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

Reactions of Cu-2 with several small molecules have been studied in th e gas phase, under thermalized conditions at room temperature, in a fa st-flow reactor. They fall into one of two categories. Cu-2 does not r eact 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 ch aracteristic of association reactions. Second-order rate constants for all four of these reagents are dependent on total pressure. The react ions 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 fa ll-off behavior at pressures above 3 torr. Limiting low-pressure, thir d-order rate constants are 0.66 +/- 0.10, 8.8 +/- 1.2, 9.3 +/- 1.4, an d 85 +/- 15 x 10(-30) cm(6) s(-1) in He for CO, NH3, C2H4, and C3H6, r espectively. Modeling studies of these rate constants imply that the a ssociation 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 wit h Cu atoms, larger clusters, and surfaces. (C) 1994 John Wiley & Sons, Inc.