model is a combination of isotropic scattering and charge switching, both occurring with the same probability. When an ion-atom collision cross section is chosen to be nearly twice as large as an atom-atom collision cross section, the measured ion drift velocities and transverse diffusion coefficients for Ar+ in Ar, He+ in He, Ne+ in Ne, and Kr+ in Kr can be reproduced with reasonable accuracy using the proposed model.

Measurements of single electron capture cross sections in collisions of Kr + with Xe

Absolute differential and total cross sections for single electron capture were measured from Kr + ions on Xe in the energy range of 1.0 to 5.0 keV. The absolute total cross section shows an oscillatory behavior. The total cross section is compared with other available measurements and with a semiempirical model. The results are in good agreement with that model.

Classical and approximate quantum investigations of vibrational energy transfer in S1 p-difluorobenzene

A simple model potential energy surface is constructed and used in both quasiclassical trajectory calculations and quantum vibrational close-coupling, infinite order sudden approximation calculations of collision-induced vibrational energy transfer from four vibrational states of S1 p-difluorobenzene. Classical and quantum state-to-state cross sections are compared for excitation of the two lowest energy vibrational states and collision with He or Ar. Qualitatively, the same trends are seen in both sets of results. Classical cross sections, however, are significantly larger at very low collision energies as a consequence of the binning procedures used to determine classical final states and, in the case of the Ar collider, as a result of the possible breakdown of the sudden approximation. Rotational excitation of the p-difluorobenzene molecule is also investigated and found to have only small effects on the dominant energy transfer channels. The theoretical results are compared with recent experimental results of Mudjijono and Lawrance [J. Chem. Phys. 104, 7444 (1996)]. The classical results, for the He, Ne, Ar, and Kr collision partners, show good agreement with experiment, reproducing the major energy transfer channels and the experimental collision partner dependence. Quantum results agree well with experiment for the He collider and are also used to assign experimentally ambiguous product states and to investigate vibrational energy transfer channels that are not experimentally observable. The propensity toward the transfer of multiple quanta of vibrational energy is analyzed and, in general, found to increase with the intermolecular well depth and with the mass of the collision partner. The He collision partner, however, behaves anomalously.

Mini-EBIS report on electron capture in slow collisions of multiply charged ions with neutral targets

The status of cross section measurements carried out with a Mini-EBIS- is reported, here. Single- and multiple-electron transfer processes in collisions of Arq+ (q = 6, 7, 8, 9, and 11) with H2 and He, and those of C4+ with Ne, Ar and Kr have been investigated at low energies ranging from 0.075 eV/amu to 275 eV/amu and from 0.33 eV/amu to 667 eV/amu, respectively. All data of single-electron transfer cross sections measured for Arq+ −H2 and −He systems shows a similar tendency to converge toward the Langevin cross section at the low energy end. In the C4+ −Ne system, double-electron transfer is predominant at high energies and it is dominated by the backward scattering at low energies. From the observation of recoil ions produced in C4+ −Ar and −Kr collisions, it is found that the angular distribution of the multiple-electron transfer collisions shifts toward the backward direction in the center-of-mass frame with decreasing collision energy and four-electron transfer processes take place. The importance of the orbiting effect due to the polarization force and the backward scattering are enhanced in the single- and multiple-electron transfer collisions of highly charged ions at low energies.

Excitation transfer in collisions of Kr{4p55p; 3D3} with N2 molecules

Cross sections for the excitation of the ν1 = 0 and 1 vibrational levels of the electronically excited N2(C,ν′) product state have been measured, for collision energies in the range 85 ⩽ E(meV) </ 115, using the short-lived laser-excited Kr{(4p)55p;3D3} atoms as projectile. The cross sections Qν′ = 10.0 A2 for ν′ = 0 and 7.2 A2 for ν′ = 1 for this slightly exothermic process are interpreted in terms of a Landau-Zener model, with the ionic Kr+ + N2− state as an intermediate which crosses both the initial and final state. The crossing parameters are in good agreement with the results obtained for the similar but strongly endothermic process for the Kr{(4p)55s;3P0,3P2} + N2 systems, investigated by Vredenbregt et al. [Chem. Phys. 145 (1990) 267] in the superthermal energy range.

Target dependence of multi-electron processes in Iq+ (q=10, 15)+rare gas (Ne, Ar, Kr and Xe) collisions

We have determined experimentally the absolute cross sections for i-electron capture (to projectile) and j-electron removal (from target) ( sigma q,q-ij), total electron capture ( sigma q= Sigma i sigma q,q-i), j-electron removal ( sigma qj= Sigma i sigma q,q-ij) and i-electron capture ( sigma q,q-i= Sigma j sigma q,q-ij) for the processes: Iq+(q=10 or 15)+B to I(q-i)++Bj++(j-i)e (B identical to Ne, Ar, Kr and Xe) at collision energy of 1.5q keV. Charge-state distributions of the scattered ions were measured in coincidence with the recoil ions. The absolute electron-capture cross sections were measured by the initial growth-rate method. The experimental results for sigma q and sigma qj were compared with the predictions of the extended classical over-barrier model (ECBM). The branching ratios of the multiply-excited ions produced by multi-electron transfer have also been determined.

A crossed-beam scattering study of CH+4 and CH+3 formation in charge transfer collisions of Kr+ with CH4 at about 1 eV

The dynamics of CH+4 and CH+3 ion formation in collisions of Kr+ (2P3/2′1/2) with thermal CH4 has been investigated in a crossed beam experiment at a hyperthermal collision energy of 1.18 eV. The scattering data show that the CH+4 product is formed in a near-resonant exoergic process in which the most probable energy transferred to the target is practically equal to the recombination energy of the Kr+ projectile (resonant energy transfer); in addition a wide band of internal states of CH+4 up to ±0.6 eV is populated in inelastic and superelastic collisions. In contrast, the CH+3 product is formed in dissociative charge transfer, with about one-half of the yield due to nonresonant, endoergic collisions of Kr+ (2P3/2). The other half of the CH+3 product is found to originate in near-resonant exoergic collisions of Kr+ (2P1/2). An estimate is given of the distribution of the total energy deposited in methane by the above processes.

Absolute cross sections for the multielectron processes in 15 keV I 10+ + rare gas collisions

We have experimentally determined the absolute cross sections for total charge transfer ( σ q ), j electron transfer ( σ q j ), i electron capture ( σ q, q- i ) and each reaction process ( σ q, q- i j ) in 15 keV I 10+Ne, Ar, Kr and Xe collisions. The branching ratios were determined by the coincidence measurements between charge changing projectile and recoil ions. The electron capture cross sections were measured by the initial growth rate method. The experimental results for total and j electron transfer cross sections were compared with the predictions of the extended classical over-barrier model (ECBM).

Vacuum ultraviolet afterglow emission of rare gases and their mixtures

The results of a study of afterglow in the VUV spectral region of discharges in xenon, krypton and argon (at pressures of 0.2 to 6 Torr) are reported. Values have been obtained for recombination coefficients and formation rates of molecular ions from atomic ions, as well as for certain collisional excitation transfer constants for the 3p54s1P1 level of argon by comparing the experimental pressure dependence of resonance-line afterglow intensities with approximate analytical solutions of balance equations. The time dependence of xenon resonance lines in mixtures of helium, neon, argon and krypton were also compared with approximate solutions of the balance equations. The rate constant for the formation of xenon molecular ions in three-body collisions of Xe+ with two Xe atoms was measured to be k+(Xe)=0.8(+or-10.2)*10-31 cm6 s-1 with Ne as the third atom the same reaction had a constant of k+(Ne)=3.0(+or-0.8)*10-31 cm6 s-1 and with Ar as the third atom k+(Ar)=0.8(+or-10.2)*10-32 cm6 s-1. The Kr2+ formation constant in three-body collisions of Kr+ with two Kr atoms was measured to be 0.53(+or-0.15)*10-31 cm6 s-1 and, for Ar2+ formation in a similar reaction with two argon atoms, it is 1.9(+or-0.5)*10-31 cm6 s-1. The recombination constants alpha for the atomic ions were obtained: alpha 1(Xe)=1.5(+or-0.5)*10-9, alpha 1(Kr)=0.8(+or-0.2)*10-9, and alpha 1(Ar)=1.0(+or-10.2)*10-10 cm3 s-1.

An ion-neutral species collision model for particle simulation of glow discharge

An ion-neutral species collision model with charge exchange is developed for use in particle simulation of a glow discharge based on an extension of the theory of Langevin (1905) and Hasse (1926). The validity of the model is checked by Monte Carlo calculation of drift velocity for He+-He, Ne+-Ne, Ar+-Ar and Kr+-Kr collisions. The results show good agreement with the experimental data and the solution by the moment method, especially for heavy gases. By proper choice of the cut-off value of the dimensionless impact parameter in the model, it is applicable to a collision of ions of energy 1 keV.

Single and double electron capture in H+ on Kr collisions at low-keV energies

Abstract Absolute differential and total cross sections for single and double electron capture were measured from H + ions on krypton in the energy range of 1.0 to 5.0 keV. Both differential cross sections exhibit well-resolved oscillations over the range of angles and energies studied. Results are discussed and compared with semiempirical models and with previous measurements, showing good agreement. 1. Introduction Electron capture processes of H ÷ ions in collisions with krypton are of great importance in the fields of thermonuclear fusion research and astrophysics. Quan- titative knowledge of atomic hydrogen negative ion formation cross sections is needed for all the important atmospheric gas species [ 1 ]. The need for collisional information on the production of both neutral hydrogen and its negative ion is of current interest for neutral beam injection into fusion plasma device and in ion source development for high energy accelerators and storage rings. Most experiments concerned with the measurement of single electron capture cross sections for H ÷ [2--4] have been performed at energies below 350 eV. On the other hand few data have been accu- mulated on H+-Kr collisions in the low keV region [5-10]. Measurements of o1_1 have been reported by Williams [9] in the energy range 2.0 to 50.0 keV, by Fogel' et al. [ 11 ] at energies between 3.0 and 65.0 keV