A BBK-type theory for angular correlation parameters for electron-impact excitation of H(2p)

Considering the current interest in the BBK theory for ionization, a BBK-type theoretical model for direct excitation of hydrogen is discussed. To examine its applicability, the theory is applied to the 1s --> 2p excitation of hydrogen by electrons at 54.4 eV, and its predictions of the differential cross sections and angular correlation lambda and Ih parameters are compared with the results of other current theories. A most striking result is that in contrast to existing theories. the BBK-type model, for the first time, gives an excellent agreement with the experimental R parameter for larger scattering angles.