Excitation-ionization of helium to He+(n=2) at 365.8 eV

A second Born calculation of the (e, 2e) triple differential cross section for excitation-ionization of helium to He+ (n = 2) in coplanar asymmetric g eometry is found to be in excellent agreement with recent (relative) measur ements of Rouvellou et al (Rouvellou B, Rioual S, Pochat A, Tweed R J, Lang lois J, Nguyen Vien G and Robaux O 2000 J. Phys. B: At. Mel. Opt. Phys. 33 L599). The second Born cross section is very much larger by about a factor of four, than the corresponding first Born cross section, a trend that is c onsistent with absolute total cross section measurements for ionization to He+(2p) at the same impact energy.