[en] In recent years there has been growing interest in the dynamics of collisions between Rydberg atoms and molecules. The authors have recently studied the formation of negative ions following collisions between cesium atoms in selected ns and nd Rydberg states (n = 13-29) and carbon disulfide molecules. For a narrow range of effective principal quantum number near n* = 17, rates for CS₂^- formation are found to be isotope-dependent, with the rate constant for C³²S³⁴S^- being up to 4.5 times larger than that for C³²S³²S^-. Details of the experimental techniques and results will be presented along with possible explanations for the observed isotope dependence and plans for future study