Low-energy (<1 eV) electron attachment to molecules in very-high pressure gases: C6H6

Benzene has been found to capture slow (≲ 0.3 eV) electrons in high densities of N2 (and Ar) with a rate that increases with increasing N2 density and decreasing electron energy at near-thermal energies. The dependence of the attachment rate on the N2 density and the electron energy has been studied in detail, and a model is presented that accounts for the experimental results. On the basis of this model the autodetachment lifetime of C6H6-* has been estimated and found to vary from ∼1 psec at 0.04 eV to ∼0.2 psec at 0.18 eV. From the high-pressure experiments the ``liquid state behavior'' has been predicted also. The finding that benzene negative ions are formed in the gas phase forces the conclusion that the benzene molecule has a positive (>0 eV) electron affinity, (EA)B, contrary to the accepted view that (EA)B <0 eV. The short autodetachment lifetime of C6H6-*, however, indicates that (EA)B is small. Benzene was also studied in mixtures with C2H4 and C2H4–N2. The results of these latter experiments strongly indicated that the probability of electron detachment in C6H6-*-C2H4 collisions is large.