Eb. Gallogly et al., ELECTRON-IMPACT EXCITATION OF DELAYED IONIZATION OF C60 - EVIDENCE FOR RYDBERG STATES, Journal of physical chemistry, 98(12), 1994, pp. 3121-3125
A supersonic molecular beam apparatus with a quadrupole mass spectrome
ter has been used to study the delayed ionization of C60 by electron i
mpact. Time-of-flight (TOF) analysis through the quadrupole is used to
separate the direct ionization of C60 from delayed ionization. The ex
citation function for this delayed ionization has been measured as a f
unction of electron energy. The threshold for the excitation function
is 32 eV, with a peak at 46 eV and a full width at half-maximum of onl
y 15 eV. It is suggested that the excitation function is closely relat
ed to the cross section and that the shape of this function indicates
a forbidden transition may be excited. The relative magnitudes of the
delayed ionization signals are almost independent of the mass setting
of the quadrupole which has been used to suggest that most of the dela
yed ionization signal results from field ionization of a long-lived Ry
dberg state from C60.