The QB program: Analysing resonances using R-matrix theory

Abstract

A procedure for analysing resonances in atomic and molecular collision theory is programmed, which exploits the analytic properties of R-matrix theory to obtain the energy derivative of the reactance ( K) matrix. This procedure is based on the QB method (J. Phys. B 29 (1996) 4529) which defines matrices Q and B in terms of asymptotic solutions, the R-matrix and energy derivatives, such that d K/d E= B −1 Q, from which eigenphase gradients of the K matrix can be obtained. Resonance positions are defined at the points of maximum gradient; resonance widths are related to the inverse of the eigenphase gradients; resonance identifications are estimated from outer region solutions. The program is tested on the twenty lowest Be-like Ne resonances 1 s 22 P 1/2,3/2 nl J - 1° ( n ≤ 10). The test data is incorporated in the Fortran program, which can therefore be compiled and run as it stands; otherwise the program is designed for input of an ‘H-file’ in the format defined by RMATRX1 (Comput. Phys. Commun. 92 (1995) 290).