REACTIONS OF THE COPPER DIMER, CU-2, IN THE GAS-PHASE

Reactions of Cu-2 with several small molecules have been studied in the gas phase, under thermalized conditions at room temperature, in a fast-flow reactor. They fall into one of two categories. Cu-2 does not react with O-2, N2O, N-2, H-2, and CH4 at pressures up to 6 torr. This implies bimolecular rate constants of less than 5 x 10(-15) Cm-3 s(-1) at 6 torr He. Cu-2 reacts with CO, NH3, C2H4, and C3H6 in a manner characteristic of association reactions. Second-order rate constants for all four of these reagents are dependent on total pressure. The reactions with CO, NH3, and CzH4 are in their low pressure limit at up to 6 torr He buffer gas pressure. The reaction with C3H6 begins to show fall-off behavior at pressures above 3 torr. Limiting low-pressure, third-order rate constants are 0.66 +/- 0.10, 8.8 +/- 1.2, 9.3 +/- 1.4, and 85 +/- 15 x 10(-30) cm(6) s(-1) in He for CO, NH3, C2H4, and C3H6, respectively. Modeling studies of these rate constants imply that the association complexes are bound by at least 20 kcal mol(-1) in the case of C2H4 and C3H6 and at least 25 kcal mol(-1) in the other cases. The implications of these results for Cu-ligand bonding are developed in comparison with existing work on the interactions of these ligands with Cu atoms, larger clusters, and surfaces. (C) 1994 John Wiley & Sons, Inc.