HOW LARGE ARE HIGH-MOLECULAR RYDBERG STATES - A DIRECT EXPERIMENTAL TEST

Results of a three-laser experiment that probes the yield of charge transfer between high Rydberg states of C6H6 and C6D6+ are discussed in light of theoretical considerations. The primary observation is the rather low fraction of the long-living Rydberg states that do undergo such an electron transfer under realistic experimental conditions. A careful determination of the yield as a function of the energy of the Rydberg state and a determination of the absolute number of C6D6+ ions present in the focal volume enable the absolute cross section for this transfer to be determined as a function of the principal quantum number n of the Rydberg state. The experimental result is sigma = (26 +/- 6)n(4) (au)(2) vs the value of sigma = 20n(4) (au)(2) derived on the basis of physical considerations. This cross section is larger than the geometric size of the Rydberg orbit, and the reasons for this are discussed in detail. It is also argued that for high Rydberg states charge transfer is the dominant mechanism for the binary destruction of high Rydberg states. Despite the enormous cross section, the yield of the transfer can be made to be negligible under realistic experimental conditions, at typical ion densities.