RYDBERG ELECTRON-TRANSFER TO C-60 AND C-70

Experimental results are reported for the attachment of Ar*(nl) Rydbe rg electrons to C-60 and C-70 over the range n = 19-270. In agreement with other Rydberg work we find that the rate coefficient for C-60(-) formation remains large (around 2 . 10(-8) cm(3) s(-1)) towards high n and is essentially constant for n > 40, thereby indicating the presen ce of an s-wave attachment process in contrast to interpretations of f ree electron attachment data postulating p-wave threshold behaviour. T he rate coefficients for C-70(-) formation show a similar n-dependence as those for C-60(-), but they are significantly larger. Possible mec hanisms for s-wave attachment including formation of polarization-boun d negative ion states are discussed. Regarding the threshold behaviour for the attachment of free electrons to C,, we propose - based on an analysis of available free electron data - the presence of an s-wave ( possibly resonance type) contribution near zero energy.