Reaction of Cu+ with dimethoxyethane: competition between association and multiple dissociation channels.

Abstract

The reaction of Cu+ with dimethoxyethane (DXE) is studied using kinetic-energy dependent guided ion beam mass spectrometry. The bimolecular reaction forms an associative Cu(+)(DXE) complex that is long-lived and dissociates into several competitive channels: C4H9O2(+)+CuH, Cu(+)(C3H6O)+CH3OH, back to reactants, and other minor channels. The kinetic-energy dependences of the cross sections for the three largest product channels are interpreted with several different models (including rigorous phase space theory) to yield 0 K bond energies after accounting for the effects of multiple ion-molecule collisions, internal energy of the reactant ions, Doppler broadening, and dissociation lifetimes. These values are compared with bond energies obtained from collision-induced dissociation (CID) studies of the Cu(+)(DXE) complex and found to be self-consistent. Although all models provide reasonable thermochemistry, phase space theory reproduces the details of the cross sections most accurately. We also examine the dynamics of this reaction using time-of-flight methods and a retarding potential analysis. This provides additional insight into the unimolecular decay of the long-lived Cu(+)(DXE) association complex. Comparison of results from this study with those from the complementary CID study, thus forming the same energized Cu(+)(DXE) complex in two distinct ways, allows an assessment of the models used to interpret CID thresholds.