Isotope effect in superconductingRb3C60

Measurements of the superconducting ${\mathit{T}}_{\mathit{c}}$ and Raman spectra in isotopically modified ${\mathrm{Rb}}_{3}$${\mathrm{C}}_{60}$ are reported. A decrease in ${\mathit{T}}_{\mathit{c}}$ of 0.65\ifmmode\pm\else\textpm\fi{}0.10 K in samples with (75\ifmmode\pm\else\textpm\fi{}5)% substitution of $^{13}\mathrm{C}$ for $^{12}\mathrm{C}$ yields an exponent of \ensuremath{\alpha}=0.37\ifmmode\pm\else\textpm\fi{}0.05. This interpreted as evidence for phonon-mediated pairing.