Coupling an electrospray source and a solids probe/chemical ionization source to a selected ion flow tube apparatus

Melko, Joshua J.; Ard, Shaun G.; Shuman, Nicholas S.; Pedder, Randall E.; Taormina, Christopher R.; Viggiano, Albert A.

doi:10.1063/1.4927716

Cited by 8 publications

(6 citation statements)

References 25 publications

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“…Recently, Viggiano and co-workers reported a new ESI source, designed by Ardara Corp., for their SIFT . Our ESI design utilizes an ion funnel and is similar to that developed for guided-ion beam experiments. , A schematic of our ESI source is shown in Figure .…”

Section: Methodsmentioning

confidence: 99%

Experimental and Theoretical Studies of the Reactivity and Thermochemistry of Dicyanamide: N(CN)₂^–

et al. 2016

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Dicyanamide [N(CN)2(-)] is a common anionic component of ionic liquids, several of which have shown hypergolic reactivity upon mixing with white-fuming nitric acid. In this study, we explore the thermochemistry of dicyanamide and its reactivity with nitric acid and other molecules to gain insight into the initial stages of the hypergolic phenomenon. We have developed and utilized an electrospray ion source for our selected ion flow tube (SIFT) to generate the dicyanamide anion. We have explored the general reactivity of this ion with several neutral molecules and atoms. Dicyanamide does not show reactivity with O2, H2SO4, H2O2, DBr, HCl, NH3, N2O, SO2, COS, CO2, CH3OH, H2O, CH4, N2, CF4, or SF6 (k < 1 × 10(-12) cm(3)/s); moreover, dicyanamide does not react with N atom, O atom, or electronically excited molecular oxygen (k < 5 × 10(-12) cm(3)/s), and our previous studies showed no reactivity with H atom. However, at 0.45 Torr helium, we observe the adduct of dicyanamide with nitric acid with an effective bimolecular rate constant of 2.7 × 10(-10) cm(3)/s. Intrinsically, dicyanamide is a very stable anion in the gas phase, as illustrated by its lack of reactivity, high electron-binding energy, and low proton affinity. The lack of reactivity of dicyanamide with H2SO4 gives an upper limit for the gas-phase deprotonation enthalpy of the parent compound (HNCNCN; <310 ± 3 kcal/mol). This limit is in agreement with theoretical calculations at the MP2/6-311++G(d,p) level of theory, finding that ΔH298 K(HNCNCN) = 308.5 kcal/mol. Dicyanamide has two different proton acceptor sites. Experimental and computational results indicate that it is lower in energy to protonate the terminal nitrile nitrogen than the central nitrogen. Although proton transfer to dicyanamide was not observed for any of the acidic molecules investigated here, the calculations on dicyanamide with one to three nitric acid molecules reveal that higher-order solvation can favor exothermic proton transfer. Furthermore, the formation of 1,5-dinitrobiuret, proposed to be the key intermediate during the hypergolic ignition of dicyanamide ionic liquids with nitric acid, is investigated by calculation of the reaction coordinate. Our results suggest that solvation dynamics of dicyanamide with nitric acid play an important role in hypergolic ignition and the interactions at the droplet/condensed-phase surface between the two hypergolic liquids are very important. Moreover, dicyanamide exists in the atmosphere of Saturn's moon, Titan; the intrinsic stability of dicyanamide strongly suggests that it may exist in molecular clouds of the interstellar medium, especially in regions where other stable carbon-nitrogen anions have been detected.

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Section: Methodsmentioning

confidence: 99%

Experimental and Theoretical Studies of the Reactivity and Thermochemistry of Dicyanamide: N(CN)₂^–

et al. 2016

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“…The upstream end of the instrument 21 has gone through an even bigger upgrade. In order to make it easier to change sources, a quadrupole bender (F) allows three ions sources to be attached simultaneously.…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

Old School Techniques with Modern Capabilities: Kinetics Determination of Dynamical Information Such as Barriers, Multiple Entrance Channel Complexes, Product States, Spin Crossings, and Size Effects in Metallic Ion–Molecule Reactions

2021

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We show how the powerful combination of temperature-dependent kinetics coupled with detailed statistical modeling can be used to derive dynamical information about transition state barrier heights, the importance of multiple entrance channel complexes, crossings between spin surfaces, energetics, product states, and other information for metal-ion reactions. The methods are not new, but with improved computers, ion sources, ion transport, and better detection techniques, the ability to derive such parameters from the combination of methods has improved greatly. Temperature-dependent kinetics is very sensitive to the above list of parameters because the energy is varied in a controlled way that can be easily modeled. The present measurements, performed in our variable-ion source temperature-adjustable selected-ion flow tube (VISTA-SIFT), have been enabled by advances in ion transport and injection improvements so that dim sources can be used. Replacing the quadrupole mass spectrometer detector with a time-of-flight mass spectrometer solved additional problems. Quantum chemical calculations have improved greatly and provide details about the surfaces, as well as frequencies, to use as starting points for the statistical modeling. For ion–molecule reactions, incorporation of both energy and angular momentum effects are important and we have developed an in-house computer program, based on the work of Juergen Troe, to rapidly compare statistical modeling predictions to the experimental data. As we show, modeling the kinetics data can often determine the most important parameters controlling the reactivity and deriving them is much simpler and usually more accurate than detailed ab initio calculations or dynamical modeling. Additionally, we show that even without statistical modeling, temperature-dependent rate constants as a function of metal anion cluster size can be used to show that such species react by the same mechanism as surfaces. In this review, we discuss reactions of metallic atomic ions, small metal oxide ions, mixed metal oxide ions, and a series of metallic anionic cluster reactions with small molecules such as CO, O2, CO2, N2O, CH4, and several other species. Particular attention was paid to reactions involving bond activation pertinent to catalysis.

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“…Thermal kinetic measurements were performed on a variable temperature selected ion flow tube (VT-SIFT) at the Air Force Research Laboratory, described in detail previously. , Sm + was formed using a glow discharge rod source, similar to that described above, and detailed elsewhere . Briefly, approximately 1 std L min –1 of a 10:1 He to Ar gas mix at a pressure of approximately 1 Torr flowed over an iron “boat” containing Sm chips.…”

Section: Experimental and Theoretical Methodsmentioning

confidence: 99%

Lanthanides as Catalysts: Guided Ion Beam and Theoretical Studies of Sm⁺ + COS

et al. 2018

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Reactions of samarium cations with carbonyl sulfide are examined using a guided ion beam tandem mass spectrometer and a variable temperature selected ion flow tube apparatus. Formation of SmS + CO is observed in both instruments with a kinetic energy and temperature dependence demonstrating a barrierless reaction occurring with an efficiency of 26 ± 9%. Formation of SmO + CS is also observed at high kinetic energies and exhibits a threshold determined as 2.81 ± 0.32 eV, substantially higher than expected from known thermochemistry. The potential energy surfaces for these reactions along sextet and octet spin surfaces are also examined theoretically at the MP2 and CCSD(T) levels. The observed barrier for oxidation is shown to likely correspond to the energy of the crossing between surfaces corresponding to the ground state electronic configuration of Sm (F,4f6s) and an excited surface having two electrons in the valence space (excluding 4f), which are needed to form the strong SmO bond. In contrast, the S-CO bond is activated much more readily because this crossing occurs at much lower energies. This result is attributed to the much weaker S-CO bond energy as well as the ability of sulfur to bind effectively at different angles. Although both reactions are spin-forbidden, evidence for a more efficient spin-allowed process is also observed in the SmS + CO cross section.

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Coupling an electrospray source and a solids probe/chemical ionization source to a selected ion flow tube apparatus

Cited by 8 publications

References 25 publications

Experimental and Theoretical Studies of the Reactivity and Thermochemistry of Dicyanamide: N(CN)₂^–

Experimental and Theoretical Studies of the Reactivity and Thermochemistry of Dicyanamide: N(CN)₂^–

Old School Techniques with Modern Capabilities: Kinetics Determination of Dynamical Information Such as Barriers, Multiple Entrance Channel Complexes, Product States, Spin Crossings, and Size Effects in Metallic Ion–Molecule Reactions

Lanthanides as Catalysts: Guided Ion Beam and Theoretical Studies of Sm⁺ + COS

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Coupling an electrospray source and a solids probe/chemical ionization source to a selected ion flow tube apparatus

Cited by 8 publications

References 25 publications

Experimental and Theoretical Studies of the Reactivity and Thermochemistry of Dicyanamide: N(CN)2–

Experimental and Theoretical Studies of the Reactivity and Thermochemistry of Dicyanamide: N(CN)2–

Old School Techniques with Modern Capabilities: Kinetics Determination of Dynamical Information Such as Barriers, Multiple Entrance Channel Complexes, Product States, Spin Crossings, and Size Effects in Metallic Ion–Molecule Reactions

Lanthanides as Catalysts: Guided Ion Beam and Theoretical Studies of Sm+ + COS

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Experimental and Theoretical Studies of the Reactivity and Thermochemistry of Dicyanamide: N(CN)₂^–

Experimental and Theoretical Studies of the Reactivity and Thermochemistry of Dicyanamide: N(CN)₂^–

Lanthanides as Catalysts: Guided Ion Beam and Theoretical Studies of Sm⁺ + COS