Product Kinetic Energy Research Articles

Analysis of ion densities in the vicinity of space vehicles: Ion‐neutral chemical kinetics

Recent laboratory studies of ion‐molecule reactions relevant to the analysis of ion densities in the vicinity of space vehicles in low‐Earth orbit are discussed. The studies include new cross‐section measurements of the important O++ H2O charge transfer collisions and the H3O+ ‐producing H2O++ H2O collisions, as well as product kinetic energy analysis of the reaction products. The charge transfer reaction rate is found to be less collision energy dependent than previously assumed, whereas the H3O+ ‐producting reaction rate is highest at thermal energies and decreases rapidly with increasing collision energy. Implications of the new results on previous interpretations and recent space observations are discussed.

Recoil properties of deep spallation and fragmentation products in the interaction of tantalum with 3.65 AGeV 12C-ions and protons

Thick-target recoil properties of deep spallation and fragmentation products of the interaction of tantalum with 3.65 AGeV 12C-ions and 3.65 GeV protons have been studied. The kinematic parameters such as mean product kinetic energies and velocities of the remnant have been deduced from the data by means of the two-step vector velocity model of high-energy reactions. The results have also been used to test the applicability of the factorization hypothesis to the kinematic properties.

ChemInform Abstract: Cross Sections and Product Kinetic Energy Analysis of H2O+‐H2O Collisions at Suprathermal Energies.

AbstractThe H2O+‐H2O reaction is studied at center‐of‐mass collision energies in the range 0.5‐25 eV.

Kinetic energy release distributions as a probe of ligation effects on potential energy surfaces in organometallic reactions. Reversible dehydrogenation of cycloalkenes by iron cation

The kinetic energy release distributions associated with dehydrogenation and double-dehydrogenation processes for Fe{sup +} reacting with cyclopentene, cyclohexene, cyclopentane, and cyclohexane have been obtained. Previously, dehydrogenation of alkanes and alkenes by Co{sup +} and Ni{sup +} in the gas phase has been characterized by release of more energy into product translation than can be accounted for by statistical theory. This observation is not general, however, since here the authors show dehydrogenations of cyclopentene and cyclohexene by Fe{sup +} are well described by statistical phase-space theory with the best fit of theory to experiment yielding D{sub 0}{sup o}(Fe{sup +}-C{sub 5}H{sub 6}) = 50 {plus minus} 5 kcal/mol and D{sub 0}{sup o}(Fe{sup +}-C{sub 6}H{sub 8}) = 66 {plus minus} 5 kcal/mol. For statistical theory to be applicable, it is required that there be no barrier for the reverse association reaction. The absence of a barrier in these systems is consistent with studies that indicate H/D exchange for Fe(C{sub 5}H{sub 6}){sup +} is reversible and occurs in the presence of excess D{sub 2} at about 5% of the Langevin collision rate. The product kinetic energy release distributions measured for the final hydrogen loss in the double dehydrogenations of cyclopentane and cyclohexane by Fe{sup more » +} are remarkably similar to those obtained for single dehydrogenations of cyclopentene and cyclohexene. This similarity is explained by participation of electronically excited Fe{sup +} in the first step of the double-dehydrogenation processes, which supplies the additional energy required to observe the second H{sub 2} loss as a metastable process. « less

Cross sections and product kinetic energy analysis of H2O+–H2O collisions at suprathermal energies

The reaction of H2O+ with H2O is studied using a longitudinal geometry double mass spectrometer in the collision energy range Ec.m.=0.5–25 eV. Cross sections are reported for oxonium ion (H3O+) production and the symmetric charge exchange. Isotopic substitution is used to discern the product branches, including the separation of the two channels for oxonium ion production: (i) proton transfer to the target molecule; and (ii) atom pickup by the primary ion. The largest branching ratio is observed for the charge exchange channel, where no isotope effect is detected in the investigated energy range. Proton transfer exhibits the second largest branching ratio and accounts for more than 90% of the oxonium ion production throughout the measured energy range. The proton transfer cross section is dependent on isotopic substitution, while the atom pickup channel is too weak to make a distinct statement on its isotopic behavior. Product ion energies, determined by time-of-flight measurements, are also reported for each of the three channels. These measurements show that most (>95%) of the oxonium ions are formed via a direct, spectator stripping type mechanism while a small amount of reaction products exhibit considerable internal excitation. The charge exchange secondary ions are primarily formed at near-thermal energies in the laboratory frame. Small amounts of high laboratory energy product ions are also observed which at least partly originate through the dissociation of excited oxonium ions.

Photodissociation of CO−3: Product kinetic energy measurements as a probe of excited state potential surfaces and dissociation dynamics

The photodissociation process CO−3 +hν→O−+CO2 has been investigated at photon energies of 2.41, 2.50, 2.54, 2.60, and 2.71 eV. Experiments were conducted by crossing a mass-selected, 8 keV ion beam with a linearly polarized laser beam, and measuring the kinetic energy distributions of the charged photodissociation products. By varying the angle between the ion beam and laser polarization, angular distributions were obtained at photon energies of 2.41 and 2.54 eV. The photon energy dependence of the average photofragment kinetic energies shows conclusively that photodissociation at these photon energies does not proceed by a direct dissociation process on a repulsive potential surface, or by a statistical vibrational predissociation process on a bound surface. The photofragment angular distributions are isotropic, providing further evidence that precludes direct photodissociation on a repulsive potential surface. Ab initio calculations were performed using the gaussian86 programs. These calculations indicate that ground state CO−3 has a planar D3h geometry, and 2A′2 electronic symmetry. This ground state correlates adiabatically to the CO−2 +O dissociation asymptote, not the lower energy O−+CO2 asymptote. Taken together, these new experimental and theoretical results suggest that the photodissociation of CO−3 at these energies occurs via the interaction of bound and repulsive excited state potential surfaces. A new model of the potential surfaces of CO−3 is proposed.

Mechanistic studies of processes involving carbon-carbon bond cleavage in gas-phase organometallic reactions using product kinetic energy release distributions: Co+ reacting with cyclopentane

A reverse-geometry mass spectrometer is used to obtain product ion kinetic energy release distributions to probe the energetics and mechanisms of several gas-phase organometallic reactions. In particular, we examine the mechanism for C{sub 2}H{sub 4} and C{sub 3}H{sub 6} elimination from Co(cyclopentane){sup +}. The kinetic energy release distribution associated with these processes can be modeled by using phase space calculations assuming, for the C{sub 3}H{sub 6} elimination process, propene rather than cyclopropane is being eliminated as the product neutral, and for the C{sub 2}H{sub 4} elimination process, Co(propene){sup +} rather than (cobaltacyclobutane){sup +} is being formed as the product ion. In addition, we obtain a heat of formation for the cobalt ethylene ion of 255 kcal/mol at 0 K, corresponding to a bond dissociation energy of 42 kcal/mol at 0 K, by fitting the theoretical results to the experimental distribution.

Threshold Fluence UV Laser Ablation of Single Crystal Bi2Sr2Ca1Cu2O8: Product Population and Kinetic Energy Distributions of Ejected Ionic Species

AbstractWe have conducted an experiment which measures the product population and kinetic energy (KE) distributions from the UV laser induced decomposition of crystalline Bi2Sr2Ca1Cu2O8. We have measured these distributions at two laser wavelengths 248, 351. At a third wavelength (355 nm) we have measured the photoejected mass spectra from both a single crystal Bi2Sr2Ca1Cu2O8 sample and a polycrystalline Bi2Sr2Ca2Cu3O10 sample. For all the experiments, the laser fluence is maintained near the threshold for ion formation. The laser fluences are well below the level for instigating a laser induced above surface plasma. Our results show that the ejected products are not the consequence of a laser surface evaporation process. We measure a wavelength dependence in the ejected species population distribution and the ejected kinetic energy distribution (< KE > = 5 ± 1 eV.2eV FWHM) is indicative of an electronic excitation process. The measured ion mass spectra show atomic, diatomic (e.g. Sr2+), and oxide (e.g. SrO+, CaO+) species with lesser quantities of the complex oxides (e.g. S2O+). Distinctly absent from the mass spectra are the oxide compounds BiO+, CuO+, and the atomic species O+. Furthermore, the mass spectrum shows that at 248 nm laser excitation, the Bi+ species is the abundant photopro-duct. However, for both the 351 nm and 355 nm excitations, the Sr+ and SrO+ ions are measured as more abundant. Also, comparing the 355 nm laser excitation of the single and polycrystalline samples, there is very little difference in the photoejected species mass spectrum.

UV Tunable Laser Ablation of YBa2Cu3Ox+6: Changes in the Product Population and Kinetic Energy Distributions as a Function of the Laser Wavelength and Target Bulk Temperature

ABSTRACTWe have conducted two separate experiments in the UV laser ablation of a sintered Yba2Cu3Ox+6wafer. We have measured the photoejected population distributions using selected UV laser wavelengths (4.01, 4.17 and 4.35 eV) near the 4.1 eV optical transition in Yba2Cu3Ox+6 In addition, we have measured the change in the ejected species kinetic energy as a function of the target bulk temperature. All the experiments were conducted at laser fluences well below the plasma formation threshold, and near that for product formation. Our results show that the UV laser ablation, at threshold fluences, proceeds via a nonthermal electronic excitation mechanism.

Threshold Level Laser Ablation of Yba2Cu3Ox+6 at 351 nm, 248 nm, and 193 nm: Ejected Product Population and Kinetic Energy Distributions

ABSTRACTUsing a sintered Yba2Cu3Ox+6 wafer in high vacuum, we have measured the photo-ejected products and kinetic energies at selected UV laser wavelengths (351 nm, 248 nm, and 193 nm) where the laser fluence is maintained near product formation threshold. At these fluences, we are well below the above surface plasma formation threshold and do not detect; any evidence for surface melting. Our results show that, for a specific laser wavelength, both the ion and the neutral mass spectrum agree. The measured spectrum shows that the photablated products consist only of atomic and diatomic species. In addition, the oxygen is bound only to the yttrium and barium. Our measurements further show that, for a specific ejected species, the yield is dependent on both the laser fluence and wavelength. However, the measured KE distribution is independent of the laser fluence for fluences near threshold. The species are ejected with mean KE between 6–9 eV and no species has kinetic energy in excess of 13 eV Our results imply that for UV laser threshold fluence ablation, the excitation/desorption process is nonthermal.

The chemistry of atomic transition-metal ions: insight into fundamental aspects of organometallic chemistry

For species as simple as atomic transition-metal ions, organometallic transformations usually involve multistep processes. These transformations have been studied with the entire arsenal of experimental techniques developed for the study of ion-molecule chemistry: conventional tandem mass spectrometry, flowing afterglow (FA) techniques, and ion cyclotron resonance (ICR) mass spectrometry and its Fourier transform adaptation (FT-ICR). In this Account, the authors limit ourselves to those methods in which motion along the reaction coordinate is the key dynamic variable that can be controlled as reactants approach and measured as the products recede. In our laboratories, guided ion beam techniques have been developed and highly refined for studies of the variation of reaction probabilities with E{sub T}. Complementing this work are measurements of product kinetic energy release distributions (KERDs).

ChemInform Abstract: Product Kinetic Energy Release Distributions as a Probe of the Energetics and Mechanisms of Organometallic Reactions Involving the Formation of Metallacyclobutanes in the Gas Phase.

ChemInform Abstract: Product Kinetic Energy Release Distributions as a Probe of the Energetics and Mechanisms of Organometallic Reactions Involving the Formation of Metallacyclobutanes in the Gas Phase.

Photodissociation dynamics of Ar 3+

Mass selected Ar 3 + clusters are photodissociated by a polarized argon-ion laser beam at 514, 488 and 458 nm. Only Ar +/2Ar products are observed. Laser polarization dependence of the product laboratory kinetic energy peak shapes indicates that a “pure” parallel transition is responsible for the photodissociation. Analysis indicates it is almost certainly a 2Σ u + ← 2Σ g + transition resulting in Ar + ( 2P 1 2 ). The product kinetic energy distribution is strongly bimodal with approximately 75% of the products at high kinetic energy (near the energy conservation limit) and 25% with near zero kinetic energy. A model is developed that explains this unexpected (and dynamically informative) result.

Product kinetic energy release distributions as a probe of the energetics and mechanisms of organometallic reactions involving the formation of metallacyclobutanes in the gas phase

Product kinetic energy release distributions as a probe of the energetics and mechanisms of organometallic reactions involving the formation of metallacyclobutanes in the gas phase

Kinematic averaging effects in thermal and low energy ion–molecule collisions: Influence on product ion kinetic energy distributions

The broadening and the shift of the kinetic energy distributions of the product ions from ion–molecule reactions caused by the velocity distributions of the reactants is discussed for different experimental situations. For a completely thermalized system (e.g., ions in an ideal trap) it is shown analytically that the product ion energy distribution is independent of the angular dependence of the differential cross section. In most of the cases of practical interest, the laboratory product velocity distribution for a state to state process can be approximated by a generalized Maxwell–Boltzmann distribution. Provided the exothermicity exceeds a few kT, the mean value of the corresponding energy distribution deviates from the nominal one by 3/2kT, and its half width increases with the square-root of the translational exoergicity ΔET i.e., FWHM=(11.09⋅m′1⋅m2/M2⋅ (ΔET+1.5⋅kT)⋅kT)1/2. If the ionic and neutral reactants are not in thermal equilibrium, the laboratory kinetic energy becomes strongly dependent not only on the energetics but also on the differential cross section. The problem is formulated in a rather general way and then applied to different experimental methods where the product ion velocity is used directly (e.g., in KEICR, guided ion beam, and differential scattering experiments) or indirectly (e.g., in LIF experiments for the density to flux conversion) to extract information on the energetics of a collision process. The results are used to analyze recent measurements on the collision systems N++CO, Ar++CO, Ar+++He, and H++D2 and it will be shown that a good estimate of the total resolution function is needed for a critical analysis of experimental data.

Dynamics of the condensation reactions of C+ with C2H4 and C2H2

The condensation reactions of C+ with C2H4 and C2H2 yielding new carbon–carbon bonds have been studied with crossed beam methods in the collision energy range from 0.5 to 1.5 eV. The data show that the reactions take place through short-lived collision complexes living a fraction of a rotational period. These results are shown to be consistent with schematic potential energy surfaces constructed from heats of formation and molecular structure calculations indicating that the large exothermicities of the reactions in comparison with the stabilities of intermediate C3H+4 and C3H+2 complexes should yield lifetimes in the 10−13 s regime. The data for C3H+2 formation from the reaction of C+ with C2H4 suggest two distinct production channels. These results are consistent with photoion-photoelectron coincidence breakdown curves for C3H+2 formation in the dissociative ionization of C3H4 isomers. The least exothermic reaction, C3H+ from reaction with ethylene, shows behavior in closest agreement with statistical predictions, specifically product kinetic energy distributions that scale with the total energy accessible to the products. This result is also in qualitative agreement with the nature of the potential energy surface mediating the reaction and lifetimes expected from the reaction energetics.

Photodissociation dynamics of small ionic clusters. The O +2 · (CO 2) 2 trimer

The photodissociation dynamics of the cluster O + 2 · (CO 2) 2 are studied in a crossed ion beam/laser beam machine from 590 to 458 nm. Absolute photodestruction cross-sections are obtained by comparing with previously measured (CO 2) + 2 cross-sections. The values increase monotonically from immeasurably small at 590 nm to 8 × 10 −18 cm 2 at 458 nm. This variation is very similar to previously measured cross-sections of O +·CO 2 and totally dissimilar to (CO 2) + 2. Hence, the chromophored in O + 2·(CO 2) 2 is deduced to be O + 2·CO 2. Branching ratios are measured at all wavelengths. The CO + 2 ion dominates at all wavelengths varying from 75% at 514 nm to 100% at 458 nm. Small amounts of (CO 2) + 2 and O + 2 ionic product are observed at 514 nm and less at 488 nm. Formation of the CO + 2 photoproduct takes essentially all of the energy available from the photon. Arguments are made that the mechanism for formation of this product occurs via a two-step process. Evidence to support this interpretation is drawn from an asymmetry parameter analysis of the product angular distributions and from the measured product kinetic energy distributions. Absorption of the photon directly accesses a repulsive state of the O + 2·CO 2 chromophore leading instantaneously to CO + 2/O 2 products. The CO + 2 ion forms a transitory complex with the remaining CO 2 molecule as it tries to escape from the cluster. The greatest percentage of these ions subsequently dissociate to CO + 2/CO 2 but a small percentage survive as (CO 2) + 2 products. Collision-induced dissociation yields predominantly the lowest energy products, O + 2·CO 2/CO 2, in contrat to photodissociation where no O + 2·CO 2 was observed. Suggestions about the possible mechanism are given.

N28orbiting interaction

The charge and mass distribution of orbiting yields from the $^{28}$Si${+\mathrm{}}^{14}$N interaction have been studied at center of mass energies between 30 and 56.7 MeV. The data indicate that the orbiting system lives sufficiently long for the exit channel yields to be determined by phase space considerations. The data are compared with compound nucleus and orbiting calculations, and clearly favor the latter. Further comparisons between the data and the orbiting calculations indicate that full phase space equilibration of the orbiting yields is hindered at low excitation energies by the inaccessibility of single nucleon transfer channels. Also evident in the data is a correlation in the behaviors of the charge width, mass width, and final product kinetic energies, which is interpretable as arising from a maximum angular momentum that the $^{28}$Si${+\mathrm{}}^{14}$N orbiting composite can sustain.

Systematics of thick-target recoil properties of deep spallation and fragmentation productions of high-energy proton reactions

Abstract Thick-target recoil properties of deep spallation and fragmentation products of the interaction of lanthanum, terbium, and lutetium with 800 GeV protons have been measured. The results yield the values of the mean product kinetic energies and, combined with previously reported angular distributions, those of the velocity of the remnant, β ∥ . The systematics of these quantities are examined both for these and other targets, ranging from silver to uranium.

A critical comparison of reactive etching of materials in microelectronics, fusion and space technologies

Chemical and radiation-enhanced gas-solid etching of materials that are important in microelectronics, fusion and space technologies, are compared and reviewed. Existing evidence suggests that the basic processes that drive spontaneous etching of several etchant-material combinations may be similar: F/Si, H/Si and H/C can be cited as examples. On the other hand, many etchant-material systems appear to involve system-specific processes that should not be generalized: examples are the XeF 2/Si and Cl/Si systems. Experiments show that when chemical etching is the dominant phenomenon, energetic particle or photon bombardment generally enhances etching by thermalized neutral active species. In microelectronic materials etching, investigators have systematically studied etching product yield and product kinetic energy as a function of ion mass, ion energy and angle of incidence; data on temperature dependence of etching are more limited. By contrast, the temperature dependence of etching C and C-composites in fusion technology has been studied extensively, but there is a lack of data on ion mass and angle dependence, and on the kinetic energy of products. There appears to be no comparable data on ion-assisted etching of materials in typical space environments. These fundamental parameters are essential for formulating and testing models of ion-enhanced etching chemistry. The available data are discussed in terms of phenomenological models and calculations that have been developed. It is clear that further work will be required to provide a solid understanding of the phenomena discussed in this review.