PNNL

Abstract

Because of its importance to so many processes, CO2 is one of the most studied molecules in science. However, we report here the discovery of a new phenomenon in the vibrational modes of supercritical CO2 upon isotopic labeling of both of its oxygens. The Raman spectrum of scC18O2 shows a transposition of the components of the Fermi dyad from their normal positions. Analysis from ab initio molecular dynamics studies shows a previously unknown quantum mechanical influence of the 18O on the extent of mixing of the two vibrational modes that give rise to the Fermi dyad. This discovery confirms the assignments of the modes comprising the Fermi dyad of scCO2 and provides the groundwork for further advances in vibrational spectroscopic studies on this important molecule.