Chemielectron and chemiion spectra have been recorded for the reaction of oxygen atoms with 2-butyne. Two chemielectron bands have been observed with band maxima at 0.06 +/- 0.04 and 0.27 +/- 0.06 eV whose relative intensity depends on the relative partial pressure of the reactants used. The chemiion spectra show that HCO+ and CH3CO+ are primary ions, although the relative intensity of the ion signals is affected by ion-molecule reactions in the reaction cell sed. The experimental evidence suggests that the two chemielectron bands can be assigned to the associative ionization reactions O + CH(X(+)II) --> HCO+ + e(-) and O + CH3C --> CH3CO+ + e(-). It is not possible to determine conclusively the electronic state of CH3C involved in the O + CH3C chemiionization reaction, although some evidence is presented that indicates that the CH3C((a) over tilde(4)A(2)) + O(P-3) reaction gives rise to the 0.27-eV chemielectron band.