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Density functional theory (DFT) calculations have been carried out to explore the potential energy surface (PES) associated with the gas-phase reactions between ethylenediamine (En) and Cu + . The structures and bonding characteristics of the different stationary points of this PES have been investigated at the B3LYP/ 6-31 lG(d,p) level. Final energies were obtained by means of B3LYP/6-311+G(2df,2p) single point calculations. En strongly binds Cu + by forming a chelated structure in which the metal cation binds to both amino groups. Different mechanisms leading to the loss of H 2 , NH 3 , and CuH are analyzed in terms of the topology of the PES. The most favorable mechanism corresponds to the loss of H 2 , through a process in which the transition metal cation acts as a carrier, connecting a hydrogen atom from a methylene group with a hydrogen atom of one of the amino groups. The product ion is a five-membered ring in which Cu + bridges between N atoms of the H 2 N-CH 2 -CH-NH moiety. The loss of ammonia is less favorable, because all mechanisms involve higher activation barriers. The most favorable of these mechanisms implies hydrogen shift between the two methylene groups that triggers a spontaneous hydrogen shift between the two amino groups, favored by the existence of a strong intramolecular hydrogen bond. These mechanisms explain the experimental results involving fully C-deuterated species, where only a loss of HD and NH 3 are observed. The loss of HCu is also discussed.

The B3LYP density functional approach has been used to calculate the Cu+ binding energies of ethyl and vinyl amines, phosphines, and arsines. Geometries were fully optimized at the B3LYP/6-311G(d,p) level, and the final energies were obtained in B3LYP/6-311+G(2df,2p) single-point calculations. Significant differences between nitrogen-, phosphorus-, and arsenic-containing compounds have been found. For ethyl derivatives, the global minimum corresponds to the attachment of Cu+ to the heteroatom. However, whereas for P and As derivatives of agostic complexes in which the metal cation interacts with the hydrogen atoms of the XH2 or the CH2 groups are found to be stable, they are not for ethylamine. For vinylamine, attachment to Cβ is favored with respect to attachment to the heteroatom, whereas vinylphosphine and vinylarsine behave as P and As bases, respectively. The Cu+ basicity trends also differ from those found for the corresponding proton affinities. Thus, although ethylamine is more basic than ethylpho...

We have studied the structure of small doubly charged carbon clusters using density functional (DFT) and coupled-cluster (CC) theories. We have found that, with the exception of C42+ and C72+, the most stable geometry corresponds to linear structures of D∞h symmetry. This is at variance with the behavior observed in neutral and singly charged carbon clusters. We have also evaluated dissociation energies corresponding to various dissociation channels that are useful in mass spectrometry experiments. This requires that absolute energies of neutral and singly charged species are evaluated at the same level of theory. As a byproduct of the latter calculations, we have evaluated first and second ionization potentials that are still unavailable in the literature. Harmonic frequencies for the doubly charged species have been also evaluated.

The gas-phase proton affinities of 3-thio-5-oxo, 5-thio-3-oxo, and 3,5-dithio derivatives of 2,7-dimethyl-[1,2,4]-triazepine have been measured by means of Fourier transform ion cyclotron resonance (FTICR) mass spectrometry. The structures and vibrational frequencies of all the stable protonated tautomers and all the transition states connecting them have been obtained by means of the B3LYP density functional method, together with a 6-31G* basis set expansion. The final energies were obtained at the B3LYP/6-311+G(3df,2p) level. In contrast with the results from the analogous thiouracils, our results indicate that all of these compounds behave as sulfur bases in the gas phase. For 5-thio-3-oxo-[1,2,4]-triazepine and 3,5-dithio-[1,2,4]-triazepine, the thiol−enol and the dithiol forms are the most stable protonated species, respectively. Conversely, for 3-thio-5-oxo-[1,2,4]-triazepine, the thiol−ketone form is the most stable one. For 5-thio-3-oxo-[1,2,4]-triazepine and 3,5-dithio-[1,2,4]-triazepine, as it w...

Tandem mass spectrometry was used in the analysis of Cu+-d-glucose complexes. The MIKE spectrum of these complexes generated by FAB shows that the loss of a water molecule is the most important spo...

The [H2, C, N, O]+ potential energy surface (PES) in its triplet state multiplicity has been explored by means of high-level ab initio calculations, carried out in the framework of the G2 theory. F...

High-level ab initio calculations in the framework of the G2 theory have been performed for the [H3, P, F]+ singlet- and triplet-state cations. The bonding characteristics of singlet- and triplet-s...