Calculations of Low Energy ElectronImpact Excitation Cross Sections of Diatomic Molecules by the CloseCoupling RMatrix and PolarizedOrbital Methods.
Abstract
Low energy electronimpact excitation cross sections of diatomic molecules are calculated by the closecoupling, Rmatrix, and polarizedorbital methods. The standard closecoupling procedure is generalized to the excitation of the a('1)(PI)(,g) state of N(,2) in the energy range 12.550.0 eV. The target wave functions are calculated by the molecular selfconsistentfield method using 10 stype and 6 ptype Gaussian orbitals as basis functions. The calculation is ab initio and exact within the limits of twostate closecoupling. The calculated cross sections agree well with experiments above 30 eV but can be improved below 30 eV by including the induced dipole polarization of the target. Two improvements to the standard close coupling are presented. A merger of the closecoupling and Rmatrix procedures yields an efficient technique for solving the scattering equations. Approximate closecoupling solutions are used as the basis for a Rmatrix calculation within a sphere of radius a centered on the molecule. The Rmatrix is then used as the boundary condition to integrate the scattering equations with the shortrange exchange terms omitted in the region r > a. Cross sections for the excitation of the b('3)(SIGMA)(,u)('+) state of H(,2) calculated by this method are presented. Comparison with the standard closecoupling calculation on the same state shows agreement within 5% with a factor of five reduction in the computing time. The basis set consisted of only two or three basis functions per channel, which is a markedly smaller set than typically employed in Rmatrix calculations. The second improvement is the inclusion of the induced dipole polarization of the target molecule. The polarizedorbital method is applied to the excitation of the B('1)(SIGMA)(,u)('+) state of H(,2). Firstorder adiabatic corrections to the molecular orbitals are generated, which yield the isotropic dipole polarizability of the ground state to within 8%. The ab initio longrange polarization potential constructed from these orbitals is included in the usual closecoupling procedure. The cross section is increased dramatically in the low energy peak region.
 Publication:

Ph.D. Thesis
 Pub Date:
 March 1982
 Bibcode:
 1982PhDT........62H
 Keywords:

 Physics: Molecular