Rate coefficient of CO₂ splitting in recombining H₂ and He plasmas with ultralow electron temperatures

We investigated CO₂ splitting in recombining H₂ and He plasmas with ultralow electron temperatures between 0.1 and 0.4 eV. The conversion from CO₂ to CO and O₂ was observed in the ultralow-temperature plasmas. Since the rate coefficients of dissociation of CO₂ via electronic excited states are negligible at the ultralow electron temperature, the present experimental result gives us corroborative evidence of the CO₂ splitting via vibrational excited states. The rate coefficient of the CO₂ splitting, which was evaluated from the temporal variation of the CO₂ density, decreased clearly with the electron temperature. In addition, the rate coefficient observed in the ionizing H₂ plasma with an electron temperature of 4 eV was one order of magnitude smaller than that observed in the recombining plasmas. It has been shown that the CO₂ splitting via vibrational excited states has a larger rate coefficient than that via electronic excited states. (paper)