Laboratory measurements of gas-phase reactions of polyatomic carbon ions C + n(n=1-6) and CnH + (n=2-5) with carbon monoxide

The selected-ion flow tube (SIFT) technique has been employed in the study of reactions of carbon monoxide with the polyatomic carbon cations C⁺_n(n=1-6) and C_nH⁺(n=2-5) at 296±2 K in helium buffer gas at ∼0.34 Torr and 1.1×10¹⁶ atoms cm^-3. The polyatomic carbon cations were generated by electron impact on a suitable parent molecule. Carbon monoxide was observed to add rapidly to C⁺_n(n=2-6) twice in succession to form polyatomic carbon monoxide and dioxide cations, and once to C_nH⁺ to form polyatomic carbon monoxide cations. Further additions did not occur with measurable specific rates. This remarkable behavior is attributed to double bond formation at the terminal carbon atoms of the polyatomic carbon cations. The specific rate for the addition of CO was observed to vary with the size of the polyatomic carbon cation, increasing to a maximum for reactions with five atoms in the reacting ion. This trend is attributed to an increase in the lifetime of the intermediate addition complex.