Muonium atom spin exchange with alkali-metal vapors : Mu+Cs

The thermally averaged total electron spin-flip cross sections ([sigma][sub SF]) for Mu-Cs have been measured in a 2 atm N[sub 2] moderator at 543, 566, and 643 K using the muon-spin-rotation technique. Within an overall experimental error of [plus minus]15%, the measured cross sections can be taken as temperature independent, [sigma][sub SF]=39.7[plus minus]6.0[times]10[sup [minus]16] cm[sup 2], though there may be a trend to decreased values at the lower temperatures. This average value is considerably lower than either the early calculated results of Dalgarno and Rudge [Proc. R. Soc. London Ser. A 286, 519 (1965)] or the more recent ones of Cole and Olson [Phys. Rev. A 31, 2137 (1985)] for the corresponding H-Cs collisions, indicating a dramatic isotope effect.