The reaction of CH3F with Au+ has been investigated at B3LYP and CCSD(T) levels. It was found that both C-F and C-H bonds can be activated by ground state Au+(S-1), whereas only C-H bond activation pathway was identified for excited state Au+(D-3). Among the possible product channels, the formation of AuCH2+ corresponding to HF-elimination is most favorable. Three reaction pathways were identified for HF-elimination. The energetically most favorable one undergoes through a mechanism of C-H bond activation -> C-F bond activation -> HF elimination. The activation barrier of this pathway is calculated to be small as 5.4 kJ/mol. The results of this study well rationalize the experimental observations. (C) 2008 Elsevier B.V. All rights reserved.