Figure 1.

Left: electronic spectra of 1 (dashed line) and 3 (solid line) in MeCN. Right: resonance Raman spectra (λ_ex = 407 nm) of ¹⁶O-3 (solid line) and ¹⁸O-3 (dashed line) recorded in frozen solution with samples mounted on a brass cold finger. Asterisks designate features from the CH₃CN solvent. The Raman samples were prepared by reaction of a 10 mM solution of 2(OTf)₂ in acetonitrile with 2 equiv. of PhI(OAc)₂, in the presence of 100 equivalents of H₂¹⁶O and H₂¹⁸O, respectively.