Neutral gold carbonyl clusters, Au(m)(CO)(n) (m = 3-9, n = 2-7, m > n), are generated by laser ablation of Au into a mixture of CO/He, cooled in a supersonic expansion, and reacted with O(2) and N(2)O in a fast flow reactor. The neutral reactants and products are detected in a time of flight mass spectrometer through single photon ionization by a 193 nm laser. Signal intensities of Au(3)(CO)(2,3), Au(5)(CO)(4), and Au(7)(CO)(4,5) decrease significantly following reaction of these clusters with O(2) in the fast flow reactor; only Au(3)(CO)(2) and Au(3)(CO)(3) signals decrease moderately following reaction with N(2)O. The reaction cross section for Aum(CO) n with N(2)O is significantly smaller than that with O(2). Density functional theory calculations with and without explicit consideration of relativistic effects are performed to investigate the reaction mechanisms for the oxidation of Au(3)(CO)(2) and Au(3)(CO)(3) clusters with O(2) and N(2)O. Both calculational algorithms predict a considerable barrier for the reactions of Au(3)(CO)(2,3) with N(2)O. Non relativistic density functional theory calculations predict a positive overall barrier for the reactions of Au(3)(CO)(2,3) with O(2), in disagreement with experimental observations. Relativistic density functional theory calculations for the reactions Au(3)(CO)(2,3) with O(2) predict that they are thermodynamically allowed, although the barrier heights are not in the appropriate order to support the apparent relative reactivities of Au(3)(CO)(2) and Au(3)(CO)(3) with O(2). (C) 2011 Elsevier B. V. All rights reserved.