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Rovibrational Spectral Analysis of CO3 and C2O3: Potential Sources for O2 Observed in Comet 67P/Churyumov–Gerasimenko

The recent ROSETTA mission to comet 67P/Churyumov–Gerasimenko detected surprisingly high levels of molecular oxygen (O2; hypervolatile species) in the coma. Current models predict that considerable levels of other hypervolatiles (such as molecular nitrogen, N2, methane, CH4, and Argon) should be found at similar levels, whereas they are more depleted. One explanation explored here is that larger (less volatile) parent molecules may have been formed during radiolysis of cometary ices and, upon sublimation, are subsequently broken down within the coma into smaller, more volatile fragments. In support of this hypothesis, this work employs reliable quantum chemical techniques to provide the spectral data necessary for the detection of two candidate precursor “parent” molecules, cyclic carbon trioxide (c-CO3), and cyclic dicarbon trioxide (c-C2O3). Benchmark computations performed for gas-phase CO2 give vibrational frequencies to within 1.5 cm−1 or better for the three fundamentals. Both c-CO3 and c-C2O3 have strong infrared features in the 4.5–5.5 μm (1800–2200 cm−1) range and other notable infrared features closer to 1100 cm−1 (9.10 μm). These molecules are both rotationally active, unlike CO2, and are therefore potentially observable and present new targets for radio telescope observations. Due to the stronger dipole moment, c-CO3 should be more easily detectable than the nearly non-polar c-C2O3. These data may help observations of these molecules and can provide insights as to how radiation-driven derivatization of CO/CO2 precursors could contribute to the generation of higher-mass parent species that subsequently degrade to produce more volatile species, such as O2, observed in cometary comae.