Near-Thermal Reactions of Au+(1S,3D) with CH3X (X = F,Cl)

Reactions of Au+(1S) and Au+(3D) with CH3F and CH3Cl have been carried out in a drift cell in He at a pressure of 3.5 Torr at both room temperature and reduced temperatures in order to explore the influence of the electronic state of the metal on reaction outcomes. State-specific product channels and overall two-body rate constants were identified using electronic state chromatography. These results indicate that Au+(1S) reacts to yield an association product in addition to AuCH2 + in parallel steps with both neutrals. Product distributions for association vs HX elimination were determined to be 79% association/21% HX elimination for X = F and 50% association/50% HX elimination when X = Cl. Reaction of Au+(3D) with CH3F also results in HF elimination, which in this case is thought to produce 3AuCH2 +. With CH3Cl, Au+(3D) reacts to form AuCH3 + and CH3Cl+ in parallel steps. An additional product channel initiated by Au+(3D) is also observed with both methyl halides, which yields CH2X+ as a higher-order product. Kinetic measurements indicate that the reaction efficiency for both Au+ states is significantly greater with CH3Cl than with CH3F. The observed two-body rate constant for depletion of Au+(1S) by CH3F represents less than 5% of the limiting rate constant predicted by the average dipole orientation model (ADO) at room temperature and 226 K, whereas CH3Cl reacts with Au+(1S) at the ADO limit at both room temperature and 218 K. Rate constants for depletion of Au+(3D) by CH3F and CH3Cl were measured at 226 and 218 K respectively, and indicate that Au+(3D) is consumed at approximately 2% of the ADO limit by CH3F and 69% of the ADO limit by CH3Cl. Product formation and overall efficiency for all four reactions are consistent with previous experimental results and available theoretical models.