associated with the ionizations of the symmetric (ns,+ nsz) and antisymmetric (ns,-ns,) combinations are thus observed at 8.60 and 9.35 eV, respectively (the first one not very far from the corresponding one of 7 at 8.78 eV). On the other hand, the no lone pair ionization should be observed at the same energetic level in 7 and 8: 9.50 eV. The greater intensity of the 9.35-9.50-eV band of 8 is then accounted for by the attribution of two ionizations ...
[Maryanoff, Bruce E.; Greco, Michael N.; Zhang, Han-Cheng; Andrade-Gordon, Patricia; Kauffman, Jack A.; Nicolaou; Liu, Aijun; Brungs, Peter H. Journal of the American Chemical Society, 1995 , vol. 117, # 4 p. 1225 - 1239]