Collisions Of Molecules Research Articles

Triatomic Photoassociation in an Ultracold Atom–Molecule Collision

Ultracold collisions of neutral atoms and molecules have been of great interest since experimental advances enabled the cooling and trapping of such species. This study develops a simplified theoretical treatment of a low-energy collision between an alkali atom and a diatomic molecule accompanied by absorption of a photon from an external electromagnetic field. The long-range interaction between the two species is treated, including the atomic spin-orbit interaction. The long-range potential energy curves for the triatomic complex are calculated in realistic detail, while effects of the short-range behavior are mimicked by applying different boundary conditions at the van der Waals length. For neutral colliding species, the leading interaction term is the dipole-dipole interaction. In the case of nonpolar dimers like Cs2, the second leading term is the quadrupole-quadrupole interaction. However, there is also a strong dipole-quadrupole interaction for dimers with a large permanent dipole moment such as NaCs, making the dipole-quadrupole interaction the second leading term for an atom colliding with a polar dimer. Our applications of the simplified treatment show a higher density of trimer states for a polar dimer compared to the case of a nonpolar dimer like Cs2. This is a consequence of the strong quadrupole-dipole coupling between the atom and the dimer dipole moment.

Thermal stability of a mixed working fluid (R513A) for organic Rankine cycle

Organic Rankine cycle (ORC) is an effective way to utilize low-grade energy, with R1234yf being considered a promising working fluid for ORC for its low global warming potential (GWP). Nevertheless, the weak thermal stability has limited the application R1234yf in ORC, emphasizing the necessity to find a way preventing the its pyrolysis in ORC. In this connection, a systematic study on the mechanism of R134a affecting the thermal stability of R1234yf in ORC was conducted in this work. Our experimental results indicate that the pyrolysis temperature of R513A (R1234yf/R134a) is in the range of 190–210 °C. Further, ReaxFF simulations and density functional theory (DFT) calculations were performed on the pyrolysis process of R1234yf, R134a and R513A. It is revealed that the main pyrolysis reaction pathways of working fluids can be divided into three types: the reactions of working fluid molecules collision with F radical (FCR) or H radical (HCR), and the self-decomposition reactions of working fluid molecules (SDR). In R513A, F and H radicals are the origin for the affected thermal stability of R1234yf. The results are of great significance to guide the selection of additive species to enhance the thermal stability of HFO working fluid.

Multi-UCAV Cooperative Target Allocation Based on Energy-Reserved Chemical Reaction Algorithm (CNCRO)

Aimed at the disadvantages of constrained processing technology in the cooperative target allocation of multiple unmanned combat aircraft (UCAV), the energy-reserved chemical reaction algorithm (CNCRO) is proposed to solve the constrained optimization problems. On the one hand, convert multiple constraint conditions of the multi-UCAV target allocation into optimization targets to transform the constrained processing problem into a multiobjective optimization problem including allocation goals and constrained optimization goals. On the other hand, the energy-reserved chemical reaction algorithm (CNCRO) is proposed, which introduces the environmental energy-reserved variables buffer into the ineffective collision, combination or splitting reactions between single molecule and multimolecules of CNCRO, which is used to boost energy for the low kinetic energy molecules, so as to reduce its kinetic energy in case of invalid collision of molecules and control it to gradually stabilize and converge. At the same time, the splitting reaction is inspired, to greatly change the structure of molecules, promote its search for more solution space, and improve the splitting reaction ability and its global optimization ability. Finally, the simulation experiment is completed by using MATLAB software. The advantages of CNCRO in accuracy are verified by 8 standard test functions, the influence of the weight coefficients in the cooperative target allocation function of UCAV is studied, which are revenue, loss, and voyage, and the target allocation schemes of traditional constrained processing and unconstrained multiobjective optimization methods based on different attack target number C i and total target number N are investigated, to obtain the control law, which can be used to guide the given parameters with different emphases.

Study on the explosion characteristics of propanal/air mixtures at elevated pressures

Propanal is a crucial intermediate speciates generated from the combustion of biofuels. To understand its formation pathways and optimize the clean combustion of biofuels, accurate determination of its laminar burning speed at engine-like conditions is essential. Additionally, propanal can be used to produce propionic acid by reacting with air under elevated pressures, which is a process that inherently poses a significant explosion risk. To address the above issues, the effects of initial pressures (0.1–1.0 MPa) and fuel concentrations (2.56–9.52%) on the explosion pressure and laminar burning speed of propanal/air mixtures were investigated. Results show that the relationship between the explosion pressure and fuel concentration was satisfactorily fitted by a cubic polynomial function. By comparing the laminar burning speed obtained using the constant volume method (CVM) and kinetic studies, the reliability of the kinetic model at elevated pressure was verified. According to the sensitivity analysis of elementary reactions affecting the flame temperature, the major elementary reactions affecting the combustion of propanal were analyzed. From fuel-lean to stoichiometric concentration, the combustion of propanal is dominated by the reaction kinetics of H2 and CO, while alkyl relevant mechanism controls the kinetics at fuel-rich conditions. At the fuel-lean conditions, recombination reactions were triggered during the collision of the excess oxygen molecules with reactive radicals. However, on the fuel-rich side, recombination reactions involving O2 progressively weakened. In addition to being affected by the equivalent ratio, elementary reactions are also profoundly influenced by the initial pressure. However, the effect of initial pressure on the elementary reactions is influenced by the fuel concentration. As the concentration of propanal is below the stoichiometric concentration, the sensitivity of elementary reactions increases gradually with the increasing initial pressures, while it no longer varies monotonously as the equivalence ratio reaches 1.5.

Collisional losses of ultracold molecules due to intermediate complex formation

Understanding the sources of losses and chemical reactions of ultracold alkali-metal molecules is among the critical elements needed for their application in precision measurements and quantum technologies. Recent experiments with nonreactive systems have reported unexpectedly large loss rates, posing a challenge for theoretical explanation. Here, we examine the dynamics of intermediate four-atom complexes formed in bimolecular collisions. We calculate the nuclear spin--rotation, spin--spin, and quadrupole coupling constants for bialkali tetramers using ab intio quantum-chemical methods. We show that the nuclear spin--spin and quadrupole couplings are strong enough to couple different rotational manifolds to increase the density of states and lifetimes of the collision complexes, which is consistent with experimental results. We propose further experiments to confirm our predictions.

The molecular dynamics simulation of lignite combustion process in O2/CO2 atmosphere with ReaxFF force field

Pressurized oxy-fuel combustion is a complex process consisting of free radical collisions and reactions. ReaxFF reactive Molecular Dynamics (MD) simulation method is a useful tool to investigate the chemical events in coal combustion at atomistic level. In this work, the impact of operating conditions on the distribution of main fragments and the reaction mechanisms were examined using a lignite coal model with ReaxFF force field to simulate the process of oxy-fuel combustion under pressures. The ReaxFF MD simulations found that the decomposition of coal molecular structure would be enhanced by increasing the pressure/density, oxygen concentration and temperature. The variety of initial reactions increased with temperature. Increasing pressure promoted the effective collision of molecules and the coal structure was more likely to be attacked by oxidants, so the chemical bonds in coal molecule broke earlier and the consumption of O2 increased at higher pressure. The dehydrogenation reaction on the macromolecular structure of coal and small fragments was also promoted after increasing pressure/density. However, the number of fragments decreased as the pressure/density continued to grow, because large fragments further decomposed or some small molecular benzene ring structures with less than 6C atoms were re-polymerized. The dehydrogenation reaction of coal molecule and small fragments was promoted after increasing the pressure. O2 attacked the benzene ring structure, the C atom on the outer side of the coal, and the carbon-containing fragments in the system, indicating that the increase of O2 concentration promoted the ring opening and oxidation reactions, thereby promoting the decomposition and combustion of coal. The work in this paper has confirmed the findings obtained by other oxy-fuel experimental work from the microscopic point of view.

Model two-particle kinetic equation for pairs of quasiparticles

Because the main process of interaction in the Boltzmann model of real gases is the binary collision of molecules, it is convenient to use the two-particle kinetic equation to describe the dynamics of a rarefied gas. This equation was written using the same physical assumptions as those used by Ludwig Boltzmann. The right-hand side of this equation contains the product of the linear scattering operator and chaos projector. The Boltzmann equation follows from this equation without any additional approximations after simple integration of the velocities and positions of the second particle. Using the divergence form of the scattering operator, this equation can be represented as the Liouville equation, which implies that real molecules can be replaced by quasiparticles whose distribution function is the same as that of real molecules but whose dynamics are completely different. Pairs of quasiparticles do not collide but move along continuous trajectories in the phase space. The relative velocities in pairs of quasiparticles slowly rotate with an angular velocity vector depending on the distribution function. We provide an explicit approximate expression for the angular velocity through the first few velocity moments, using a special covariant Grad expansion for the velocity distribution function, which reduces to the exact Bobylev–Kruk–Wu solution in the isotropic case. We simulated the relaxation of distribution function to equilibrium and compared results with the existing exact solutions. The described algorithm will be effective for modeling flow regions with low Knudsen numbers, where the standard Direct Monte Carlo Simulation (DSMC) method encounters significant difficulties.

Transition Gas Flow Between Two Parallel Plates with a Slit-Type Obstacle of Various Geometry by Event Driven Molecular Dynamics Simulation

In this study, pressure-driven flow through a slit-type obstacle with various length (L) and height (H) placed in between two parallel plates was investigated by Event Driven Molecular Dynamics (EDMD) simulation. Mach number, temperature and pressure distributions were obtained along the channel in the transition regime. The change in these macroscopic properties and flow rate were examined for different cases created by changing Knudsen number (Kn) of the gas, the geometry of the slit and the outlet/inlet pressure ratio of the flow. Collision of gas molecules with plates and the obstacle were modeled with diffuse reflection boundary condition. The flow rate showed a sudden change in the transition regime and significant differences in the molecular regime depending on the pressure ratio. Except for the Kn, H and L dimensions were found to be effective in Mach disc formation. Pressure drops at the exit of the slit were shaped differently in normalized pressure profiles depending on Kn, H and L dimensions. In addition, the structure of the vortices formed at the entrance and exit of the slit varies depending on Kn. Some of the results obtained were confirmed to be consistent with the similar studies in the literature.

Molecular dynamics simulation of the transport properties and condensation mechanism of carbon dioxide

The application of supersonic gas separation technology to remove carbon dioxide (CO2) from natural gas is an emerging concept; however, the microscopic mechanisms of CO2 condensation remain unknown. The accuracy of various CO2 flexible force field models is evaluated in this study, and the CO2 nucleation and growth processes are elucidated using molecular dynamics simulations. The results show that the ZHU model predicts CO2 density, self-diffusion coefficient, shear viscosity, and vapor–liquid phase interface thickness with high accuracy. At low temperatures, CO2 molecules can spontaneously nucleate. The subsequent droplet growth is determined by the collision of monomer molecules with clusters as well as the merging of clusters. The mass transfer of the CO2 condensation process is aided by the droplet growth process. Furthermore, the lower the cooling temperature and the higher the initial pressure are, the shorter is the time required for CO2 nucleation, the higher is the nucleation rate, and the faster is the liquefaction. Furthermore, the temperature control method that directly controls the overall temperature of the system was discovered to force the removal of the heat transfer process from clusters to CO2 molecules, and the carrier gas temperature control method should be used in subsequent indepth research.

Застосування числових методів газодинамічних розрахунків в задачах обтікання перешкод розрідженим струминним потоком

The development of competitive space hardware calls for continuing improvements in the accuracy of simulation of gas-dynamic processes in the space vehicle vicinity. This may contribute to extending the active life of spacecraft, thus improving the economic efficiency of space activities. In particular, quite a topical problem is the simulation of the interaction of rarefied jets from the propulsion system of a spacecraft with its individual components. To solve this problem in the case of a rather high surrounding vacuum, use is made of the molecular-kinetic concept of the gas structure based on the Boltzmann equation. The aim of this paper is to overview existing methods of simulation of gas-dynamic processes near spacecraft in a rarefied gas flow with account for propulsion system jets and to choose the most promising approaches to the solution of this problem. Among the methods considered, several main lines are set off: approximate, analytical, and numerical methods. Approximate methods use physical models of jet flow, approximation of numerical results, or a combination of both approaches. Analytical methods are based on essentially simplified assumptions and are intended for a very narrow class of problems. Numerical methods are the most universal tool of theoretical study. At the same time, each numerical method has a range of application of its own. At present, the most used and promising methods are statistical simulation methods: the direct simulation Monte Carlo method (DSMCM) and the test particle method (TPM). The former splits the continuous process of molecule motion and collisions in a rarefied gas into two successive independent stages (free-molecular transfer and relaxation) at each small time step. The simulation is done by time steps and in fact reproduces a nonstationary process. The latter, the TPM, consist in a statistical successive simulation of the wandering of test particles (molecules) on the background of field ones about the cells of the computational grid. Test particles, which move within the cells of the computational area, periodically collide with the obstacle in the flow and field particles, and in doing so they gradually change both their velocity and the field characteristics. For both statistical approaches, the simulation accuracy, as can be expected, is inversely proportional to the square root of the number of tests: the number of time steps and modeling particles for the DSMCM and the number of successively simulated test particle trajectories for the TPM. This may greatly affect the possibility of attaining a desired accuracy.

Coherent multichannel optical theorem: Quantum control of the total scattering cross section

The optical theorem is a fundamental aspect of quantum scattering theory. Here, we generalize this theorem to the case where the incident scattering state is a superposition of internal states of the collision partners, introducing additional interference contributions and, e.g., providing a route to control the total integral cross section. As in its standard form, forward scattering plays an essential role in the multichannel optical theorem, but with interference terms being related to the inelastic forward scattering amplitudes between states in the initial superposition. Using the resultant control index, we show that extensive control is possible over ultracold collisions of oxygen molecules in their rovibrational ground states, and of $^{85}\mathrm{Rb}\text{\ensuremath{-}}^{85}\mathrm{Rb}$ collisions, promising systems for the experimental demonstration of the quantum interference control of the total scattering cross section.

Microwave-assisted catalytic alcoholysis of fructose to ethoxymethylfurfural (EMF) over carbon-based microwave-responsive catalyst

Ethoxymethylfurfural (EMF) is a promising fuel additive and biofuel which can be produced via catalytic direct alcoholysis of fructose. In this work, microwave-responsive catalysts were prepared by carbonization of cellulose (via either hydrothermal treatment or calcination) then functionalized with SO3H group (via impregnation using concentrated sulfuric acid), which exhibit remarkable performances in one-pot catalytic conversion of fructose to EMF with ethanol. After a 8 h reaction under microwave irradiation at 75 °C, about 80.3% fructose conversion was achieved with the EMF yield of 61.2% for the carbon catalyst prepared by the hydrothermal treatment, which is much higher than that achieved by the catalysis promoted by conventional heating. Further investigation showed that with a microwave-responding catalyst, microwave irradiation encourages the formation of local hot-spots on the catalyst surface, thus facilitating the collision of reactant molecules with catalysts to improve the catalytic efficiency. This work demonstrates the potential of microwave-responsive heterogeneous catalysts for process intensification of valorization of bio-derived chemicals under microwave irradiation.

Fragmentation inside proton-transfer-reaction-based mass spectrometers limits the detection of ROOR and ROOH peroxides

Abstract. Proton transfer reaction (PTR) is a commonly applied ionization technique for mass spectrometers, in which hydronium ions (H3O+) transfer a proton to analytes with higher proton affinities than the water molecule. This method has most commonly been used to quantify volatile hydrocarbons, but later-generation PTR instruments have been designed for better throughput of less volatile species, allowing detection of more functionalized molecules as well. For example, the recently developed Vocus PTR time-of-flight mass spectrometer (PTR-TOF) has been shown to agree well with an iodide-adduct-based chemical ionization mass spectrometer (CIMS) for products with 3–5 O atoms from oxidation of monoterpenes (C10H16). However, while several different types of CIMS instruments (including those using iodide) detect abundant signals also at “dimeric” species, believed to be primarily ROOR peroxides, no such signals have been observed in the Vocus PTR even though these compounds fulfil the condition of having higher proton affinity than water. More traditional PTR instruments have been limited to volatile molecules as the inlets have not been designed for transmission of easily condensable species. Some newer instruments, like the Vocus PTR, have overcome this limitation but are still not able to detect the full range of functionalized products, suggesting that other limitations need to be considered. One such limitation, well-documented in PTR literature, is the tendency of protonation to lead to fragmentation of some analytes. In this work, we evaluate the potential for PTR to detect dimers and the most oxygenated compounds as these have been shown to be crucial for forming atmospheric aerosol particles. We studied the detection of dimers using a Vocus PTR-TOF in laboratory experiments, as well as through quantum chemical calculations. Only noisy signals of potential dimers were observed during experiments on the ozonolysis of the monoterpene α-pinene, while a few small signals of dimeric compounds were detected during the ozonolysis of cyclohexene. During the latter experiments, we also tested varying the pressures and electric fields in the ionization region of the Vocus PTR-TOF, finding that only small improvements were possible in the relative dimer contributions. Calculations for model ROOR and ROOH systems showed that most of these peroxides should fragment partially following protonation. With the inclusion of additional energy from the ion–molecule collisions driven by the electric fields in the ionization source, computational results suggest substantial or nearly complete fragmentation of dimers. Our study thus suggests that while the improved versions of PTR-based mass spectrometers are very powerful tools for measuring hydrocarbons and their moderately oxidized products, other types of CIMS are likely more suitable for the detection of ROOR and ROOH species.

A simple model for gas barrier performance of polymer nanocomposites considering filler alignment angle and diffusion direction

The available models for predicting the barrier properties of nanocomposite films cannot present the accurate results fitting to experimental data. In this paper, we develop a new model to forecast the barrier performance of polymer nanocomposites by filler orientation angle and changes in diffusion direction after collision of gas molecules to nanoplatelets. The developed model presents the barrier properties by the length, thickness, volume fraction and orientation angle of nanoplatelets as well as the lateral distance between adjacent nanoparticles. To gain a better understanding of the accuracy of new model, the predictions of permeability by previous models are compared to the experimental data of various samples containing nanoclay and graphene. The developed model offers the highest exactness among the models. The orientation of nanofiller in the polymer medium, degree of filler dispersion in addition to the aspect ratio and volume fraction of nanofiller are the most important factors affecting the barrier performance.

Observation of Chemical Reactions between a Trapped Ion and Ultracold Feshbach Dimers.

We measure chemical reactions between a single trapped ^{174}Yb^{+} ion and ultracold Li_{2} dimers. This produces LiYb^{+} molecular ions that we detect via mass spectrometry. We explain the reaction rates by modeling the dimer density as a function of the magnetic field and obtain excellent agreement when we assume the reaction to follow the Langevin rate. Our results present a novel approach towards the creation of cold molecular ions and point to the exploration of ultracold chemistry in ion molecule collisions. What is more, with a detection sensitivity below molecule densities of 10^{14} m^{-3}, we provide a new method to detect low-density molecular gases.

Stereodynamical Control of Cold Collisions of Polyatomic Molecules with Atoms.

Scattering between atomic and/or molecular species can be controlled by manipulating the orientation or alignment of the collision partners. Such stereodynamics is particularly pronounced at cold (∼1 K) collision temperatures because of the presence of resonances. Comparing to the extensively studied atomic and diatomic species, polyatomic molecules with strong steric anisotropy could provide a more sophisticated platform for studying such stereodynamics. Here, we provide the quantum mechanical framework for understanding state-to-state stereodynamics in rotationally inelastic scattering of polyatomic molecules with atoms and apply it to cold collision of oriented H2O with He on a highly accurate potential energy surface. It is shown that strong stereodynamical control can be achieved near 1 K via shape resonances. Furthermore, quantum interference in scattering of a coherently prepared initial state of the H2O species is explored, which is shown to be significant.

Electric field dependence of complex-dominated ultracold molecular collisions

Recent experiments on ultracold non-reactive dipolar molecules have observed high two-body losses, even though these molecules can undergo neither inelastic, nor reactive (as they are in their absolute ground state), nor light-assisted collisions (if they are measured in the dark). In the presence of an electric field these losses seem to be near universal (the probability of loss at short-range is near unity) while in the absence of it the losses seem non-universal. To explain these observations we propose a simple model based on the mixing effect of an electric field on the states of the two diatomic molecules at long-range and on the density-of-states of the tetramer complex formed at short-range, believed to be responsible for the losses. We apply our model to collisions of ground-state molecules of endothermic systems, of current experimental interest.

The Influence of Humidity on Electron Transport Parameters and Insulation Performance of Air

The environmental conditions affect the external insulation performance of power equipment. In order to study the physical characteristics of air discharge, the microscopic process of electron–molecule collision in the air based on the Boltzmann equation has been studied in this paper. The influence of humidity on the air gap insulation performance was also analyzed. The calculation results show that with the temperature 300 K and the pressure 1.0 atm, the electron energy distribution function and electron transport parameters varied with the air relative humidity. As the air relative humidity is increased by each 30%, the average electron energy decreases by about 0.2 eV, the reduced electron mobility decreases by about 0.25 × 1023 [1/(V·m·s)], the reduced electron diffusion coefficient decreases by about 0.2 × 1024 [1/(m s)], and the effective ionization coefficient decreases by about 4 × 10−24 m2. As the air relative humidity increases from 0% to 60%, the critical breakdown electric field increases by 1.22 kV/cm.

Application of Nanoporous Super Thermal Insulation Material in the Prevention and Control of Thermal Hazards in Deep Mining of Metal Mines

As an important energy material, mineral resources have an important role in the rapid growth of the national economy. In recent years, with the enhancement of mining strength and the improvement of mechanized production level, the depth of mining has also increased year by year. Therefore, the number of heat hazards in deep mine mining has increased year by year, and the problem of heat loss in deep mines has become increasingly prominent, which has seriously affected the safe and efficient production of mines. In this paper, the application of nanoporous super insulation materials in the prevention of thermal damage in deep mining of metal mines is studied, and the related theories of nanoporous super insulation materials and the prevention of thermal damage in deep mining of metal mines are understood on the basis of literature data. Nanoporous thermal insulation materials refer to thermal insulation materials with pore diameters in the nanometer range. This material can effectively prevent the collision of gas molecules and prevent the heat conduction of the gas. Then, the application experiment of nanoporous super thermal insulation materials in the prevention and control of heat damage in deep mining of metal mines is carried out. Through experiments, it is concluded that the room temperature thermal conductivity of the experimental material decreases with the increase of the addition of SiO2 aerogel, and the downward trend is linear, and when the heat source temperature is 200°C, the coating surface temperature of the thermal insulation material (excluding aerogel) is 100°C, and the thermal insulation temperature difference is 100°C, while when the coating surface temperature of the aerogel thermal insulation coating is only 60°C, the thermal insulation temperature difference is 140°C. From these data, it can be seen that the thermal insulation performance of nanoporous super thermal insulation materials is better, which verifies the feasibility of its application in the prevention of heat damage in metal mine mining.

Electron scattering cross sections for diazene (N[formula omitted]H[formula omitted]) and hydrazine (N[formula omitted]H[formula omitted

In this work, a computational study on electron interactions with diazene (N2H2) and hydrazine (N2H4) was performed; two conformations of N2H2 (E–N2H2 and Z–N2H2) were considered. Differential cross sections (DCS), integral cross sections (ICS), and momentum transfer cross sections (MTCS) for elastic scattering as well as total cross sections (TCS) and total absorption cross sections (TACS) were explored at incident energies from 0.1 to 500 eV. A molecular complex optical potential approach combined with Padé approximants was used for describing the electron–molecule collision dynamics and solving the scattering equations. Marked differences were noticed when the DCS for elastic electron–Z–N2H2 scattering were compared to the corresponding results for electron–E–N2H2 (particularly at low incident energies and small angles), a behavior which was assigned to the existence of a permanent dipole moment in the case of the Z–N2H2 molecule; results regarding N2H4 were found to be considerably more similar to those determined for Z–N2H2. In terms of ICS and MTCS, results obtained for E–N2H2 presented a first peak at 1.15 eV (originating from the 2Bg continuum symmetry and being related to the π∗ resonance arising from the nitrogen-nitrogen bond) and another at around 10 eV. These peaks can be related to the −N=N− moiety and to the existence of the N−H bonds, respectively. Interestingly, no peaks were clearly observed in Z–N2H2 ICS and MTCS while only the peak at around 10 eV was (barely) seen in the MTCS of N2H4, even without employing the Born-closure procedure. Hence, conformation plays a major role in probing the resonances for the N2H2 molecule, being the strong dipole moments responsible for masking the structures in the case of Z–N2H2 (as well as eventual additional peaks in N2H4). TACS results were found to be (practically) the same for both conformations of N2H2 at the energy range probed, being systematically lower than N2H4 TACS. In addition, the maxima of absorption was found at 70 eV for N2H4, which is slightly shifted when compared to the maxima probed for E–N2H2 and Z–N2H2 (observed at 80 eV).