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The formation of water structures can provide significant benefits in organic reactions, stabilizing charge and lowering activation energies. Hydrolysis reactions will frequently rely on water networks to accomplish these goals. Here, we used computational chemistry and experimental kinetics to investigate a model thioester molecule S-ethyl trifluorothioacetate, and extended work on a previously characterized ester p-nitrophenyl trifluoroacetate. We found that the rate-determining steps in these reactions are heavily influenced by the nature of the leaving group. The hydrolysis of S-ethyl trifluorothioacetate was much slower than p-nitrophenyl trifluoroacetate for this reason. We explored differences in the reaction orders with respect to water and examined details of calculated potential energy surfaces of these hydrolysis reactions, highlighting the roles of solvation effects and transition state structures. [ABSTRACT FROM AUTHOR]

The temperature variation of rate constants has been measured for the gas phase reactions of the oxycation O2+ with N atoms and of N2+ with O atoms from 120 to 400 K using a variable temperatureselected ion flow tube. Measured room temperature rate constants, 0.75 × 10-10 cm³ s-1 (±30%) for O2+ with N and 1.4 × 10-10 cm³ s-1 (±30%) for N2+ with O, are in agreement with previously reported values. A temperature dependence of T-0.7(±0.3) is observed for the O2+ + N reaction; however, theN2+ + O reaction is found to be independent of temperature. Calculations at varying levels of theory were used in tandem with experiments to evaluate likely pathways in potential energy surfaces for the reactions of concern. [ABSTRACT FROM AUTHOR]

The exothermicity of the chemi-ionization reaction Sm + O → SmO+ + e- has been re-evaluated through the combination of several experimental methods. The thermal reactivity (300-650 K) of Sm+ and SmO+ with a range of species measured using a selected ion flow tube-mass spectrometer apparatus is reported and provides limits for the bond strength of SmO+, 5.661 eV ≤ D0(Sm+-O) ≤ 6.500 eV. A more precise value is measured to be 5.725 ± 0.07 eV, bracketed by the observed reactivity of Sm+ and SmO+ with several species using a guided ion beam tandem mass spectrometer (GIBMS). Combined with the established Sm ionization energy (IE), this value indicates an exothermicity of the title reaction of 0.08 ± 0.07 eV, ~0.2 eV smaller than previous determinations. In addition, the ionization energy of SmO has been measured by resonantly enhanced two-photon ionization and pulsed-field ionization zero kinetic energy photoelectron spectroscopy to be 5.7427 ± 0.0006 eV, significantly higher than the literature value. Combined with literature bond energies of SmO, this value indicates an exothermicity of the title reaction of 0.14 ± 0.17 eV, independent from and in agreement with the GIBMS result presented here. The evaluated thermochemistry also suggests that D0(SmO) = 5.83 ± 0.07 eV, consistent with but more precise than the literature values. Implications of these results for interpretation of chemical release experiments in the thermosphere are discussed. [ABSTRACT FROM AUTHOR]

Rate constants for the reactions of O2- and O- with N and O atoms have been measured for the first time as a function of temperature from 173 to 500 K for O- reactions and 173 to 400 K for O2- reactions. Room temperature rate constants for O2- reacting with N and O are 3.1 × 10-10 and 1.7 × 10-10 cm3 s-1, respectively, and the corresponding O- rate constants are 1.7 × 10-10 and 1.5 × 10-10 cm3 s-1, in good agreement with previous values. Temperature dependences are about T-1.7 for both O2- reactions and T-0.6 and T-1.3 for the reactions of O- with N and O, respectively. Branching for the O2- reaction with N is found to predominantly form O- (>85%) in contrast to previous measurements, which reported NO2 + e- as the main channel. Calculations point to the present results being correct. The potential energy surface for this reaction was calculated using density functional theory, coupled cluster with singles, doubles (triples), complete active space self-consistent field, and complete active space second-order perturbation methods and is found to be quite complex, with agreement between the calculated surface and the observed kinetic data only possible through the inclusion of dynamical correlation. [ABSTRACT FROM AUTHOR]

A novel technique using a flowing afterglow-Langmuir probe apparatus for measurement of temperature dependences of rate constants for dissociative recombination (DR) is presented. Low (∼1011 cm-3) concentrations of a neutral precursor are added to a noble gas/electron afterglow plasma thermalized at 300-500 K. Charge exchange yields one or many cation species, each of which may undergo DR. Relative ion concentrations are monitored at a fixed reaction time while the initial plasma density is varied between 109 and 1010 cm-3. Modeling of the decrease in concentration of each cation relative to the non-recombining noble gas cation yields the rate constant for DR. The technique is applied to several species (O2+, CO2+, CF3+, N2O+) with previously determined 300 K values, showing excellent agreement. The measurements of those species are extended to 500 K, with good agreement to literature values where they exist. Measurements are also made for a range of CnHm+ (C7H7+, C7H8+, C5H6+, C4H4+, C6H5+, C3H3+, and C6H6+) derived from benzene and toluene neutral precursors. CnHm+ DR rate constants vary from 8-12 × 10-7 cm3 s-1 at 300 K with temperature dependences of approximately T-0.7. Where prior measurements exist these results are in agreement, with the exception of C3H3+ where the present results disagree with a previously reported flat temperature dependence. [ABSTRACT FROM AUTHOR]

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, BiSn4- is a stable cluster and fits aromatic criteria, while BiSn5- 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. [ABSTRACT FROM AUTHOR]

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 reaction. [ABSTRACT FROM AUTHOR]

The reactions of FeO+ with H2 and of Fe+ with N2O were studied with respect to the production and reactivity of electronically excited 4Fe+ cations. The reaction of electronic ground state 6FeO+ with H2 was found to predominantly produce electronically excited 4Fe+ as opposed to electronic ground state 6Fe+ corresponding to a spin-allowed reaction. 4Fe+ was observed to react with N2O with a rate constant of 2.3 (+0.3/−0.8) × 10−11 cm3 molecule−1 s−1, smaller than the ground state 6Fe+ rate constant of 3.2 (±0.5) × 10−11 cm3 molecule−1 s−1 (at room temperature). While the overall reaction of 6FeO+ 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 4Fe+ 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 4Fe+, subsequently reacting with N2O. The measured rate constant has allowed for a more detailed understanding of the ground state 6Fe+ 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 4Fe+ by He was found to be slow, with a rate constant ＜3 × 10−14 cm3 molecule−1 s−1. [ABSTRACT FROM AUTHOR]