An Inductively-Coupled Plasma/Selected-Ion Flow Tube (ICP/SIFT) tandem mass spectrometer has been employed in a systematic survey of room-temperature reactions of O 2 with 29 transition-metal ions. The atomic ions are produced at ca. 5500 K in an ICP source and are allowed to decay radiatively and to thermalize by collisions with Ar and He atoms prior to reaction. Rate coefficients were measured for the reactions of first-row atomic ions from Sc + to Zn + , of second-row atomic ions from Y + to Cd + (excluding Tc + ) and of third-row atomic ions from La + to Hg + . Both O-atom abstraction and O 2 addition were observed as primary reaction channels. Periodicities in reactivity are identified and are compared with periodicities in the O-atom affinity of the atomic ion. O-atom abstraction was observed to be efficient when exothermic and inefficient when endothermic. NbO + , MoO + , TaO + , and WO + reacted further in a second O-atom transfer reaction with O 2 . ReO 2 + produced by direct addition of O 2 to Re + reacted further by both O-atom abstraction and O 2 addition. Sequential O 2 addition was observed to produce the higher oxides: MO 3 + (M ) Ti, V, Y, Zr, Hf, Os), MO 4 + (M ) Cr, Fe, Co, Ni, Cu, Nb, Mo, Ru, Rh, Hf, Ta, W, Re, Os, Ir, Pt, Au), MO 5 + (M ) V, Re, Os), MO 6 + (M ) Nb, W, Re) and MO 7 + (M ) V). Novel termolecular reactions second-order in oxygen were identified for Os + and ZrO + at high oxygen concentrations to produce O 2 + and OsO + from Os + and a neutral metal oxide from Zr + .

Dedicated to Edgar Heilbronner on the occasion of his 80th birthday Electron-transfer processes that involve single and doubly charged cations of corannulene (C 20 H 10 ) and coronene (C 24 H 12 ) are examined by three different mass-spectrometric techniques. Photoionization studies give first-ionization energies of IE(C 20 H 10 ) 7.83 AE 0.02 eV and IE(C 24 H 12 ) 7.21 AE 0.02 eV. Photoionizations of the neutrals to the doubly charged cations occur at thresholds of 20.1 AE 0.2 eV and 18.5 AE 0.2 eV for corannulene and coronene, respectively. Energy-resolved charge-stripping mass spectrometry yields kinetic energy deficits of Q min (C 20 H 10 13.8 AE 0.3 eV and Q min (C 24 H 12 12.8 AE 0.3 eV for the transitions from the mono-to the corresponding dications in keV collisions. Reactivity studies of the C 20 H 2 10 and C 24 H 2 12 dications in a selected-ion flow-tube mass spectrometer are used to determine the onsets for the occurrence of single-electron transfer from several neutral reagents to the dications, affording two different monocationic products. With decreasing IEs of the neutral reagents, electron transfer to doubly charged corannulene is first observed with hexafluorobenzene (IE 9.91 eV), while neutrals with lower IEs are required in the case of the coronene dication, e.g., NO 2 (IE 9.75 eV). Density-functional theory is used to support the interpretation of the experimental data. The best estimates of the ionization energies evaluated are IE(C 20 H 10 ) 7.83 AE 0.02 eV and IE(C 24 H 12 ) 7.21 AE 0.02 eV for the neutral molecules, and IE(C 20 H 10 ) 12.3 AE 0.2 eV and IE(C 24 H 12 ) 11.3 AE 0.2 eV for the monocations.Introduction. ± Polycyclic aromatic hydrocarbons (PAHs) are of environmental relevance due to their toxicity combined with their ubiquity as combustion products of organic material in fuel-rich flames [1]. Further, PAHs and their ions are believed to contribute to interstellar absorption bands in the infrared [2a] (for criticism of this hypothesis, however, see [2b]) [3]. For these and other reasons [4], the interest in PAHs has a long tradition [5].As far as first-and second-ionization energies of PAHs are concerned, Tobita et al. provided a comprehensive survey for more than 20 different compounds, ranging from benzene to buckminsterfullerene [6]. However, the data available for the dications are not all unambiguous, and differences may spread over several eV. For example, the appearance energy measurements for the tetracene dication compiled by Tobita et al. range from 18.6 AE 0.2 eV obtained with photoionization to 20.1 AE 0.5 eV determined by charge stripping and 22.1 AE 0.2 eV with electron ionization. Such a magnitude of uncertainties in the evaluation of second-ionization energies appears rather large, thus justifying a re-evaluation that aims at a more accurate determination of this fundamental property for two representative PAHs.Here, we report the results of three different experimental approaches aimed at determining the second ionization energies of corannulene (C 20 H 10 ) a...

Mono- and bis-adducts of benzene of the type M(C6H6)1,2 + have been generated in the gas phase with first-, second-, and third-row transition metal cations, and their reactivities toward molecular oxygen have been measured using an inductively coupled plasma/selected-ion flow tube (ICP/SIFT) tandem mass spectrometer. Trends in reactivity were identified for the metal cation adducts across and down the periodic table. The intrinsic effect of the benzene ligand(s) on the reactivity of the bare metal cations was determined through comparisons with earlier results obtained for the bare metal ions. Molecular oxygen activation by early transition metal cations is preserved in the presence of one benzene ligand but almost disappears in the presence of two benzene molecules. The rate coefficients for O2 addition to late transition metal−benzene adducts are enhanced by up to 4 orders of magnitude in the presence of benzene. Thermochemical information is derived from the occurrence or absence of ligand-switching or metal-abstraction reactions. Oxidation of the benzene ligand itself was observed to be mediated by the transition metal cations V+, Cr+, Fe+, Co+, and Re+ and appeared to result from simultaneous activation of C−H, C−C, and O−O bonds. Catalytic oxidation of the benzene ring observed in the presence of Fe+, Cr+, and Co+ is postulated to result in the production of catechol.

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An inductively coupled plasma (ICP) selected-ion flow tube tandem mass spectrometer has been employed in a systematic survey of room-temperature reactions of C6F6 with 29 transition-metal ions. The atomic ions were produced at ca. 5500 K in an ICP source and were allowed to decay radiatively and to thermalize by collisions with Ar and He atoms prior to reaction, although for some atomic ions, this quenching may be incomplete. Rate coefficients and product distributions were measured for the reactions of first-row atomic ions from Sc+ to Zn+, of second-row atomic ions from Y+ to Cd+ (excluding Tc+), and of third-row atomic ions from La+ to Hg+. Marked differences were observed for reactivities of early and late transition metal cations with regard to both the reaction efficiency and the type of reaction pathway. Remarkable multiple (up to four) fluorine atom abstraction, proceeding close to the collision rate, dominated the chemistry observed with early transition metal cations while simple association of up to two molecules of C6F6 to the metal cation dominated the chemistry of late transition metal cations. Correlations were found between the electronic configuration of the metal cation and the nature of the reaction path and the reaction efficiency. Only the early third-row Hf+, Ta+, and W+ transition-metal ions exhibited some C−C and C−F bond-dissociation channels leading to ring cleavage.