Figure 1: (a) Single differential cross sections (in the units of ) as a function of energy loss (= ), for the production of cations from electron impact ionization of at constant electron impact energy of 100 eV. (b) Same as (a) but at . (c) The solid lines show the trends of the calculated ratios of cross sections in Platzman plot in half energy range at 100 and 200 eV.