Determination of mean collision cross sections of free radical OH with foreign gases

Experimental studies of absorption by the free radical OH in the 13.4 GHz region (2Π^{$\text{3}\text{2}$} state, J = $\text{7}\text{2}$) have been used to determine collision cross sections of OH with foreign gases. We have performed both direct measurements of linewidths and measurements of absorption saturation over wide pressure ranges. The experimental values are compared with available theoretical values.     

Electron-exciton inelastic collision cross sections for different semiconductors

The electron-exciton inelastic collision cross sections for the different semiconductors CdS, ZnO, CdSe, Si, Cu₂O, CuCl, CuBr and CuI have been calculated in the Glauber approximation. The transitions 1s–2s, 1s–3s, 1s–2p and 1s–3p have been considered. The calculations are carried out as function of the different available values of $\text{σ =}\text{m}{}^1{}_{\mathrm{e}}\text{m}{}^1{}_{\mathrm{h}}$ where m¹_e and m¹_h are, respectively, the electron a corresponding semiconductors.     

Double charge transfer cross sections in collision of protons with helium atom

Theoretical total cross sections for the double charge transfer in proton-helium collisions are analysed using the four-body boundary corrected continuum intermediate state approximation in the energy range of 30 to 500 keV. We have also obtained differential double capture cross sections as a functions of projectile scattering angle. The intermediate continuum state of each of the active electron has been taken into account in this formalism. Our calculated results are compared with the previous experimental and theoretical values. The agreement is very encouraging.     

Disorientation and disalignment cross sections of excited Rb-atoms colliding with noble gases

The disorientation and disalignment cross sections for the depolarization of Rb 5²P_1/2 and 5²P_3/2 states due to collisions with the inert gases He, Ne, Ar, Kr, Xe were measured at a temperature of 317 K. The experiments were done in a static magnetic field H₀ which served to decouple the nuclear spin. Unpolarized Rb-D₂-radiation was made incident on the Rb-vapour parallel to H₀ thus generating an alignment in the²P_3/2-state. The linear polarization of the fluorescent D₂-light emitted at right angles towards the incident light beam was measured as a function of the rare gas pressure (0... 3 Torr). Similarly, for the disorientation measurements the vapour was excited by circularly polarized D₂- or D₁-radiation parallel to H₀ and circularly polarized fluorescent light was observed at small angles towards the backward direction. From the decrease of the polarizations observed at rising pressure the cross sections were determined. The comparison with theoretical results gives satisfactory agreement.     

Calculation of cross sections for elastic electron-molecule collisions

The phase functions and the partial and total elastic scattering cross sections for electrons with energies from 0.23 to 14.46 eV are numerically calculated on a computer for nitrogen and oxygen molecules. The phase equation in spheroidal coordinates is employed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 104–107, May, 1976.     

Calculation of the ratio of isomeric cross sections

A new, more rigorous method for calculating the ratio of isomeric cross sections has been developed. The method is particularly valuable when the energy and spin distribution are known before the gamma rays populating the isomeric and ground states start to cascade. The usefulness of the method was demonstrated by applying it to the analysis of the ratio of isomeric cross sections in the ¹⁹⁶Hg(n,γ)¹⁹⁷Hg reaction, which was initiated by thermal neutrons.     

On the determination of collision cross sections by nuclear Doppler shift

We report on measurements of the energy loss of ions in matter by “Inverted Doppler Shift Attenuation” (IDSA). This new method is an inversion of the “Doppler Shift Attenuation” (DSA) method for the determination of lifetimes of nuclear states. While in DSA the exact knowledge of the velocity dependent energy loss functiondE/ds is required, it is shown that in IDSA this function or the absolute collision cross section, respectively, can be determined from the Doppler spectrum of an excited nuclear fragment recoiling in matter, whose lifetime is known. No corrections or assumptions concerning the collision processes are necessary. ⁷Li^* fragments (E _γ=478 keV) from the¹⁰B(n, α)⁷Li^* reaction produce an easily observable and analysable Doppler spectrum. Here boron must be a constituent or an implanted impurity of the material to be investigated. The experimental set-up is described. An exact relativistic analysis of the Doppler spectrum is given. The measured collision cross sections turn out (a) to be proportional tov within the range 1.5 · 10⁸≦v≦4.8 · 10⁸ cm/sec, (b) are thus only due to pure “electronic” collisions, and (c) sensitively dependent on the charge distributions of the target atoms.     

He-NO碰撞体系分波截面的理论计算

首先用Huxley势函数拟合在RCCSD(T)/aug-cc-pVTZ bf理论水平下计算的He-NO相互作用能数据,从而得到了He原子与NO分子相互作用各向异性势;然后用密耦近似方法计算了He-NO碰撞体系的总分波截面、弹性分波截面和非弹性分波截面,并总结了分波截面的变化规律.计算结果表明,拟合势较好地描述了He-NO系统相互作用的各向异性特征,利用碰撞体系分子间势的量子化学从头计算结果,可解决势能参数难以确定的问题,对进一步研究原子与分子碰撞机理有一定参考价值.     

Absolute OH absorption cross sections (for lidar measurements)

Absorption cross sections are important in quantitative optical measurements of OH. We have used existing experimental data to calculate the effective cross sections for a number of transitions in the A-X system of OH, taking into account such factors as temperature and the spectral shape and width of both the absorption line and the excitation source. Details of the calculations are presented to allow easy extension to other transitions.     

Electron scattering cross sections with HF,OH, NH and CH molecules

Total cross sections including elastic scattering, electronic excitation-ionisation and the dipole rotational excitation are calculated for electron impact on HF, OH, NH, and CH molecules. The additivity rules as well as single-centre expansion are employed for this purpose. A comparison was possible for the e-HF system only. Our results are expected to be good at intermediate to high energies (> 50 eV).     

He-N2碰撞体系散射截面的理论研究

本文运用量子化学从头计算MP2方法6-311 G(3df,2p)基组,计算了He-N2相互作用的势能,拟合出He原子与N2分子相互作用的各向异性势函数,其势函数参数:势能球平均势阱位置、势阱深度、势能零点位置与通过散射实验数据分析的ESMSV(Exponential-Spline-Morse-Spline-Van der waals)势比较吻合.然后,用公认精确度高的密耦方法计算了He原子与N2分子碰撞体系的总微分截面、弹性微分截面、转动激发的非弹性微分截面和积分截面,计算结果与实验数据符合得较好.     

Calculation of multiple-excitation cross sections using angle-dependent phase shifts

Multiple-excitation cross sections for the scattering of 70.4 MeV ¹²C ions on the even neodymium isotopes are calculated by the method of angle-dependent phase shifts. The results are compared with the data.     

Negative ion clusters in oxygen: collision cross sections and transport coefficients

Using a pulsed Townsend experiment, we have observed the formation of two negative ion species in oxygen over the pressure range 100–600 torr, and the density-normalised electric field strength, E/N, from 2 to 14 Td. The peculiar shape of these transients has led us to propose a scheme of three-body ion-molecule reactions leading to the formation of O₄ ^- and O₆ ^-, which is substantiated by a curve fitting procedure. The resulting mobility data of these two ionic species have been used to calculate their respective momentum transfer collision cross sections, together with the dissociation cross sections that are needed to extend the range of calculation of mobility and diffusion (transverse and longitudinal) to 1000 Td. These calculations were based on an optimised Monte Carlo algorithm, using collision cross sections obtained from a JWKB approximation (Jeffreys-Wentzel-Kramers-Brillouin) or taken from literature.     

Absolute electron scattering cross sections for the CF2 radical

Using a crossed electron-molecular beam experiment, featuring a skimmed nozzle beam with pyrolytic radical production, absolute elastic cross sections for electron scattering from the CF2 molecule have been measured. A new technique for placing measured cross sections on an absolute scale is used for molecular beams produced as skimmed supersonic jets. Absolute differential cross sections for CF2 are reported for incident electron energies of 30-50 eV and over an angular range of 20-135 deg. Integral cross sections are subsequently derived from those data. The present data are compared to new theoretical predictions for the differential and integral scattering cross sections, as calculated with the Schwinger multichannel variational method using the static-exchange and static-exchange plus polarization approximations.     

Calculation of photoionization cross sections by the absorbing boundary method

A new method for the calculation of quantum state decay rates, the absorbing boundary method (ABM), has recently been developed. In this talk the general form of the ABM will be outlined. The pseudo bound state approach to the calculation of continuum rates such as photoionization cross sections and used by Langhoff and coworkers will be briefly reviewed and shown to lack precision in the absence of information about the line widths and shapes of the pseudo bound states. It will then be noted that the ABM can be used to construct a rigorous new approach to the calculation of photoionization cross sections incorporating the necessary lifetime information for the pseudo bound states while still allowing the computation to be carried out by bound state procedures.     

Calculation of the photoionization with deexcitation cross sections of He and helium-like ions

We discuss the results of the calculation of the photoionization with deexcitation of excited He and helium-like ions Li⁺ and B³⁺ at high but nonrelativistic photon energies θ. Several lower ¹ S and ³ S states are considered. We present and analyze the ratios R _d ⁺ * of the cross sections of photoionization with deexcitation, σ _(d) ⁺ *(θ), and of the photoionization with excitation, σ⁺*(θ). The dependence of R _d ⁺ * on the excitation of the target object and the charge of its nucleus is presented. In addition to theoretical interest, the results obtained can be verified using long-lived excited states such as 2³ S of He. The text was submitted by authors in English.     

碰撞能量对He-N2的散射截面的影响

用密耦近似方法计算了He和N2体系的微分截面和总截面及转动激发分波截面,得出微分截面及总截面随入射能量变化的规律.     

Phase space manipulation of cold free radical OH molecules

We report bunching, slowing, and acceleration of a supersonically cooled beam of diatomic hydroxyl radicals (OH). In situ observation of laser-induced fluorescence along the beam propagation path allows for detailed characterization of longitudinal phase-space manipulation of OH molecules through the Stark effect by precisely sequenced inhomogeneous electric fields.