Extension of the Burgess-Tully method to fit neutral atom and molecule cross-sections

¹ University of Strathclyde, 107 Rottenrow, Glasgow G4 0NG, UK
² National Institute for Fusion Science, Toki, Gifu, 509-5292, Japan

Send offprint request to: H.P. Summers

Received: 15 February 2000
Accepted: 27 March 2000

Abstract


The method introduced by Burgess & Tully (1992) for the examination and compacting of collision cross-section data for ions is extended to neutral atoms and molecules. To give adequate weighting and critical focus to the threshold region, as Burgess & Tully did for the high energy asymptotic region, the energy and collision strength transformations have been modified. The new mapping is to the interval [ -1, 1] , with the excitation threshold region up to some switching energy mapped to [ -1, 0] . The high energy asymptotic region above the switching energy is mapped to the interval [0, 1]. A nine-point spline of equally spaced knots replaces the Burgess-Tully five-point spline. Appropriate threshold functional forms are incorporated into the description and the whole examination and fitting procedure is implemented as an interactive graphical utility under IDL that is available as a “stand-alone” code.