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We present rate constants and product branching ratios for the reactions of FeOx+ (x = 0–4) with ozone at 500 K. Fe+ is observed to react with ozone at the collision rate to produce FeO+ + O2. The FeO+ in turn reacts with ozone at the collision rate to yield both Fe+ and FeO2+ product channels. Ions up to FeO4+ display similar reactivity patterns. Three-body clustering reactions with O2 prevent us from measuring accurate rate constants at 300 K although the data do suggest that the efficiency is also high. Therefore, it is probable that little to no temperature dependence exists over this range. Implications of our measurements to the regulation of atmospheric iron and ozone are discussed. Density functional calculations on the reaction of Fe+ with ozone show no substantial kinetic barriers to make the FeO+ + O2 product channel, which is consistent with the reaction’s efficiency. While a pathway to make FeO2+ + O is also found to be barrierless, our experiments indicate no primary FeO2+ formation for this...

The temperature dependent kinetics of Ni+ + O3 and of NiO+ + CH4/CD4 are measured from 300 to 600 K using a selected-ion flow tube apparatus. Together, these reactions comprise a catalytic cycle converting CH4 to CH3OH. The reaction of Ni+ + O3 proceeds at the collisional limit, faster than previously reported at 300 K. The NiO+ product reacts further with O3, also at the collisional limit, yielding both higher oxides (up to NiO5+ is observed) as well as undergoing an apparent reduction back to Ni+. This apparent reduction channel is due to the oxidation channel yielding NiO2+* with sufficient energy to dissociate. 4NiO+ + CH4 (CD4) (whereas 4NiO+ refers to the quartet state of NiO+) proceeds with a rate constant of (2.6 ± 0.4) × 10–10 cm3 s–1 [(1.8 ± 0.5) × 10–10 cm3 s–1] at 300 K and a temperature dependence of ∼T–0.7±0.3 (∼T–1.1±0.4), producing only the 2Ni+ + 1CH3OH channel up to 600 K. Statistical modeling of the reaction based on calculated stationary points along the reaction coordinate reproduces ...

The reactivity of microsolvated fluoride ions, F−(CH3OH)0–2, with methyl, ethyl, n-propyl, and t-butyl bromide is evaluated over a broad range of temperatures. Significant decreases in reactivity are observed as either solvation or temperature increases. Increasing solvation increases sensitivity to the reaction barrier as revealed by a larger temperature dependence. These reactions are dominated by an SN2 mechanism for the methyl bromide reaction, while the SN2 and E2 mechanisms compete for the reactions with ethyl and n-propyl bromide reactions. The elimination mechanism, with some association, dominates the t-butyl bromide reactions. In all cases the unsolvated bromide ion is the primary ionic product. Branching ratios are discussed in both qualitative and quantitative terms for all reactions at 300 K.

A new ion detection scheme incorporating both time-of-flight and quadrupole instrumentation has been implemented on a variable temperature selected ion flow tube and is described here. The new detection region retains typical quadrupole detection for the study of most systems, and adds time-of-flight capability to study systems over a wide mass range while minimizing the effects of mass discrimination. Experiments verify the accuracy of the kinetics obtained with time-of-flight detection. We find excellent agreement with previously published rate constants and product branching for the reactions of Ar+ with SF6 and C2H4. Additionally, new results are presented for the reaction of Ar+ with WF6, observing a rate constant of 1.23 × 10−9 cm3 s−1, with product branching of 0.9 and 0.1 to WF5+ and WF6+ respectively.

The rates of the reactions Fe(+) + N2O → FeO(+) + N2 and FeO(+) + CO → Fe(+) + CO2 are modeled by statistical rate theory accounting for energy- and angular momentum-specific rate constants for formation of the primary and secondary cationic adducts and their backward and forward reactions. The reactions are both suggested to proceed on sextet and quartet potential energy surfaces with efficient, but probably not complete, equilibration by spin-inversion of the populations of the sextet and quartet adducts. The influence of spin-inversion on the overall reaction rate is investigated. The differences of the two reaction rates mostly are due to different numbers of entrance states (atom + linear rotor or linear rotor + linear rotor, respectively). The reaction Fe(+) + N2O was studied either with (6)Fe(+) or with (4)Fe(+) reactants. Differences in the rate constants of (6)Fe(+) and (4)Fe(+) reacting with N2O are attributed to different contributions from electronically excited potential energy surfaces, such as they originate from the open-electronic shell reactants.

Direct dynamics simulations and selected ion flow tube (SIFT) experiments were performed to study the kinetics and dynamics of the OH(-) + CH3I reaction versus temperature. This work complements previous direct dynamics simulation and molecular beam ion imaging experiments of this reaction versus reaction collision energy (Xie et al. J. Phys. Chem. A 2013, 117, 7162). The simulations and experiments are in quite good agreement. Both identify the SN2, OH(-) + CH3I → CH3OH + I(-), and proton transfer, OH(-) + CH3I → CH2I(-) + H2O, reactions as having nearly equal importance. In the experiments, the SN2 pathway constitutes 0.64 ± 0.05, 0.56 ± 0.05, 0.51 ± 0.05, and 0.46 ± 0.05 of the total reaction at 210, 300, 400, and 500 K, respectively. For the simulations this fraction is 0.56 ± 0.06, 0.55 ± 0.04, and 0.50 ± 0.05 at 300, 400, and 500 K, respectively. The experimental total reaction rate constant is (2.3 ± 0.6) × 10(-9), (1.7 ± 0.4) × 10(-9), (1.9 ± 0.5) × 10(-9), and (1.8 ± 0.5) × 10(-9) cm(3) s(-1) at 210, 300, 400, and 500 K, respectively, which is approximately 25% smaller than the collision capture value. The simulation values for this rate constant are (1.7 ± 0.2) × 10(-9), (1.8 ± 0.1) × 10(-9), and (1.6 ± 0.1) × 10(-9) cm(3)s(-1) at 300, 400, and 500 K. From the simulations, direct rebound and stripping mechanisms as well as multiple indirect mechanisms are identified as the atomic-level reaction mechanisms for both the SN2 and proton-transfer pathways. For the SN2 reaction the direct and indirect mechanisms have nearly equal probabilities; the direct mechanisms are slightly more probable, and direct rebound is more important than direct stripping. For the proton-transfer pathway the indirect mechanisms are more important than the direct mechanisms, and stripping is significantly more important than rebound for the latter. Calculations were performed with the OH(-) quantum number J equal to 0, 3, and 6 to investigate the effect of OH(-) rotational excitation on the OH(-) + CH3I reaction dynamics. The overall reaction probability and the probabilities for the SN2 and proton-transfer pathways have little dependence on J. Possible effects on the atomistic mechanisms were investigated for the SN2 pathway and the probability of the direct rebound mechanism increased with J. However, the other atomistic mechanisms were not appreciably affected by J.

We have studied the reactions of Ar+, O-2(+), and C2H2* with toluene (CH3-C6H5) and ethylbenzene (C2H5-C6H5) as a function of temperature. Ar+ reacts with C7H8 at the collision rate constant at both 300 and 500 K to produce mainly C7H7+ cations (similar to 85%), with the remainder of the reactivity divided into numerous small channels. The fraction of C7H7+ produced as benzylium(+) (6 membered ring, Bz(+)) as opposed to tropylium(+) (7 membered ring, Tr+) is determined through ion-molecule reactivity to be primarily Bz(+). The reaction of Ar+ with C8H10 proceeds at slightly lower than the collision rate constant at 300 K, but increases to the collision rate constant at 500 K. Over 80% of the products were C7H7+, the large majority of which also is Bz(+). The O-2(+) reaction with C8H10 proceeds at the collision rate constant and produces C8H10+, C6H6+, and C7H7+, with the latter again primarily being Bz(+). C7H7+ was found to react with both CH3-C6H5 and C2H5-C6H5 by both collisionally stabilized clustering and a bimolecular reaction forming R-C6H4-CH2+. At 300 K the rate constants are about half of the collision rate constant and drop rapidly with temperature. About 2/3 of the products are clusters at 300 K, 1/3 at 400 K, and negligible amounts at 500 and 600 K. Evidence for thermal dissociation of the cluster is presented. Calculations show the most stable structure is the one where the methylene group of benzylium is coordinated at the para position of the alkylbenzene, with one phenyl group approximately 45 degrees out of plane relative to the other. A bond strength of 15-16 kcal mol(-1) is calculated for both neutrals. Numerous less stable structures were found.

The electronic and structural properties of small monomagnesium oxide clusters, MgO(x)(-) and MgO(x) (x = 1-4), have been investigated using a synergistic approach combining photoelectron imaging spectroscopy and first principles electronic structure calculations. The adiabatic detachment energy (ADE) and vertical detachment energy (VDE) of MgO(x)(-) clusters along with the photoelectron angular distributions (PADs) are determined experimentally. The measured PADs of the clusters are dependent on both the orbital symmetry and electron kinetic energies. Density-functional theory (DFT) calculations were performed to explore the optimized geometries of neutral and anionic MgO(x) clusters. The theoretical ADE and VDE values calculated according to the optimized geometries are in good agreement with our experimental measurements. In addition, MgO(-) and MgO4 clusters are found to have enhanced relative stability in the corresponding anionic and neutral series, based on both theoretical parameters and the experimental cluster distribution.

We report for the first time temperature dependences (from 300 to 600 K) of the reactions of Fe(+) and FeO(+) with NO and NO(2). Both ions react quickly with NO(2), and their rate constants have weak negative temperature dependences. The former is consistent with the calculated energy profile along the Fe(+) + NO(2) reaction coordinate. Ground state Fe(+) reacts with NO(2) to produce only FeO(+), while FeO(+) reacts with NO(2) to produce NO(+) exclusively. Certain source conditions produce excited Fe(+), as evidenced by production of primary NO(+), which is endothermic with the ground state by 0.35 eV. The room temperature rate constants are in agreement with previous values. For the reactions of Fe(+) and FeO(+) with NO, we find an upper limit of

The electronic structure of Al(n)X (n = 1-6; X = As, Sb) clusters has been investigated using a synergistic approach combining negative ion photoelectron spectroscopy and first principles electronic structure calculations. It is shown that Al(3)X and Al(5)X exhibit enhanced energetic stability, as evidenced from calculated removal and embedding energies as well as chemical stability manifested through a large gap between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO). However, the stabilities of these species are derived from different mechanisms. Al(3)As and Al(3)Sb, with HOMO-LUMO gaps of 1.86 and 1.73 eV, respectively, are shown to have planar geometries where the p orbitals combine to form one pi and two sigma aromatic orbitals reminiscent of conventional all-metal aromatic species. Al(5)As and Al(5)Sb, with 20 valence electrons, possess a closed electronic shell (1s(2), 1p(6), 1d(10), 2s(2)) within a jellium framework and have HOMO-LUMO gaps of 1.12 and 1.17 eV, respectively.

An experimental and theoretical study of bismuth-doped aluminum clusters in the gas phase has revealed two particularly stable clusters, namely, Al(3)Bi and Al(5)Bi. We show that their electronic structure can be understood in terms of the aromatic and "Jellium" models, respectively. Negative ion photodetachment spectra provide a fingerprint of the electronic states in Al(n)Bi(-) (n = 1-5) anions, while theoretical investigations reveal the nature of the electronic orbitals involved. Together, the findings reveal that the all-metal Al(3)Bi cluster with 14 valence electrons is a cyclic, planar structure with a calculated large ionization potential of 7.08 eV, a low electron affinity of 1.41 eV, and a large gap of 1.69 eV between the highest occupied and lowest unoccupied molecular orbitals (HOMO-LUMO gap). The Al(3)Bi cluster has molecular orbitals reminiscent of aromatic systems and is a neutral cluster with no need for counterion or ligand support. A slightly larger cluster, Al(5)Bi, has 20 valence electrons and is another highly stable compact structure with a calculated large ionization potential of 6.51 eV and a large HOMO-LUMO gap of 1.15 eV. This cluster's stability is rooted in a Jellium electronic shell closing. The formation of stable species using aromatic bonding allows us to extend the idea of cluster-assembled materials built out of stable clusters with Jellium shell closings (superatoms) to include ones involving aromatic building blocks.

The reactions of FeO(+) with H2 and of Fe(+) with N2O were studied with respect to the production and reactivity of electronically excited (4)Fe(+) cations. The reaction of electronic ground state (6)FeO(+) with H2 was found to predominantly produce electronically excited (4)Fe(+) as opposed to electronic ground state (6)Fe(+) corresponding to a spin-allowed reaction. (4)Fe(+) was observed to react with N2O with a rate constant of 2.3 (+0.3/-0.8) × 10(-11) cm(3) molecule(-1) s(-1), smaller than the ground state (6)Fe(+) rate constant of 3.2 (±0.5) × 10(-11) cm(3) molecule(-1) s(-1) (at room temperature). While the overall reaction of (6)FeO(+) with H2 within the Two-State-Reactivity concept is governed by efficient sextet-quartet spin-inversion in the initial reaction complex, the observation of predominant (4)Fe(+) production in the reaction is attributed to a much less efficient quartet-sextet back-inversion in the final reaction complex. Average spin-inversion probabilities are estimated by statistical modeling of spin-inversion processes and related to the properties of spin-orbit coupling along the reaction coordinate. The reaction of FeO(+) with H2 served as a source for (4)Fe(+), subsequently reacting with N2O. The measured rate constant has allowed for a more detailed understanding of the ground state (6)Fe(+) reaction with N2O, leading to a significantly improved statistical modeling of the previously measured temperature dependence of the reaction. In particular, evidence for the participation of electronically excited states of the reaction complex was found. Deexcitation of (4)Fe(+) by He was found to be slow, with a rate constant3 × 10(-14) cm(3) molecule(-1) s(-1).

We have determined the rate constants and branching ratios for the reactions of CO(+) with CH4 and CD4 in a variable-temperature selected ion flow tube. We find that the rate constants are collisional for all temperatures measured (193-700 K for CH4 and 193-500 K for CD4). For the CH4 reaction, three product channels are identified, which include charge transfer (CH4(+) + CO), H-atom transfer (HCO(+) + CH3), and H-atom expulsion (CH3CO(+) + H). H-atom transfer is slightly preferred to charge transfer at low temperature, with the charge-transfer product increasing in contribution as the temperature is increased (H-atom expulsion is a minor product for all temperatures). Analogous products are identified for the CD4 reaction. Density functional calculations on the CO(+) + CH4 reaction were also conducted, revealing that the relative temperature dependences of the charge-transfer and H-atom transfer pathways are consistent with an initial charge transfer followed by proton transfer.

The temperature dependences of the rate constants and product branching ratios for the reactions of FeO(+) with CH4 and CD4 have been measured from 123 to 700 K. The 300 K rate constants are 9.5 × 10(-11) and 5.1 × 10(-11) cm(3) s(-1) for the CH4 and CD4 reactions, respectively. At low temperatures, the Fe(+) + CH3OH/CD3OD product channel dominates, while at higher temperatures, FeOH(+)/FeOD(+) + CH3/CD3 becomes the majority channel. The data were found to connect well with previous experiments at higher translational energies. The kinetics were simulated using a statistical adiabatic channel model (vibrations are adiabatic during approach of the reactants), which reproduced the experimental data of both reactions well over the extended temperature and energy ranges. Stationary point energies along the reaction pathway determined by ab initio calculations seemed to be only approximate and were allowed to vary in the statistical model. The model shows a crossing from the ground-state sextet surface to the excited quartet surface with large efficiency, indicating that both states are involved. The reaction bottleneck for the reaction is found to be the quartet barrier, for CH4 modeled as -22 kJ mol(-1) relative to the sextet reactants. Contrary to previous rationalizations, neither less favorable spin-crossing at increased energies nor the opening of additional reaction channels is needed to explain the temperature dependence of the product branching fractions. It is found that a proper treatment of state-specific rotations is crucial. The modeled energy for the FeOH(+) + CH3 channel (-1 kJ mol(-1)) agrees with the experimental thermochemical value, while the modeled energy of the Fe(+) + CH3OH channel (-10 kJ mol(-1)) corresponds to the quartet iron product, provided that spin-switching near the products is inefficient. Alternative possibilities for spin switching during the reaction are considered. The modeling provides unique insight into the reaction mechanisms as well as energetic benchmarks for the reaction surface.

Rate coefficients and branching fractions have been measured for electron attachment to perfluoromethylcyclohexane, C(7)F(14), along with thermal detachment rate coefficients for C(7)F(14)(-), from 300 to 630 K, using a flowing-afterglow Langmuir-probe apparatus. The attachment rate coefficient at room temperature is 4.5 ± 1.2 × 10(-8) cm(3) s(-1) and increases with temperature at a rate described by an activation energy of 50 ± 25 meV. Thermal electron detachment is negligible at room temperature, but measurable at 600 K and above, reaching 2300 ± 1300 s(-1) at 630 K. Analysis of the attachment-detachment equilibrium yields EA(C(7)F(14)) = 1.02 ± 0.06 eV, in agreement with the literature value while more than halving the uncertainty. Implications of the measurement for the electron affinity of SF(6) are discussed. The dominant product of electron attachment is the parent anion, but C(6)F(11)(-) and C(7)F(13)(-) are also observed at very low levels (

The geometric and electronic structure of Pb(x)Sb(y)(-) and Sn(x)Bi(y)(-) clusters are investigated by photoelectron spectroscopy and theoretical methods. It is found that PbSb(2)(-) and SnBi(2)(-) have similar spectroscopic patterns, reflecting correlations in electronic nature that are a result of their isoelectronic character and common geometries. Analogous findings are presented for Pb(2)Sb(2)(-) and Sn(2)Bi(2)(-). Further, we investigate the effect of altering the total valence count, and separately the geometry, on spectroscopic patterns. We conclude that these heavy p-block elements are interchangeable and that the electronic structure correspondence can be preserved regardless of elemental composition. This represents an extension of the traditional concepts of periodicity, where elements of similar valence configuration are grouped into columns. Instead, elements from different columns may be combined to yield similarities in chemistry, given the overall valence count is preserved.

Three-dimensional aromaticity is shown to play a role in the stability of deltahedral Zintl clusters and here we examine the connection between aromaticity and stability. In order to gain further insight, we have studied Zintl analogs comprised of bismuth doped tin clusters with photoelectron spectroscopy and theoretical methods. To assign aromaticity, we examine the ring currents induced around the cage by using the nucleus independent chemical shift. In the current study, BiSn(4)(-) is a stable cluster and fits aromatic criteria, while BiSn(5)(-) is found to fit antiaromatic criteria and has reduced stability. The more stable clusters exhibit an aromatic character which originates from weakly interacting s-states and bonding orbitals parallel to the surface of the cluster, while nonbonding lone pairs perpendicular to the surface of the cluster account for antiaromaticity and reduced stability. The effect of three-dimensional aromaticity on the electronic structure does not result in degeneracies, so the resulting variations in stability are smaller than those seen in conventional aromaticity.

The ion-molecule reactions F-e+ + N2O -> FeO+ + N-2 and FeO+ + CO -> Fe+ + CO2, which catalyze the reaction CO + N2O -> CO2 + N-2, have been studied over the temperature range 120-700 K using a variable temperature selected ion flow tube apparatus. Values of the rate constants for the former two reactions were experimentally derived as k(2) (10(-11) cm(3) s(-1)) = 2.0(+/- 0.3) (T/300)(-1.5(+/- 0.2)) + 6.3(+/- 0.9) exp(-515(+/- 77)/T) and k(3) (10(-10) cm(3) s(-1)) = 3.1(+/- 0.1) (T/300)(-0.9(+/- 0.1)). Characterizing the energy parameters of the reactions by density functional theory at the B3LYP/TZVP level, the rate constants are modeled, accounting for the intermediate formation of complexes. The reactions are characterized by nonstatistical intrinsic dynamics and rotation-dependent competition between forward and backward fluxes. For Fe+ + N2O, sextet-quartet switching of the potential energy surfaces is quantified. The rate constant for the clustering reaction FeO+ + N2O + He -> FeO(N2O)(+) + He was also measured, being k(4) (10(-27) cm(6) s(-1)) = 1.1(+/- 0.1) (T/300)(-2.5(+/- 0.1)) in the low pressure limit, and analyzed in terms of unimolecular rate theory.