The cationic (C2H4)M+ complexes (M = Cu, Ag, and Au) have been examined by different ab initio molecular orbital, density functional (DFT), and density functional/Hartree−Fock (DFT/HF) hybrid methods using relativistic effective core potentials and a quasi-relativistic approach to account for relativistic effects. For (C2H4)Au+ a substantial relativistic stabilization is observed, such that the computed binding energies are almost twice as high than for (C2H4)Ag+ and still significantly higher than for (C2H4)Cu+. Structural features and energetics obtained at the various computational levels, although they differ significantly in their computational demands, are in satisfying agreement with each other, adding to the level of confidence that can be attributed to the computationally economic DFT and DFT/HF hybrid methods. In order to determine the nature of the bonding in these (C2H4)M+ complexes, an energy decomposition scheme is applied to the DFT results. For all three metal cations, the interaction with ethylene shows large covalent contributions. The major part of the covalent terms stems from σ-donor contribution from the ligand to the metal, whereas π-acceptor bonding (back-bonding) is less important. An atoms-in-molecules (AIM) analysis of the charge density distribution reveals cyclic structures for (C2H4)Au+ and (C2H4)Cu+, whereas (C2H4)Ag+ is T-shaped.

We present a detailed study on dissociative electron attachment (DEA) to isolated gas-phase cytosine (C) and thymine (T). The experimental setup used for these measurements is a crossed electron/neutral beam instrument combined with a quadrupole mass spectrometer. Electron attachment to these biomolecules leads to dissociation into various fragments without a hint of any measurable amount of stable C or T parent anions. The fragment anions with highest abundance are (C-H)and (T-H) -, respectively. Quantum chemical calculations were performed to calculate the electron affinities and binding energies of the different isomers of the (T-H) fragment. Besides (C-H)and (T-H) -, we observed five other fragment anions formed by DEA to cytosine and eight additional product anions were detected in the case of thymine. Ion efficiency curves were measured for all fragment anions in the electron energy range from about 0 to 14 eV. For mixtures of T or C with SF 6 or CCl 4 in the collision chamber, additional resonances close to 0 eV were observed, resulting from ion molecule reactions of SF 6or Clwith the respective biomolecule.

Is host‐guest chemistry possible with fullerenes? Yes, but not as easily as once thought in the euphoric first weeks of preparative fullerene chemistry. Although the occurrence of metal‐ion inclusion is still controversial, indisputable evidence for inclusion of 3He and 4He within C 60˙⊕ and C 70˙⊕ radical ions has now been obtained. A reaction was initiated by collision of C 60˙⊕ and C 60˙⊕ ions with H2, D2, Ar, SF6, and He gases, but only He could be included, which agrees with the results of the initial calculations.

Sections of the potential energy surface of [Fe,C,H4,0]+ ions are probed experimentally by using collisional activation mass spectrometry as well as theoretically by ab initio MO studies. Evidence is presented for the existence of several, clearly distinguishable isomers, some of which are of relevance in the context of methane activation by FeO+ in the gas phase. While this process initially gives rise to the formation of an encounter complex, CH4-FeO+ (1), both spontaneous and post-collisional isomerization occurs to other intermediates formed from 1. The data point to the intermediacy of CH3-Fe-OH+ (3), CH30(H)Fe+ ( 4), and CH2=Fe-OH2+ ( 7); these species account for the formation of FeOH+, Fe+, and FeCH2+, respectively. The isomers CH3-Fe-OH+ (3), CH30(H)Fe+ ( 4), and CH2=Fe-OFi2+ ( 7) can be generated in a clean fashion using appropriate ion/molecule reactions in the gas phase. 4 results by termolecular association of CH3OH and Fe+ as well as decarbonylation of HCOOCH3, 7 is formed in a termolecular reaction from H20 and FeCH2+, and 3 is accessible by S02 loss from the Fe+ complex of CH3S020H. Mixtures of 3 and 7 are obtained by the Fe+-mediated losses of C2H4 from n-C3H7OH and decarbonylation of HCOCH2OH and CH3COOH, pointing to a relatively complex potential energy surface of these systems. No experimental evidence has yet been obtained for the existence of the insertion products H3CO-Fe-H+ ( 8) and H-Fe-CH2OH+ (9) as stable gas-phase species. The former, generated initially by decarbonylation of HCOOCH3, undergoes facile isomerization to H3CO(H)Fe+ (4), and the latter, when generated by decarbonylation of HCOCH2OH, isomerizes to a 1:4 mixture of H3C-Fe-OH+ (3) and H2C=Fe-OH2+ (7). Some of the experimentally probed isomers were further characterized by means of ab initio MO calculations using the MP2/ECP-DZ level of theory, and the computed structural features were found to correlate with the experimental results. The order of stabilities are discussed and compared, where possible, with existing or estimated thermochemical data.

Analysis of radiative association kinetics is a new and promising approach to estimating absolute metal−ligand bond energies for gas-phase metal ions. The method is illustrated using previously published data to estimate the binding energy of aluminum cation to benzene and several deuterium-substituted benzenes. A formulation of radiative association theory is applied which is valid at low association efficiency, and is independent of assumptions about the transition state. Photon emission rates from the complex are derived from McMahon-type analysis of collisional and radiative association data, and alternatively from ab initio calculations of IR radiative intensities, with excellent agreement for all four isotopomers. Analysis of the radiative association data gives a binding energy of 1.53 ± 0.10 eV (35.2 ± 2 kcal mol-1), which is concordant with, but has a smaller estimated uncertainty than, an interpolated thermochemical estimate based on data from other methods. For this system the semiquantitative “standard hydrocarbon” estimate of photon emission rate is a good approximation, but it is shown that in order to give valid predictions of the radiative association rate this scheme requires a correction for the fact that one of the reactants is an atomic ion.