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Threshold collision-induced dissociation of Na + (L) with xenon is studied using guided ion beam mass spectrometry. The ligand L includes ethene, benzene, phenol, ammonia, acetaldehyde, acetone, and N,Ndimethylformamide. In all cases, the primary product formed corresponds to endothermic loss of the neutral ligand and the only other product observed is the result of ligand exchange processes to form NaXe + . The cross-section thresholds are interpreted to yield 0 and 298 K bond energies for Na + -L after accounting for the effects of multiple ion-molecule collisions, internal energy of the reactant ions, and dissociation lifetimes. Ab initio calculations at several levels of theory compare favorably to the experimentally determined bond energies for these and previously studied systems, L ) Ar, CO, dimethyl ether, H 2 O, methylamine, imidazole, dimethoxyethane, and several alcohols. Combined, these ligands cover a very wide range in binding energies, and thereby help to establish an absolute scale for sodium cation affinities.

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Collision-induced dissociation of (R1OH)Li+(R2OH) with xenon is studied using guided ion beam mass spectrometry. R1OH and R2OH include the following molecules: water, methanol, ethanol, 1-propanol, 2-propanol, and 1-butanol. In all cases, the primary products formed correspond to endothermic loss of one of the neutral alcohols, with minor products that include those formed by ligand exchange and loss of both ligands. The cross-section thresholds are interpreted to yield 0 and 298 K bond energies for (R1OH)Li+–R2OH and relative Li+ binding affinities of the R1OH and R2OH ligands after accounting for the effects of multiple ion–molecule collisions, internal energy of the reactant ions, and dissociation lifetimes. We introduce a means to simultaneously analyze the cross sections for these competitive dissociations using statistical theories to predict the energy dependent branching ratio. Thermochemistry in good agreement with previous work is obtained in all cases. In essence, this statistical approach provides a detailed means of correcting for the “competitive shift” inherent in multichannel processes.

The low energy collision-induced dissociation (CID) of Cr(CO)6+ with Xe is investigated using a recently modified guided ion beam tandem mass spectrometer, in the energy range from 0 to 5 eV in the center-of-mass (CM) frame. The additions to the instrument, updated with a double octopole system, and the new experimental methods available are described in detail. Integral cross sections for product formation are presented and analyzed using our standard modeling procedure. A slightly revised value for the bond dissociation energy of (CO)5Cr+–CO of 1.43±0.09 eV is obtained, in very good agreement with literature values. Axial and radial velocity distributions for primary and product ions are measured at 1.3, 2.0, and 2.7 eV, in the threshold region for product formation. The resulting velocity scattering maps are presented and discussed. Evidence of efficient energy transfer is observed from angular scattering of CID products. Experimental distributions of residual kinetic energies are derived and extend to zero, the point of 100% energy deposition. This indicates that energy transfer is nonimpulsive and probably associated with transient complex formation. For the first time, the experimental residual kinetic energy distributions are compared with the predictions of the empirical model used in integral cross section analyses. Good agreement is observed within experimental uncertainties. A model for the distribution of deposited energy during collisional activation is derived on the basis of these experimental observations.