Time-resolved quantification of key species and mechanistic insights in low-temperature tetrahydrofuran oxidation.

We investigate the kinetics and report the time-resolved concentrations of key chemical species in the oxidation of tetrahydrofuran (THF) at 7500 torr and 450-675 K. Experiments are carried out using high-pressure multiplexed photoionization mass spectrometry (MPIMS) combined with tunable vacuum ultraviolet radiation from the Berkely Lab Advanced Light Source. Intermediates and products are quantified using reference photoionization (PI) cross sections, when available, and constrained by a global carbon balance tracking approach at all experimental temperatures simultaneously for the species without reference cross sections.

Glycine in a basket: protonated complexes of 1,1,,-tetramethyl[](2,11)teropyrenophane ( = 7, 8, 9) with glycine in the gas-phase.

Protonated complexes composed of a basket-like host molecule 1,1,,-tetramethyl[](2,11)teropyrenophanes (TMnTP) ( = 7, 8, 9) and glycine as a guest were studied in the gas phase by experimental and computational methods. Blackbody infrared radiative dissociation (BIRD) experiments of [(TMnTP)(Gly)]H not only provided the observed Arrhenius parameters (activation energies, obsa, and frequency factors, A) but also suggested the existence of two populations of isomeric complexes of [(TMnTP)(Gly)]H, termed fast dissociating (FD) and slow dissociating (SD), due to their relative BIRD rate constants. Master equation modeling was conducted to obtain the threshold dissociation energies of the host-guest complexes.

Infrared multiple photon dissociation action spectroscopy of protonated unsymmetrical dimethylhydrazine and proton-bound dimers of hydrazine and unsymmetrical dimethylhydrazine.

The gas-phase structures of protonated unsymmetrical 1,1-dimethylhydrazine (UDMH) and the proton-bound dimers of UDMH and hydrazine are examined by infrared multiple photon dissociation (IRMPD) action spectroscopy utilizing light generated by a free electron laser and an optical parametric oscillator laser system. To identify the structures present in the experimental studies, the measured IRMPD spectra are compared to spectra calculated at the B3LYP-GD3BJ/6-311+G(d,p) level of theory. These comparisons show that protonated UDMH binds the proton at the methylated nitrogen atom (α) with two low-lying α conformers probably being populated.

Reactions of U with H, D, and HD Studied by Guided Ion Beam Tandem Mass Spectrometry and Theory.

The kinetic energy-dependent reactions of the atomic actinide uranium cation (U) with H, D, and HD were examined by guided ion beam tandem mass spectrometry. An average 0 K bond dissociation energy of (U - H) = 2.48 ± 0.

Quantitative Detection of Products and Radical Intermediates in Low-Temperature Oxidation of Cyclopentane.

We present a combined experimental and theoretical investigation of the autoignition chemistry of a prototypical cyclic hydrocarbon, cyclopentane. Experiments using a high-pressure photolysis reactor coupled to time-resolved synchrotron VUV photoionization mass spectrometry directly probe the short-lived radical intermediates and products in cyclopentane oxidation reactions. We detect key peroxy radical intermediates ROO and OOQOOH, as well as several hydroperoxides, formed by second O addition.

Relative Energetics of the Gas Phase Protomers of -Aminobenzoic Acid and the Effect of Protonation Site on Fragmentation.

Guided ion beam tandem mass spectrometry (GIBMS) is used to investigate the energy-dependent threshold collision-induced dissociation (TCID) of the two protonated isomers (protomers) of -aminobenzoic acid (p-ABA). The O-protomer of p-ABA (protonated at the carbonyl oxygen) was generated via electrospray ionization (ESI) from a methanol/water solution, whereas the N-protomer (protonated at the amine) was produced via ESI from an acetonitrile/water solution. The two protomers are clearly distinguishable from differences in the onsets of the fragmentation channels and in the abundance and identity of the products observed.

Direct time-resolved detection and quantification of key reactive intermediates in diethyl ether oxidation at T = 450-600 K.

High-pressure multiplexed photoionization mass spectrometry (MPIMS) with tunable vacuum ultraviolet (VUV) ionization radiation from the Lawrence Berkeley Labs Advanced Light Source is used to investigate the oxidation of diethyl ether (DEE). Kinetics and photoionization (PI) spectra are simultaneously measured for the species formed. Several stable products from DEE oxidation are identified and quantified using reference PI cross-sections.

Benzhydrylpyridinium Ions: A New Class of Thermometer Ions for the Characterization of Electrospray-Ionization Mass Spectrometers.

Previous attempts to characterize the internal energies of ions produced by electrospray ionization (ESI) have chiefly relied upon benzylpyridinium ions, R-BnPy, as thermometer ions. However, these systems are not well suited for this purpose because of their relatively high dissociation energies. Here, we propose benzhydrylpyridinium ions, R,R'-BhPy, as a new class of thermometer ions.

Samarium cation (Sm) reactions with H, D, and HD: SmH bond energy and mechanistic insights from guided ion beam and theoretical studies.

Guided ion beam tandem mass spectrometry is used to study the reaction of the lanthanide samarium cation (Sm) with H and its isotopologues (HD and D) as a function of collision energy. Modeling the resulting energy dependent product ion cross sections from these endothermic reactions yields 2.03 ± 0.

Activation of H by Gadolinium Cation (Gd): Bond Energy of GdH and Mechanistic Insights from Guided Ion Beam and Theoretical Studies.

The energy-dependent reactions of the lanthanide gadolinium cation (Gd) with H, D, and HD are investigated using guided ion beam tandem mass spectrometry. From analysis of the resulting endothermic product ion cross sections, the 0 K bond dissociation energy for GdH is measured to be 2.18 ± 0.

Guided ion beam and theoretical studies of the bond energy of SmS.

Previous work has shown that atomic samarium cations react with carbonyl sulfide to form SmS + CO in an exothermic and barrierless process. To characterize this reaction further, the bond energy of SmS is determined in the present study using guided ion beam tandem mass spectrometry. Reactions of SmS with Xe, CO, and O are examined.

Gadolinium cation (Gd) reaction with O: Potential energy surface mapped experimentally and with theory.

Guided ion beam tandem mass spectrometry is used to measure the kinetic energy dependent cross sections for reactions of the lanthanide metal gadolinium cation (Gd) and GdO with O and for collision-induced dissociation (CID) of GdO with Xe. Gd reacts with O in an exothermic and barrierless reaction to form GdO and O. GdO is also formed in this reaction, but this product ion is formed in a sequential reaction, as verified by pressure dependent measurements and comparison with the results for the reaction of GdO with O.

Gadolinium (Gd) Oxide, Carbide, and Carbonyl Cation Bond Energies and Evaluation of the Gd + O → GdO + e Chemi-Ionization Reaction Enthalpy.

Guided ion beam mass spectrometry (GIBMS) is used to measure the kinetic energy dependent product ion cross sections for reactions of the lanthanide metal gadolinium cation (Gd) with O, CO, and CO and for reactions of GdO with CO, O, and Xe. GdO is formed through barrierless and exothermic processes in the reactions of Gd with O and CO. All other reactions observed are endothermic, and analyses of their kinetic energy dependent cross sections yield 0 K bond dissociation energies (BDEs) for GdO, GdC, and GdCO.

The Ionic Hydrogen/Deuterium Bonds between Diammoniumalkane Dications and Halide Anions.

Halide-anion binding to 1,12-dodecanediammonium, tetramethyl-1,12-dodecanediammmonium, and tetramethyl-1,7-heptanediammonium has been investigated with infrared multiple-photon dissociation (IRMPD) spectroscopy in the 1000-2250 cm spectral region and with theory. Both charged ammonium groups in these diammonium compounds interact with the halide anion resulting in an ionic hydrogen bond (IHB) stretching frequency outside of the spectral frequency range that can be measured with the free-electron laser (FEL). This frequency is shifted into the spectral range upon exchanging all of the labile hydrogen atoms with deuterium atoms, thus making measurement of the ionic deuterium bond (IDB) stretching frequency possible.

Structure and energetics of gas phase halogen-bonding in mono-, bi-, and tri-dentate anion receptors as studied by BIRD.

Complexes of mono-, bi- (RB), and tridentate (RT) receptors with a range of anions (Cl(-), Br(-), I(-), NO3(-), H2PO4(-), HSO4(-), and tosylate (TsO(-))) have been studied in the gas phase by both experimental and theoretical methods. Temperature dependent blackbody infrared radiative dissociation (BIRD) experiments were performed on complexes of C8F17I with Br(-) and I(-), RB with I(-), NO3(-), HSO4(-), H2PO4(-), and TsO(-), and RT with I(-), HSO4(-) and TsO(-) and the observed Arrhenius parameters are reported here. Master equation modeling of the BIRD kinetics data was carried out to determine threshold dissociation energies.

Water-induced folding of 1,7-diammoniumheptane.

Effects of hydration on the gaseous structures of diprotonated 1,7-diaminoheptane and protonated heptylamine are investigated by infrared photodissociation (IRPD) spectroscopy and computational chemistry. IRPD spectra in the hydrogen bond stretching region (2800-3900 cm(-1)) indicate that 1,7-diammoniumheptane is linear and that hydration occurs predominantly by alternate solvation of the two protonated amine groups for clusters with up to 10 water molecules. The relative intensities of bonded versus free hydroxyl (OH) stretches are greater in the spectra of 1,7-diammoniumheptane with more than 12 water molecules attached than the corresponding reference spectra of heptylammonium.

Structures and energetics of electrosprayed uracil(n)Ca2+ clusters (n = 14-4) in the gas phase.

Clusters of uracil (U) about a calcium dication, U(n)Ca(2+) (n = 14-4), have been studied in the gas phase by both experimental and theoretical methods. Temperature dependent blackbody infrared radiative dissociation (BIRD) experiments were performed on U(n)Ca(2+) clusters with n = 14-5 and the observed Arrhenius parameters are reported here. Master equation modeling of the BIRD kinetics data was carried out to determine threshold dissociation energies.

Ions in size-selected aqueous nanodrops: sequential water molecule binding energies and effects of water on ion fluorescence.

The effects of water on ion fluorescence were investigated, and average sequential water molecule binding energies to hydrated ions, M(z)(H(2)O)(n), at large cluster size were measured using ion nanocalorimetry. Upon 248-nm excitation, nanodrops with ~25 or more water molecules that contain either rhodamine 590(+), rhodamine 640(+), or Ce(3+) emit a photon with average energies of approximately 548, 590, and 348 nm, respectively. These values are very close to the emission maxima of the corresponding ions in solution, indicating that the photophysical properties of these ions in the nanodrops approach those of the fully hydrated ions at relatively small cluster size.

Average sequential water molecule binding enthalpies of M(H2O)(19-124)2+ (M = Co, Fe, Mn, and Cu) measured with ultraviolet photodissociation at 193 and 248 nm.

The average sequential water molecule binding enthalpies to large water clusters (between 19 and 124 water molecules) containing divalent ions were obtained by measuring the average number of water molecules lost upon absorption of an UV photon (193 or 248 nm) and using a statistical model to account for the energy released into translations, rotations, and vibrations of the products. These values agree well with the trend established by more conventional methods for obtaining sequential binding enthalpies to much smaller hydrated divalent ions. The average binding enthalpies decrease to a value of ~10.

"Weighing" photon energies with mass spectrometry: effects of water on ion fluorescence.

We report a new, highly sensitive method for indirectly measuring fluorescence from ions with a discrete number of water molecules attached. Absorption of a 248 nm photon by hydrated protonated proflavine, PH(+)(H(2)O)(n) (n = 13-50), results in two resolved product ion distributions that correspond to full internal conversion of the photon energy (loss of approximately 11 water molecules) and to partial internal conversion of the photon energy and emission of a lower energy photon (loss of approximately 6 water molecules). In addition to fluorescence, a long-lived triplet state with a half-life of approximately 0.

Measuring internal energy deposition in collisional activation using hydrated ion nanocalorimetry to obtain peptide dissociation energies and entropies.

The internal energy deposited in both on- and off-resonance collisional activation in Fourier transform ion cyclotron resonance mass spectrometry is measured with ion nanocalorimetry and is used to obtain information about the dissociation energy and entropy of a protonated peptide. Activation of Na(+)(H(2)O)(30) results in sequential loss of water molecules, and the internal energy of the activated ion can be obtained from the abundances of the product ions. Information about internal energy deposition in on-resonance collisional activation of protonated peptides is inferred from dissociation data obtained under identical conditions for hydrated ions that have similar m/z and degrees-of-freedom.

Electron hydration and ion-electron pairs in water clusters containing trivalent metal ions.

The hydrated electron is one of the most fundamental nucleophiles in aqueous solution, yet it is a transient species in liquid water, making it challenging to study. The solvation thermodynamics of the electron are important for determining the band structure and properties of water and aqueous solutions. However, a wide range of values for the electron solvation enthalpy (-1.

Directly relating reduction energies of gaseous Eu(H2O)n(3+), n = 55-140, to aqueous solution: the absolute SHE potential and real proton solvation energy.

In solution, half-cell potentials are measured relative to other half-cells resulting in a ladder of thermodynamic values that is anchored to the standard hydrogen electrode (SHE), which is assigned an arbitrary value of exactly 0 V. A new method for measuring the absolute SHE potential is introduced in which reduction energies of Eu(H(2)O)(n)(3+), from n = 55 to 140, are extrapolated as a function of the geometric dependence of the cluster reduction energy to infinite size. These measurements make it possible to directly relate absolute reduction energies of these gaseous nanodrops containing Eu(3+) to the absolute reduction enthalpy of this ion in bulk solution.

Role of sequence in salt-bridge formation for alkali metal cationized GlyArg and ArgGly investigated with IRMPD spectroscopy and theory.

The roles of hydrogen bonding, electrostatic interactions, sequence, gas-phase basicity, and molecular geometry in determining the structures of protonated and alkali metal-cationized glycyl-L-arginine (GlyArg) and L-arginylglycine (ArgGly) were investigated using infrared multiple photon dissociation spectroscopy in the spectral range 900-1800 cm(-1) and theory. The IRMPD spectra clearly indicate that GlyArg x M(+), M = Li, Na, and Cs, form similar salt-bridge (SB) structures that do not depend significantly on metal ion size. In striking contrast, ArgGly x Li(+) exists in a charge-solvated (CS) form, whereas ArgGly x M(+), M = K and Cs, form SB structures.