Effect of van der Waals molecules on thermal electron attachment in some O2–hydrocarbon mixtures

Thermal electron attachment in O2–M(M; C2H6, C3H8 and n-C4H10) mixtures has been investigated using a microwave conductivity technique combined with x-ray pulse radiolysis. Evidence is presented for predominant electron attachment to van der Waals molecules (O2⋅M) at higher pressures. The rate constant of electron attachment to (O2⋅M) is much larger than that to O2 itself. A discrepancy between our previous results at lower pressures and swarm experiment results at higher pressures is explained quantitatively by the van der Waals molecule mechanism.