Dissociative excitation of selenium atoms in collisions of electrons with Se2 molecules

The dissociative excitation of selenium atom by electron impact is investigated for the first time under conditions of narrow composition of molecular beam. The thermal destruction of heavy Se_n molecules is used to obtain a beam with prevailing Se₂ molecule. Seventeen cross sections of dissociative excitation of SeI are measured at electron energy of 50 eV. Possible reactions of formation of excited selenium atoms in e-Se₂ collisions are discussed.     

Stripping of fast helium-like ions in multiple collisions with diatomic molecules

Cross sections of single and double stripping of fast helium-like Fe²⁴⁺ ions upon collisions with N₂ molecules have been calculated by nonperturbative methods for the impinging ion energies of 10, 100, and 1000 MeV/nucleon. It is shown that an allowance for the multiple collisions leads to significant differences between the projectile stripping cross sections for the target molecules oriented parallel and perpendicular to the incident particle velocity, whereas for chaotic orientations, this difference is insignificant.     

The excitation of odd levels of NdII in collisions of electrons with neodymium atoms

The method of extended crossing beams is used to investigate the excitation of transitions between the levels of a singly charged neodymium ion, which are excited as a result of single collisions of electrons with neodymium atoms (excitation with simultaneous ionization). The optical excitation functions in the electron energy range from zero to 200 eV are registered for all of the investigated transitions. The levels of sextet terms of configuration 4f⁴(⁵I)6p are excited most effectively.     

A thermal excitation mechanism of electronic states of diatomic molecules behind a shock front

On the example of CN and C₂ we consider the mechanism of efficient excitation of electronic states of diatomic molecules behind a strong shock front at temperatures of 4000–8000°K.Notation AC and AB diatomic molecules - A, B, and C atoms - AB^*, AB^** molecules in excited electronic states - M^* electronically excited molecule or atom, or a vibrationally excited molecule with a high level of excitation - M arbitrary component of the gas mixture - AB_v vibrationally excited molecule in the electronic ground state - AB_v ^* vibrationally excited molecule in one of the higher electronic states - vibrationally excited molecule in an intermediate electronic state - vibrationally excited molecule in the emitting electronic state (these states are B² for CN and d³_g for C₂) - ₁, ₂ lifetimes of the electronic states - k_j, k_-j rates of the forward and reverse reactions, respectively (j=6,..., 10) - K_j equilibrium constants of the reactions - e. g. in [AB] the square brackets refer to the concentration of molecules in the corresponding electronic state. The index eq refers to equilibrium conditions, and st refers to the concentration in the steady-state region behind the shock front Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 40, No. 3, pp. 410–415, March, 1981.     

Coherent cold collisions with neutral atoms in optical lattices

By loading a Bose-Einstein condensate into a three-dimensional optical lattice potential, we have been able to demonstrate several fundamental aspects of coherent cold collisions between neutral atoms. We show experimentally how such collisions lead to a well-defined phase shift in the corresponding many-body wave function. The experimental realization of such interactions can be fundamental for the simulation of complex condensed-matter-physics Hamiltonians, for the creation of large-scale entanglement and for the realization of quantum gates with neutral atoms.     

Spin exchange rate constant for collisions of metastable helium atoms with rubidium atoms

The spin exchange rate constant C _se in the He(2³S₁)-Rb(5²S_1/2) system has been measured for the first time in experiments on the optical orientation of metastable helium atoms in the presence of rubidium atoms. In the temperature interval T = 293–348 K, this value is C _se = (1.8 ± 0.4) × 10^?9 cm³ s^?1. The chemiionization rate constant, which has been simultaneously measured in collisions of these particles, is C _ci = (3.1 ± 0.6) × 10^?9 cm³ s^?1.     

Activation of diatomic molecules at solid surfaces

The interaction of a diatomic molecule with a well-defined single crystal surface represents the prototype of the elementary processes involved in heterogeneous catalysis, and it can be studied down to atomic length and extremely short (fs) time-scales. Our present understanding is illustrated by examples concerning the activation of hydrogen (including also the breakdown of thermal equilibrium during rapid laser-induced associative desorption), the role of steps as 'active sites' in the dissociative adsorption of NO or N2, and the mechanism and kinetics of the catalytic oxidation of CO.     

Spin exchange cross sections for collisions of metastable helium atoms with lithium atoms in the ground state

The spin exchange and chemi-ionization cross sections for the metastable helium atom-lithium atom in the ground state system have been calculated. Using data on the interaction potentials obtained in this study, the spin exchange cross sections are determined for the first time for the He(2³ S ₁)-Li(2² S _1/2) system in the interval of collision energies from 5 × 10^?3 to 16 eV.     

Potentials of internuclear interaction of diatomic molecules in planetary atmosphere

A method is given for the calculation of Ridberg—Klein—Rees potentials (RKR potentials) of internuclear interaction of diatomic molecules, which is based on a combination of numerical and analytical computer codes. A calculation of potentials of internuclear interaction is performed for 32 electron states of N₂, N ₂ ⁺ , C₂, CO, CO⁺, and CN molecules of practical interest as regards problems in aerophysics of interplanetary space vehicles. Complete spectral information is given for the calculation of potential curves, which may be used for unique comparison of the results of calculations of internuclear potentials obtained by different methods.     

Electron transfer and projectile excitation in single collisions

Studies of electron transfer (capture) and projectile excitation occuring together in a single encounter are reviewed. This combined capture and excitation can result from either a correlated or an uncorrelated interaction. The correlated process is referred to as resonant transfer and excitation (RTE), while the uncorrelated process is called nonresonant transfer and excitation (NTE). RTE is analogous to dielectronic recombination (DR) which occurs in the interaction between an ion and a free electron. Experimental and theoretical works leading to establishing the existence of RTE are reviewed as well as considerations relevant to distinguishing RTE from NTE. The dependences of RTE on projectile atomic number (14≤Z≤23) for Li-like ions, and on projectile charge state for H-like to Ne-like ions have been measured and compared with theory. The effect of the target electron momentum distribution on RTE has been demonstrated by comparing measurements for H₂ and He targets. Measurements of RTE involving L-shell excitation have been conducted and compared with K-shell results. All of the measured RTE cross sections to date for H₂ and He targets are in reasonable agreement with calculations based on theoretical DR cross sections averaged over the target electron momentum distribution; however, systematic discrepancies between experiment and theory exist. Additionally, it has been found that RTE can contribute considerably to total single-electron capture cross sections in the region where RTE is important, accounting for nearly half of the total capture events for calcium ions colliding with H₂.     

Strong-field ionization of heteronuclear diatomic molecules in circularly polarized laser fields

Abstract

We theoretically investigate the strong-field ionization of heteronuclear diatomic molecules, CO and NO, by calculating the photoelectron angular distribution and the photoelectron momentum distribution in circularly polarized fields. We find that the photoelectron angular distribution and the photoelectron momentum distribution of CO are inversion asymmetric, but symmetric about the molecular axis, most of the photoelectrons are ejected from the neighborhood of the C core. In contrast, for NO the photoelectron angular distribution and photoelectron momentum distribution are nearly fourfold symmetric about the molecular axis and its vertical axis, which means that the photoelectrons are equally ejected from the neighborhood of the N and O cores. By our results, the photoelectron angular distribution and photoelectron momentum distribution can be used to imprint the molecular orbitals.     

Spin polarization of 85Rb atoms in collisions with optically oriented metastable 4He atoms in alkali–helium plasma

Technical Physics Letters - We have experimentally detected a signal of magnetic resonance (MR) from 85Rb atoms in the 52 S 1/2 state by measuring the absorption of light from a helium lamp...     

Calculation of radiation characteristics of diatomic and some triatomic molecules

A mathematical model and a software package that permit calculation of the chemical composition of complex mixtures in a wide range of temperatures and densities are developed. A thermodynamic databank for a large number (about 300) of molecules and radicals up to pentatomic ones inclusive is set up. The chemical composition is determined in the approximation of local thermodynamic equilibrium. A mathematical model and a software package for calculating electron-vibration-rotation spectra of diatomic molecules are proposed. A databank of optical characteristics of molecules makes it possible to calculate spectra of about 50 of the most important molecules. The calculation is performed in the approximation of Morse potential—nonrigid rotator. A version for calculating spectra in the approximation of the Rydberg—Klein—Reese potential is also set up.     

A model for transport of diatomic molecules through elastic solids

Summary The distribution function of diatomic molecules, dissolved in a solid matrix subject to thermal elastic motion, was evaluated in closed form, assuming separability between the translational and rotational degrees of freedom of the solute molecules. The approach was applied to studying the transport of oxygen molecules through atomistic microstructures of atactic poly(vinylchloride) of ca. 40 Å at 318 K. The solubility coefficient was determined from the normalization constant of . The diffusion coefficient was evaluated from the long-term random walks of O₂ molecules on the network of local maxima of . Comparison with experimental data resulted in satisfactory agreement, indicating the viability of the approach.     

Impact excitation of squeezed vibrational packets in molecules

An analysis is made of vibrational packets created in molecules by collisions with fast protons. Some characteristic features of the Raman light scattering spectrum are discussed for a molecule with squeezed vibrational states. It is suggested that squeezed vibrational states in the ground electronic state of a molecule may be used for isotope separation. Pis’ma Zh. Tekh. Fiz. 24, 34–38 (July 12, 1998)     

A semi-classical description of excitation in sputtering and in electron-atom collisions

The application of a simplistic, semi-classical approach for describing excitation in sputtering and in electron-atom collisions is discussed. It is shown that the approach is able to describe relative populations when Si I, Si II and Si III are formed in sputtering as well as relative populations when Rb I, Rb II and Rb III are formed in electron-atom impact. The approach also compares favorably with the Born-approximation calculations of Vainshtein et al. for Rb I, provided it is again used to describe populations in a relative (rather than absolute) sense.     

Vibration and orientation of diatomic molecules flowing through small carbon nanotubes

With their unique long cylindrical shape, carbon nanotubes may one-day form nozzles for nano-scale printing or flow into a chamber. Since the scale of the flowing molecules is similar to the diameter of the nanotubes, molecular vibration, orientation and density become influenced by the confinement during flow. We have studied the flow of diatomic molecules through carbon nanotube nozzles using non-equilibrium molecular dynamics simulations, in an effort to gain a greater understanding about the fundamental properties of such molecules in such a setting. The frequency of vibration of the molecules is shown to be dependent on the density inside the nanotubes and follow the same relation as an experimental micro-scale density-frequency study suggests, although only for nanotubes above a certain diameter. Meanwhile no relation is found between the frequency of vibration and the flow rate. The effect of nanotube diameter on the orientation of the molecules is also examined in detail, showing the transition between axial and radial orientation, with "pull" and "push" effects determining the orientation.     

Inelastic collisions of molecules within the SFO model

An inelastic collision of diatomic molecule AB with structureless particle M (VT energy exchange) is considered within the SFO/SFHO model. An approach for determining the energy efficiency of excitation of molecular vibrational levels, energy-loss matrix, and total energy loss in a head-on collision with molecules/atoms is proposed. Nitrogen molecules N₂ are chosen as AB and M. An interaction in the AB–M system is described using the “improved” Lennard-Jones potential.     

Orientational effects in adsorption I: An ideal localized monolayer of diatomic molecules

Classical statistical mechanics is used to calculate the thermodynamic properties of a localized monolayer of diatomic molecules adsorbed on a crystalline solid. Explicit results are presented for adsorption of homonuclear diatomic molecules on the exposed (100) face of a simple cubic lattice. The configurational heat capacities calculated for several systems indicate that adsorbed molecules undergo a gradual transition from hindered to free rotation as the temperature is raised. It is also found that the temperature at which the above transition occurs depends strongly on the relative sizes of the solid and adsorbate atoms. The conclusions derived from the heat capacity results have been confirmed by the calculation of the one-particle orientational distribution function for adsorbed molecules.