In a previous communication we gave the assignment of a number of weak Q-branches that were observed in the rovibrational Raman spectrum of natural CO2. They were identified as such by the method of direct scanning of the purely isotropic part of Raman scattered light. Here we report Raman spectroscopic measurements of 99% enriched C18O2 in the Fermi resonance region. In addition to the strong Σ- and II-diads of this isotopic species, again some weak Q-branches could be detected and assigned to essentially the same transitions as in 12C16O2. Our experimental set-up has been described in detail elsewhere.
H. W. Klöckner, H. Finsterhölzl, K. Srinivasan, and H. W. Schrötter, "Raman Spectra of Carbon Dioxide and Its Isotopic Variants in the Fermi Resonance Region: II. 12C18O2," Appl. Spectrosc. 32, 401-402 (1978)