Experimental study of the reaction of O− ions with CO2 molecules with different ternary gases at temperatures relevant to the martian ionosphere

The reaction of oxygen anions with carbon dioxide molecules is considered to be the main channel of CO3− ion formation in the Martian ionosphere. Comprehensive theoretical ion-chemical models of the Martian ionosphere require experimental data on the reactivity of negative ions with neutral gases under relevant ambient temperature and pressure conditions. The temperature dependence of the rate of the ternary reaction of O− with CO2 has been measured at temperatures relevant to the ionosphere of Mars using a VT-SIFT instrument using both helium and nitrogen as the carrier (ternary) gases. The ternary rate coefficient of the reaction was measured equal to (1.24 ± 0.06) × 10−28 (300/T)2.86±0.28 and (2.29 ± 0.05) × 10−28 (300/T)2.06±0.13 cm6s−1 for He and N2 carrier gas, respectively, in the temperature range of 230–340 K. The k3 is over two times higher in nitrogen than in helium and has a less strong inverse temperature dependence.