Figure 3.

Resonance Raman spectra of 2 prepared with ¹⁶O₂ (black) and ¹⁸O₂ (red) in 2-MeTHF at 110 K (λ_exc = 458 nm); difference spectrum (¹⁶O₂–¹⁸O₂) (green) and was multiplied by a factor 4 above 900 cm⁻¹ to better visualize the 1128-cm⁻¹ band and accompanying perturbations near 1064 cm⁻¹ where the ν(¹⁸O-¹⁸O) is expected to occur.