The QB program: analysing resonances using R-matrix theory

A procedure for analysing resonances in atomic and molecular collision theo ry is programmed, which exploits the analytic properties of R-matrix theory to obtain the energy derivative of the reactance (K) matrix. This procedur e is based on the QB method (J. Phys. B 29 (1996) 4529) which defines matri ces Q and B in terms of asymptotic solutions, the R-matrix and energy deriv atives, such that dK/dE = B(-1)Q, from which eigenphase gradients of the K matrix can be obtained. Resonance positions are defined at the points of ma ximum gradient; resonance widths are related to the inverse of the eigenpha se gradients; resonance identifications are estimated from outer region sol utions. The program is tested on the twenty lowest Be-like Ne resonances 1s (2)2P(1/2,3/2)nl J = 1 degrees (n less than or equal to 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-fil e' in the format defined by RMATRX1 (Comput. Phys. Commun. 92 (1995) 290). (C) 1998 Published by Elsevier Science B.V.