Experimental observation of neutral radical formation from CH4 by electron impact in the threshold region

An apparatus combining the cross-beam and threshold-ionization techniques has been used to measure absolute cross sections for electron impact dissociation of CH4 molecules into the CH3 neutral radicals at energies from threshold up to 13 eV. The threshold energy for the lowest-lying 3T2 state has been observed to be 7.5 ±0.3 eV, and attributed to neutral CH3 formation. Peaks have been observed at ∼9.6 and 11.5 eV, in agreement with electronic excitation and photon impact neutral dissociation literature data. The current results indicate that all excited states of CH4 predominantly result in dissociation via the CH3 neutral radical channel below 12.5 eV