Characterization of NeNe long range interaction by absolute total cross section measurement

Absolute total elastic cross sections for NeNe collisions have been measured in the 0.5–1.4 km s^?1 velocity range. The analysis of the data allowed accurate characterization of the interaction in a distance range between 3.9 and 5.3 A. This result implements the information previously obtained and improves the knowledge of the Ne₂ interaction potential.     

Orbiting trajectories and the adiabatic approximation to the capture cross section

For the potentialV(R)=CR ^?4(1+ε(cos²??1/2)) and a planar geometry we compute classical trajectories, which are a good approximation to those trapped orbits which separate collisions with “capture” from those without. Two possible types of such trajectories (rotating or librating in the rotating reference frame) and the transition between both types are discussed. From the limiting impact parameters accurate capture cross sections may be calculated. They can be compared with the popular approximation known as ADO — (average dipole orientation) — theory, but an analysis of the latter shows that it is theoretically not justified. Instead, the adiabatic approximation for planar collisions is developed with and without angular momentum conservation. It fits numerical calculations very well as long as the transition from rotation to libration lies inside the centrifugal wall, i.e. the separating orbit is a rotation. In the opposite case only qualitative agreement is obtained. Finally, a simple approximation to get 3D capture cross sections from planar calculations is discussed.     

Sudden approximation relations between tensorial cross sections for the collision of two diatomic molecules

We demonstrate relations between tensorial cross sections for the collision between two diatomic molecules, one of which does not rotate during the collision. The demonstration relies on a factorisation of the S matrix. A numerical example is presented for the rotational excitation problem of CO by H₂ (j = 1) molecules     

Determination of total attenuation cross section of carbon using secondary excitors in the energy range 4.5–60 keV

Experimental total attenuation coefficients of carbon in the photon energy range 4.5–60 keV have been measured. The total attenuation cross section of C rapidly decreased with energy in the range of 4.5–10 keV. The measured values are in agreement with the theoretical values.     

Measurements of the influence of the angular dependent intermolecular potential on the total collision cross section for molecular hydrogen and various scattering partners

For H₂ molecules colliding with Ar, Kr, Xe, CO₂, N₂ and SF₆ the total collision cross section is measured, applying state selection to the H₂ molecule. The preferential orientation of the H₂ molecule in the J = 1, m_J = 0 state is used to determine the influence of the angular dependent part of the intermolecular potential.     

Halfway house variational continuum distorted wave theory: high energy cross sections in the distorted wave perturbation approximation

The total cross section for charge transfer at high but non-relativistic energy is investigated within a new time-independent wave version of the halfway-house phase integral variational continuum distorted wave formalism, using simple first order perturbation theory. Following Crothers, Dubé and Brown this theory satisfies all known short and long range Coulomb boundary conditions which is essential if intermediate elastic divergences are to be avoided. The discussion is specialised to the particular case ofls →ls capture. Numerical results for this amplitude are obtained by a double numerical integration. Wave results derived for the capture process $$P^{Z_P^ + } + (T^{Z_T^ + } + e^ - ) \to (P^{Z_P^ + } + e^ - ) + T^{Z_T^ + } $$ in the caseZ _T = 1 =Z _P are compared with various theoretical impact parameter models and experimental data. Representative distributions of the total cross sections are presented as a function of the impact energy.     

Semiclassical analysis of the anisotropic total cross section in thermal energy collisions between a non-spherical and a spherical atom

Thermal energy atomic collisions of the typeA(² P _3/2)+B(¹ S ₀) are discussed to clarify the dependence of the orientational anisotropy Δσ in the total cross section σ on the relative velocityv. Simple expressions for Δσ/σ are derived by semiclassical treatments designed to be appropriate for large spin-orbit interactions. The Δσ/σ oscillates withv around its average value. The velocities giving the extrema in the oscillating curve are almost solely determined by the isotropic part \(\bar V\left( R \right)\) in the interaction potential, while the amplitude of the oscillation depends sensitively on the anisotropic interaction nearR _mi, whereR _mi is the location of the minimum in \(\bar V\left( R \right)\) . The oscillation-averaged Δσ/σ is independent of the relative velocity and proportional to the anisotropy in the van der Waals interaction.     

Absolute total electron-scattering cross section of H2S

Measurements made on H₂S in the energy range 1.3–70 eV give total electron-scattering cross sections which exhibit two distinct features: a shoulder at about 2.3 eV and a very broad hump centered at 9 eV with a maximum value of 40 × 10⁻²⁰ m². These results are in agreement with those calculated by Jain and Thompson and are completely different from the experimental data of Sokolov and Sokolova.     

Importance of collision cross section measurements by ion mobility mass spectrometry in structural biology

The field of ion mobility mass spectrometry (IM‐MS) has developed rapidly in recent decades, with new fundamental advances underpinning innovative applications. This has been particularly noticeable in the field of biomacromolecular structure determination and structural biology, with pioneering studies revealing new structural insight for complex protein assemblies which control biological function. This perspective offers a review of recent developments in IM‐MS which have enabled expanding applications in protein structural biology, principally focusing on the quantitative measurement of collision cross sections and their interpretation to describe higher order protein structures.     

A segmented radiofrequency-only quadrupole collision cell for measurements of ion collision cross section on a triple quadrupole mass spectrometer

The gas collision cell of a triple quadrupole mass spectrometer has been modified to consist of ten short quadrupole rod segments that allow an axial field to be applied to the cell in order to make measurements of ion mobility. The radiofrequency (rf)-quadrupole field provides effective radial confinement that greatly reduces diffusional losses at low pressure. The mobilities of mass-selected ions from an ionspray source have been measured at a pressure of 8 × 10^?3 torr at electric fields of 0. 1 to 3 V/cm, and used to calculate the collision cross sections of the ions. The measured cross sections compare well with those measured by other techniques.     

Equivalence and conservation rules for the total integral cross section in molecular collisions

The rule of conservation of the total integral cross section o_Tj) is described in a general way using the opacity function. An equivalence rule which states that at the same initial kinetic energy, the total integral cross section from the initial state j is equal to that from the initial state j, i.e., o_Tj) is also presented. Both rules are demonstrated with numerical examples in the He + H₂ collision system and counter-examples are also presented. Possible uses of the rules in the inversion of the intermolecular surface and as an experimental tool are also discussed.     

Calculation of molecular energy indices by the bond interaction method

Conclusions Parameters were determined for an interacting bond model for hydrocarbons and oxygen- and sulfur-containing organic molecules. The parameters obtained were used to calculate the homolytic bond dissociation energies and molecular formation energies.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1680–1683, July, 1988.     

Calculation of the potential energy surface of a polyatomic molecule in an adiabatic approximation

V. I. Vernadskii Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 6, pp. 1142–1144, November–December, 1995     

Energy dependence of reaction cross sections at high energy

The energy dependence of the total reaction cross sections for the reaction A + BC → AB + C is obtained in the sufficiently high energy regime, based on the Born approximation and the stationary phase approximation. The total reaction cross section (σ_t) which is a sum over all final vibrational and rotational states of the integral of the angular distribution over angles, is found to be in the form

where Q is the maximum exoergicity and positive. It is shown that, when adjusted to an experimental value, (σ_t) fits remarkably well the cross sections for the reaction K + CH₃I → Kl + CH₃, past the maximum of the cross sections reported by Gersch and Bernstein.     

Velocity dependence of the total cross section for helium-argon,neon-krypton and neon-xenon scattering

Velocity dependences of the total collision cross sections for scattering of helium by argon, neon by krypton and neon by xenon were measured using a time of flight method of velocity selection. For neon scattering glory oscillations were observed from which values of ?r_m (the product of the well depth and the internuclear separation at the minimum) were determined for various Lennard-Jones potentials. Comparison is made with the results from diffusion experiments and differential scattering measurements.     

Characterizing ion mobility and collision cross section of fatty acids using electrospray ion mobility mass spectrometry

This study investigated the ion mobility (IM) and the collision cross section (CCS) of fatty acids (FAs) using electrospray IM MS. The IM analysis of 18 FA ions showed intriguing differences among the saturated FAs, monounsaturated FAs, multi‐unsaturated FAs, and cis‐isomer/trans‐isomer with respect to the aliphatic tail chains. The length of aliphatic tail chain present in the ion structures had a strong influence on the differentiation of drift, while the number of double bond showed a weaker influence. The tiny drift differences between cis‐isomer and trans‐isomer were also observed. In the CCS measurements, two internal standards were involved in the mobility calibration and accuracy estimation. It insured our empirical CCS values were of high experimental precision (±0.35% or better) and accuracy (±0.25% or better). Moreover, the mass‐to‐charge ratio (m/z) – mobility plots obtained by ion mobility spectrometry with mass spectrometry analysis of FAs – was used to investigate the structural relationship between the molecules. Each series of FAs sharing a similar structure was aligned in the linear plot. Finally, the developed procedure was applied to the determination of FAs in rat adipose tissues, and it allowed the presence of 13 FAs to be confirmed with their exact masses and CCS values. These studies reveal the direct relationship between the behaviors in IM and the molecular structures and thus may provide further validations to the FA identification process. Copyright © 2015 John Wiley & Sons, Ltd.     

Differential photoionization cross section calculations for HI using the random-phase approximation with L2 basis functions

The photoionization cross sections and asymmetry parameters of the three main valence ionization processes in HI, corresponding to the formation of, respectively, 6π, 11σ, and 10σ holes, were calculated in the random-phase approximation (RPA). Our particular computational procedure, based on solving the integral equation for the half on the shell K-matrix upon a grid of points supplied by an L² basis set calculation, affords recovery of the electronic continuum degeneracy of the final states. This makes it possible to compute the differential ionization cross section at any energy up to the fourth ionization threshold, allowing for the interaction of the three channels considered. The total cross section obtained by applying the Stieltjes imaging procedure to the discrete spectrum yielded by the RPA is also reported. © 1996 John Wiley & Sons, Inc.