Charge transfer reactions between gas-phase hydrated electrons, molecular oxygen and carbon dioxide at temperatures of 80–300 K

The recombination reactions of gas-phase hydrated electrons (H2O)n˙− with CO2 and O2, as well as the charge exchange reaction of CO2˙−(H2O)n with O2, were studied by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry in the temperature range T = 80–300 K. Comparison of the rate constants with collision models shows that CO2 reacts with 50% collision efficiency, while O2 reacts considerably slower. Nanocalorimetry yields internally consistent results for the three reactions. Converted to room temperature condensed phase, this yields hydration enthalpies of CO2˙− and O2˙−, ΔHhyd(CO2˙−) = −334 ± 44 kJ mol−1 and ΔHhyd(O2˙−) = −404 ± 28 kJ mol−1. Quantum chemical calculations show that the charge exchange reaction proceeds via a CO4˙− intermediate, which is consistent with a fully ergodic reaction and also with the small efficiency. Ab initio molecular dynamics simulations corroborate this picture and indicate that the CO4˙− intermediate has a lifetime significantly above the ps regime.