Cross Sections For Low-energy Collisions Research Articles

Relativistic calculations of the charge-transfer probabilities and cross sections for low-energy collisions of H-like ions with bare nuclei

A new method for solving the time-dependent two-center Dirac equation is developed. The time-dependent Dirac wave function is represented as a sum of atomic-like Dirac-Sturm orbitals, localized at the ions. The atomic orbitals are obtained by solving numerically the finite-difference one-center Dirac and Dirac-Sturm equations with the potential which is the sum of the exact reference-nucleus potential and a monopole-approximation potential from the other nucleus. An original procedure to calculate the two-center integrals with these orbitals is proposed. The approach is tested by calculations of the charge transfer and ionization cross sections for the H(1s)--proton collisions at proton energies from 1 keV to 100 keV. The obtained results are compared with related experimental and other theoretical data. To investigate the role of the relativistic effects, the charge transfer cross sections for the Ne^{9+}(1s)--Ne^{10+} (at energies from 0.1 to 10 MeV/u) and U^{91+}(1s)--U^{92+} (at energies from 6 to 10 MeV/u) collisions are calculated in both relativistic and nonrelativistic cases.

Classical evaluation of low energy collision cross sections

Numerical evaluations of ion - hydrogen atom collision's ionization cross sections with the Classical Trajectory Monte Carlo (CTMC) method are shown here to be valid in the keV energy region. Careful numerical integration of the Coulomb Three-Body (CTB) system's (A q+ , p + , e - ) classical trajectories is correctly assessing the « saddle electron » dynamics in the 1 to 10 keV energy region. Resulting ionization cross sections are comparable to those recently obtained experimentally, although they are still lower for the higher energies. Consequently, the method has be extended to calculate low energy hydrogen - hydrogen collision ionization processes, which have been measured recently.

Scattering cross sections for low-energy alkali cation +C60 collisions: The relevance of polarization

Total scattering cross sections for low-energy collisions of C60 fullerene with alkali ions are theoretically estimated using an accurate spherical potential approximation. These cross sections show the relevance of polarization effects. Our results indicate a way in which collisional experimental methods could be used to measure the high polarizabilities of C60 and other fullerenes.

Scattering of neutral metal clusters: Long-range interactions and response properties

The absolute integral cross sections for low-energy collisions of neutral sodium clusters Nan (n=2–40) with atoms and molecules (Ar, N2, O2, and halogens) have been measured. The cross sections are found to be exceptionally large (up to thousands of square angstroms), showing the dominant role of long-range intermolecular interactions. Elastic scattering proceeding under the influence of the van der Waals force, and a reaction channel involving electron transfer can successfully describe the measurements. The strength of the van der Waals potential is defined by such cluster response properties as the electric polarizability and the frequency of the giant dipole resonance. The reactive electron-jump channel, in turn, is described by the ‘‘harpooning’’ mechanism which is sensitive to the cluster ionization potential. Employing parameters taken from spectroscopic studies of alkali clusters, we obtain good agreement with the observed cross sections. This provides a direct connection between beam scattering experiments and studies of cluster electromagnetic response properties.

Elastic and reactive collisions of atoms and molecules with neutral alkali clusters

We have measured absolute integral cross sections for low-energy collisions of atoms and molecules with neutral sodium clusters over a wide cluster size range (n=2–40). The cross sections are exceptionally large, reaching values of thousands of square angstroms. Consequently, the scattering involves long-range interactions. The van der Waals force, acting either alone (Nan+N2) or in concert with the inelastic charge-transfer “harpooning” channel (Nan+Cl2, Nan+O2) can describe the measurements. Using interaction parameters taken from spectroscopic studies of alkali clusters, we find very good agreement with the data. This provides a point of contact between beam scattering experiments and studies of cluster electromagnetic response properties.

Low energy collision cross sections of H − and OH − ions in oxygen : C. E. Baker, et al., J. Chem. Phys., 37 (11), 1 Dec. 1962, 2571–2574

Low energy collision cross sections of H − and OH − ions in oxygen : C. E. Baker, et al., J. Chem. Phys., 37 (11), 1 Dec. 1962, 2571–2574