New and Old Measurements of Electron Scattering in Atomic Hydrogen

Abstract

A critical look is made of discrepancies and agreements between new and old measurements and theories for elastic and n = 2 excitation of atomic hydrogen by electron impact, mainly at 16·5, 54 and 100 eV. A discussion of earlier work indicates the contributions of Weigold and colleagues. The diffculties of observing and modelling small scattered fluxes at backward scattering angles and of making absolute cross section calibrations are noted. New measurements of elastic scattering at 16·5 eV confirm earlier measured angular distributions. An absolute calibration of the differential cross section at 16·5 eV gives agreement within one standard deviation with intermediate energy R-matrix and multi-pseudostate close coupling values. At 16·5 eV, measurements of the separate 2s and 2p differential cross sections and the lambda, R and I correlation parameters again support the values from those theories.