Cyclotrimerization of Acetylene under Thermal Conditions: Gas-Phase Kinetics of V and Fe + CH.

The kinetics of successive reactions of acetylene (CH) initiated on either vanadium or iron atomic cations have been investigated under thermal conditions using the variable-ion source and temperature-adjustable selected-ion flow tube apparatus. Consistent with the literature results, the reaction of Fe + CH primarily yields Fe(/ = (CH)); however, analysis via quantum chemical calculations and statistical modeling shows that the mechanism does not form benzene upon the third acetylene addition. The kinetics are more consistent with successive addition of three acetylene molecules, yielding Fe(CH), followed by an addition of a fourth acetylene molecule, initiating cyclotrimerization, yielding either Fe(CH) + neutral benzene or Fe(Bz) + acetylene, where Bz is a benzene ligand.

Infrared spectroscopy of the protonated HCl dimer and trimer.

The protonated HCl dimer and trimer complexes were prepared by pulsed discharges in supersonic expansions of helium or argon doped with HCl and hydrogen. The ions were mass selected in a reflectron time-of-flight spectrometer and investigated with photodissociation spectroscopy in the IR and near-IR regions. Anharmonic vibrational frequencies were computed with VPT2 at the MP2/cc-pVTZ level of theory.

Electronic structure of NdO via slow photoelectron velocity-map imaging spectroscopy of NdO.

Electronically excited NdO is a possible product of the chemistry associated with the release of Nd into the ionosphere, and emission from these states may contribute to the observations following such experiments. To better characterize the energetics and spectroscopy of NdO, we report a combined experimental and theoretical study using slow photoelectron velocity-map imaging spectroscopy of cryogenically cooled NdO anions (cryo-SEVI) supplemented by wave function-based quantum-chemical calculations. Using cryo-SEVI, we measure the electron affinity of NdO to be 1.

Gas-Phase Anionic Metal Clusters are Model Systems for Surface Oxidation: Kinetics of the Reactions of with O (M = V, Cr, Co, Ni; = 1-15).

The reactions of anionic metal clusters with O (M = V ( = 1-15), Cr ( = 1-15), Co ( = 1-12), and Ni ( = 1-14)) are investigated from 300 to 600 K using a selected-ion flow tube. All rate constants show a positive temperature dependence, well described by an Arrhenius equation. Rate constants exceed (or are extrapolated to exceed at higher temperatures) the Langevin-Gioumousis-Stevenson capture rate constant.

Infrared spectroscopy of H(CO) in the gas phase and in para-hydrogen matrices.

The H(CO) and D(CO) molecular ions were investigated by infrared spectroscopy in the gas phase and in para-hydrogen matrices. In the gas phase, ions were generated in a supersonic molecular beam by a pulsed electrical discharge. After extraction into a time-of-flight mass spectrometer, the ions were mass selected and probed by infrared laser photodissociation spectroscopy in the 700 cm-3500 cm region.

Barrierless methane-to-methanol conversion: the unique mechanism of AlO.

The kinetics of AlO+ + CH4 are studied from 300-500 K using a selected-ion flow tube. At all temperatures the reaction proceeds near the Langevin-Gioumousis-Stevenson collision rate with two product channels: hydrogen atom abstraction (AlOH+ + CH3, 86 ± 5%) and methanol formation (Al+ + CH3OH, 14 ± 5%). Density functional calculations show the key Al-CH3OH+ intermediate is formed barrierlessly via a mechanism unique to aluminum, avoiding the rate-limiting step common to other MO+.

The Role of Tunneling in the Spectra of H and D up to 7300 cm.

The spectra for H and D are extended to cover the region between 4830 and 7300 cm. These spectra are obtained using mass-selected photodissociation spectroscopy. To understand the nature of the states that are accessed by the transitions in this and prior studies, we develop a four-dimensional model Hamiltonian.

Catalytic Oxidation of CO by NO Enabled by AlO: Temperature Dependent Kinetics and Statistical Modeling.

The reactions of AlO + NO and AlO + CO, forming a catalytic cycle oxidizing CO by NO, have been investigated from 300 to 600 K in a variable ion source, temperature adjustable, selected-ion flow tube (VISTA-SIFT). Reaction coordinates have been calculated using density functional theory and statistical modeling of those surfaces compared to experimental kinetics data for mechanistic insight. The reaction of AlO + NO proceeds at the Su-Chesnavich collisional limit at all temperatures studied, yielding only AlO, with the exception of a small (<5%) amount of association product, AlO(NO) at 300 K.

Redefining the Mechanism of O Etching of Al Superatoms: An Early Barrier Controls Reactivity, Analogous to Surface Oxidation.

New insights into aluminum anion cluster reactivity with O were obtained through temperature-dependent kinetics measurements. Overall reactivity is controlled by a barrier at an avoided crossing where charge is transferred from the cluster to the O, mechanistically similar to what occurs as O approaches a bulk Al surface. Contrary to prior interpretations, spin conservation does not inhibit the reaction of clusters with an odd number of Al atoms.

Quantifying the Competition between Intersystem Crossing and Spin-Conserved Pathways in the Thermal Reaction of V + NO.

The kinetics of V + NO and VO + NO are studied using a selected-ion flow tube from 300-600 K at pressures of 0.25-0.70 Torr helium.

Mid-Infrared Spectroscopy of CH Isomers in the Gas Phase: Benzylium and Tropylium.

Both prominent CH isomers, the benzylium and the tropylium cations, were generated in an electrical discharge/supersonic expansion from toluene and cycloheptatriene precursors. Their infrared spectra were measured in the region of 1000-3500 cm using photodissociation of the respective argon- and nitrogen-tagged complexes with a broadly tunable OPO/OPA laser system. Spectral signatures of both isomers were observed independent of the precursor, albeit in different relative intensities.

Communication: Infrared photodissociation spectroscopy of the H cation in the gas phase.

The H cation was generated in a pulsed-discharge supersonic expansion of hydrogen and mass-selected in a time-of-flight spectrometer. Its vibrational spectrum was measured in the region of 2050-4550 cm using infrared photodissociation with a tunable OPO/OPA laser system. The H photodissociates, producing H, H, and H fragments; each of these fragment channels has a different spectrum.

Temperature and Isotope Dependent Kinetics of Nickel-Catalyzed Oxidation of Methane by Ozone.

The temperature dependent kinetics of Ni + O and of NiO + CH/CD are measured from 300 to 600 K using a selected-ion flow tube apparatus. Together, these reactions comprise a catalytic cycle converting CH to CHOH. The reaction of Ni + O proceeds at the collisional limit, faster than previously reported at 300 K.

Spectroscopy of Proton Coordination with Ethylenediamine.

Protonated ethylenediamine monomer, dimer, and trimer were produced in the gas phase by an electrical discharge/supersonic expansion of argon seeded with ethylenediamine (CHN, en) vapor. Infrared spectra of these ions were measured in the region from 1000 to 4000 cm using laser photodissociation and argon tagging. Computations at the CBS-QB3 level were performed to explore possible isomers and understand the infrared spectra.

An Argon-Oxygen Covalent Bond in the ArOH Molecular Ion.

The OH cation is a well-known diatomic for which the triplet ( Σ ) ground state is 50.5 kcal mol more stable than its corresponding singlet ( Δ) excited state. However, the singlet forms a strong donor-acceptor bond to argon with a bond energy of 66.

Cryo IR Spectroscopy of N and H on Ru: The Effect of N on the H-Migration.

We present the cryo IR-PD spectra of the coadsorbed [Ru(H)(N)] and [Ru(N)(H)] species differing in the adsorption sequence of H and N, which we record via application of tandem cryo ion trapping. We observe strong evidence for dissociative H adsorption, and the spectra reveal differences in the Ru-H stretching region, which we assign to distal and proximal hydrogen atom locations on the Ru cluster, their migration likely hindered by preloaded nitrogen molecules and unaffected by subsequent N adsorption.

Infrared Spectroscopy of the Astrochemically Relevant Protonated Formaldehyde Dimer.

The protonated formaldehyde dimer (HCO)H was generated in an electrical discharge and supersonic expansion of argon saturated with formalin solution vapor. Its infrared spectrum was measured in the region from 900 to 4000 cm employing infrared laser photodissociation and messenger atom tagging. Comparison of the experiment to quantum chemical computations at the CCSD(T)/cc-pVQZ//MP2/cc-pVTZ level reveals that the experimentally observed structure is the head-to-tail dimer and not the more stable proton-bound dimer.

Near-infrared spectroscopy and anharmonic theory of the HOAr cation complexes.

Weakly bound complexes of the water radical cation with argon (HOAr, n = 1,2) were generated by an electrical discharge/supersonic expansion and probed with mid- and near-infrared photodissociation spectroscopy in the 2050-4550 and 4850-7350 cm regions. To elucidate these spectra, these complexes were studied computationally at the CCSD(T) level including anharmonicity with the VPT2 method. The comparison between experiment and predicted spectra demonstrates that the VPT2 method is adequate to capture most of the vibrational band positions and their intensities.

Discrepancy Between Experimental and Theoretical Predictions of the Adiabaticity of Ti +CH OH.

The reaction between Ti and methanol (CH OH) is a model system for competition between activation of C-O, C-H, and O-H bonds and of the role of excited electronic pathways in catalytic processes. Herein, we use experimental kinetics, quantum chemical calculations, and statistical modeling to identify the critical features of the reaction's potential energy surface. Experimental kinetics data between 300 and 600 K shows the reaction largely proceeds through C-O bond activation, yielding TiOH and TiO .