Present Integral Cross Sections Research Articles

Elastic scattering of electrons by barium atoms using the distorted wave method

Differential and integral cross sections of elastic scattering of electrons by barium atoms at intermediate energies (10 – 200 eV) were calculated using the distorted wave method. Being an elastic scattering both the initial and final distortion potentials were taken as the static potential of a barium atom in the initial state. The distorted waves are determined by the partial wave expansion method by expanding them in terms of spherical harmonics while the radial equation corresponding to distorted waves is evaluated using the Numerov method. A computer program DWBA1, for scattering was modified to perform numerical calculations for scattering and the results obtained are compared with the experimental and theoretical results available. The present integral cross sections are in good qualitative agreement with the experimental results and most of the theoretical results. For energies in the range 30 – 100 eV the present differential cross sections are in satisfactory agreement with the other theoretical and experimental results.

State-resolved quantum mechanical study of the intramolecular isotope effect in the C+ + HD reaction

Accurate quantum scattering dynamics calculations for the C+ + HD reactions on the ground 12A′ potential energy surface have been performed in the collision energy range of 0.05–1.0 eV. The present integral cross sections and branching ratios are compared with previous experimental and theoretical results. Both the CH+ and CD+ products are distributed in vibrational cold but rotational hot states. Total differential cross sections for both channels exhibit forward–backward symmetry. The state - resolved differential cross sections and the opacity functions show that the product rotational quantum numbers correlate strongly with the total angular momentum J.

Dynamics of H(2S) + CH(X2Π) reactions based on a new CH2() surface via extrapolation to the complete basis set limit

A grid of 5285 ab initio points is utilized to construct a 3D potential energy surface (PES) of the system. In the calculation procedure, the aug-cc-pVXZ (X = Q and 5) basis sets with Davidson correction are employed. The reference wave function for the multi-reference configuration interaction calculations is composed of a full valence complete-active-space self-consistent field wave function. In order to get a more accurate PES, the complete basis set (CBS) limit proposal and the many-body expansion form are used, with the total root mean square deviation of the final CBS-PES being 0.0349 eV. Based on the accurate CBS-PES, the stationary points and vibrational energy levels are obtained and examined in detail, which agree well with other theoretical results. Then, utilizing the CBS-PES and quasi-classical trajectory method, the integral cross-sections (ICSs) and rate constants of the → / reactions are calculated. It is found that the present ICSs are in good agreement with other theoretical results, and is the major product channel. For this channel, the rate constants calculated in this work agree well with experimental and other theoretical results in the high-temperature range. It is worth noting that at room temperature, the theoretical results, including the present work, are consistent with each other, but they are all higher (about 7–10 times) than the experimental result, which implies that a new measurement for the rate constant at room temperature is necessary.

Quasiclassical trajectory study of the C(¹D) + H₂ → CH + H reaction on a new global ab initio potential energy surface.

Quasiclassical trajectory (QCT) calculations have been performed on a new global ab initio potential energy surface (PES) for the singlet ground state (1(1)A') of the CH2 reactive system. Our new PES can give a very good description of the well and asymptote regions, and particularly regions around conical intersections (CIs) and of van der Waals (vdW) interactions. The integral cross sections, differential cross sections, and product rovibrational state distributions for the C((1)D) + H2 → CH + H reaction have been investigated in a wide range of collision energies. The present integral cross sections are much larger than the previous QCT results at low collision energies, which can be attributed to the differences of the PESs in the regions around the CIs and vdW complexes. The thermal rate coefficients in the temperature range 200-1500 K have also been calculated and very good agreement with experiment is obtained.

Benchmark Integral Cross Sections for Electron Impact Excitation of the n = 2 States in Helium

In this paper, we present integral cross sections (ICS) for electron impact excitation of the n = 2 levels in helium in the impact energy range of 23.5 eV to 35 eV. The ICS of each final state, 23S, 21S, 23P and 21P, has been determined by integration of the angular differential cross sections (DCS) over all of 0° to 180°, where those DCS were obtained from both our previous experiments and the extrapolation using the convergent close coupling calculation. The present experimental ICS for the optically allowed 21P transition state are also compared with those obtained from the BEf-scaling method. Very good agreement between the experimental and BEf-scaled 21P ICSs is generally found in the measured impact energy region.

Low-energy total electron scattering in the methyl halides CH3Cl, CH3Br and CH3I

Absolute integral and backward total scattering cross-sections are reported for the polar molecules CH3Cl, CH3Br and CH3I at electron energies from ∼10meV to 0.7eV for backward scattering and 20meV to 9.5eV for integral scattering. Below 1–2eV, the present integral cross-sections are significantly higher than data in the literature. The Born point-dipole cross-sections for rotationally inelastic scattering have been calculated and are compared with the experimental total scattering cross-sections. Discrepancies give a measure of pure elastic scattering at very low energy. Data for CH3I demonstrate the presence of strong resonant elastic scattering and dissociative attachment at low energy.

Oscillator strengths and electron-excitation cross sections for atomic nitrogen

The $\mathrm{LS}$ states belonging to the configurations ${2s}^{2}{2p}^{3},$ ${2s2p}^{4},$ ${2s}^{2}{2p}^{2}3s,$ ${2s}^{2}{2p}^{2}3p,$ ${2s}^{2}{2p}^{2}3d$, and ${2s}^{2}{2p}^{2}4s$ of neutral nitrogen are considered in the calculations of excitation energies and oscillator strengths. Extensive configuration interaction wave functions are used, which give excitation energies in close agreement with the experiment. The calculation of the differential and integral cross sections of the forbidden ${}^{4}{S}^{o}{\ensuremath{-}}^{2}{D}^{o}$ transition for the scattering of electrons from atomic nitrogen is performed in a 11-state close-coupling approximation using the R-matrix method in the energy region from threshold to 70 eV. The calculated differential cross sections are peaked in the backward direction and compare very well with the recent measurement. The present integral cross sections also show very good agreement with the available other calculations and measurement.