Low-energy electron driven reactions in 2-bromo-5-nitrothiazole.

Thiazole derivatives are biologically relevant molecules, used also in pharmaceutical applications. Herein, we report results for electron attachment to 2-bromo-5-nitrothiazole (BNT) in the gas phase. Employing two crossed electron-molecule beam experiments, we determined the efficiency curves of various fragment anions as a function of the initial electron energy between about 0 and 10 eV as well as the emission angle and kinetic energy distributions of Br- and NO2- ions formed from a resonance near 4 eV.

X-ray absorption spectroscopy of FeH to aid its identification in astrochemical environments.

We present the first absorption spectrum of the unperturbed diatomic molecular ion FeH in any wavelength range. The cryogenic X-ray absorption spectrum at the L and L edge is consistent with an iron 3d occupation of 6.24e.

Imaging Dihydrogen Bond-Driven Assembly of Borazine on Au(111).

Dihydrogen bonding (DHB) is a peculiar type of attractive interaction occurring between a partially positively charged hydrogen atom and a partially negatively charged hydrogen atom. Borazine represents a prototypical molecule exhibiting dihydrogen bonding in both gas phase, as well as in its crystalline form. For borazine assemblies on solid surfaces, a direct observation and characterization of dihydrogen bonding has remained elusive, possibly due to an intricate interplay of substrate-molecule and intermolecular interactions.

Autodetachment of Diatomic Carbon Anions from Long-Lived High-Rotation Quartet States.

We show that strong molecular rotation drastically modifies the autodetachment of C_{2}^{-} ions in the lowest quartet electronic state a^{4}Σ_{u}^{+}. In the strong-rotation regime, levels of this state only decay by a process termed "rotationally assisted" autodetachment, whose theoretical description is worked out based on the nonlocal resonance model. For autodetachment linked with the exchange of six rotational quanta, the results reproduce a prominent, hitherto unexplained electron emission signal with a mean decay time near 3 ms, observed on stored C_{2}^{-} ions from a hot ion source.

Symmetry reduction induced by argon tagging gives access to low-lying excited states of FeH in the overtone region of the Fe-H stretching mode.

Iron is the most abundant transition metal in the interstellar medium (ISM), and is thought to be involved in a variety of astrochemical processes. Here, we present the infrared multiple photon dissociation (IRMPD) spectra of ArFeH and their deuterated isotopologues in the region of 2240-14 000 cm. The Fe-H overtone stretching mode in ArFeH and ArFeH is observed at 3636 ± 28 cm and 3659 ± 13 cm, respectively.

Plasmon-driven chemical transformation of a secondary amide probed by surface enhanced Raman scattering.

Plasmon-driven chemical conversion is gaining burgeoning interest in the field of heterogeneous catalysis. Herein, we study the reactivity of N-methyl-4-sulfanylbenzamide (NMSB) at nanocavities of gold and silver nanoparticle aggregates under plasmonic excitation to gain understanding of the respective reaction mechanism. NMSB is a secondary amide, which is a frequent binding motive found in peptides and a common coupling product of organic molecules and biomolecules.

Intersystem Crossing Control of the Nb + CO → NbO + CO Reaction.

The transfer of an oxygen atom from carbon dioxide (CO) to a transition metal cation in the gas phase offers atomic level insights into single-atom catalysis for CO activation. Given that these reactions often involve open-shell transition metals, they may proceed through intersystem crossing between different spin manifolds. However, a definitive understanding of such spin-forbidden reaction requires dynamical calculations on multiple global potential energy surfaces (PESs) coupled by spin-orbit couplings.

Formation of Doubly and Triply Charged Fullerene Dimers in Superfluid Helium Nanodroplets.

Sequential ionization of fullerene cluster ions (C_{60})_{n}^{+} within multiply charged helium nanodroplets leads to the intriguing phenomenon of forming and stabilizing doubly and triply charged fullerene oligomers. While the formation of doubly charged dimers (C_{60})_{2}^{2+} has been predicted in earlier studies, the observation of even triply charged ones (C_{60})_{2}^{3+} is highly surprising. This remarkable resilience against Coulomb explosion is achieved through efficient cooling within the superfluid environment of helium nanodroplets and a sequential ionization scheme that populates covalently bound or physisorbed fullerene dimers.

Zero-Point-Energy Driven Isotopic Exchange of the [HO] anion Probed by Mid-Infrared Action Spectroscopy.

We present the first observation of vibrational transitions in the [HO] anion, an intermediate in the anion-molecule reaction of water, HO, and hydride, H, using a laser-induced isotopic H/D exchange reaction action spectroscopy scheme applied to anions. The observed bands are assigned as the fundamental and first overtone of the HO-H vibrational stretching mode, based on anharmonic calculations within the vibrational perturbation theory and vibrational configuration interaction. Although the DO·D species has the lowest energy, our experiments confirm the DO·H isotope to be a sink of the H/D exchange reaction.

Master equation modeling of water dissociation in small ionic water clusters: Ag(HO) , = 4-6.

We model temperature-dependent blackbody infrared radiative dissociation (BIRD) rate coefficients of Ag(HO) , = 4-6, a system with loosely bound water molecules. We employ a master equation modeling (MEM) approach with consideration of absorption and emission of blackbody radiation, comparing single and multiple-well descriptions. The unimolecular dissociation rate coefficients are obtained using the Rice-Ramsperger-Kassel-Marcus (RRKM) theory, employing two approaches to model the sum of states in the transition state, the rigid activated complex (RAC) and the phase space limit (PSL) approach.

Dissociative Electron Attachment Dynamics of a Promising Cancer Drug Indicates Its Radiosensitizing Potential.

2-Bromo-1-(3,3-dinitroazetidin-1-yl)ethan-1-one (RRx-001) is a hypoxic cell chemotherapeutics with already demonstrated synergism in combined chemo-radiation therapy. The interaction of the compound with secondary low-energy electrons formed in large amounts during the physico-chemical phase of the irradiation may lead to these synergistic effects. The present study focuses on the first step of RRx-001 interaction with low-energy electrons in which a transient anion is formed and fragmented.

Multiconfigurational Character of Repulsive AΣ State Leaves Strong Signature in the Photodissociation Spectrum of Zn.

For the excitation to a repulsive state of a diatomic molecule, one expects a single broad peak in the photodissociation spectrum. For Zn, however, two peaks for the spin- and symmetry-allowed AΣ ← XΣ transition are observed. A detailed quantum-chemical analysis reveals pronounced multiconfigurational character of the AΣ state.

Dynamics of carbene formation in the reaction of methane with the tantalum cation in the gas phase.

The controlled activation of methane has drawn significant attention throughout various disciplines over the last few decades. In gas-phase experiments, the use of model systems with reduced complexity compared to condensed-phase catalytic systems allows us to investigate the intrinsic reactivity of elementary reactions down to the atomic level. Methane is rather inert in chemical reactions, as the weakening or cleavage of a C-H bond is required to make use of methane as C-building block.

Multistate Dynamics and Kinetics of CO Activation by Ta in the Gas Phase: Insights into Single-Atom Catalysis.

The activation of carbon dioxide (CO) by a transition-metal cation in the gas phase is a unique model system for understanding single-atom catalysis. The mechanism of such reactions is often attributed to a "two-state reactivity" model in which the high-energy barrier of a spin state correlating with ground-state reactants is avoided by intersystem crossing (ISC) to a different spin state with a lower barrier. However, such a "spin-forbidden" mechanism, along with the corresponding dynamics, has seldom been rigorously examined theoretically, due to the lack of global potential energy surfaces (PESs).

Master equation modeling of blackbody infrared radiative dissociation (BIRD) of hydrated peroxycarbonate radical anions.

Molecular cluster ions, which are stored in an electromagnetic trap under ultra-high vacuum conditions, undergo blackbody infrared radiative dissociation (BIRD). This process can be simulated with master equation modeling (MEM), predicting temperature-dependent dissociation rate constants, which are very sensitive to the dissociation energy. We have recently introduced a multiple-well approach for master equation modeling, where several low-lying isomers are taken into account.

Doubly charged dimers and trimers of heavy noble gases.

Many doubly charged heteronuclear dimers are metastable or even thermodynamically stable with respect to charge separation. Homonuclear dicationic dimers, however, are more difficult to form. He was the first noble gas dimer predicted to be metastable and, decades later, observed.

Magic cluster sizes of cationic and anionic sodium chloride clusters explained by statistical modeling of the complete phase space.

As one of the main components of sea salt aerosols, sodium chloride is involved in numerous atmospheric processes. Gas-phase clusters are ideal models to study fundamental physical and chemical properties of sodium chloride, which are significantly affected by the cluster size. Of particular interest are magic cluster sizes, which exhibit high intensities in mass spectra.

Ta and Nb + CO: intersystem crossing in ion-molecule reactions.

The reactions of Ta and Nb with CO proceed only by a highly efficient oxygen atom transfer reaction to the respective oxide at room temperature in the gas phase. Although the product spin states are not determined, thermochemistry dictates that they must be different from ground state quintet Ta and Nb, implying that intersystem crossing (ISC) has occurred. Recent reactive scattering experiments found dominant indirect dynamics for the reaction with Ta hinting at a bottleneck along the reaction path.

Hydrated Formic Acid Clusters and their Interaction with Electrons.

We investigate ion formation in hydrated formic acid (FA) clusters upon collision with electrons of variable energy, focusing on electron ionization at 70 eV (EI) and low-energy (1.5-15 eV) electron attachment (EA). To uncover details about the composition of neutral clusters, we aim to elucidate the ion formation processes in FA ⋅ W clusters initiated by interaction with electrons and determine the extent of cluster fragmentation.

Iron Complexes as Potential Carriers of Diffuse Interstellar Bands: The Photodissociation Spectrum of Fe(HO) at Optical Wavelengths.

The fullerene ion C is the only carrier of diffuse interstellar bands (DIBs) identified so far. Transition-metal compounds feature electronic transitions in the visible and near-infrared regions, making them potential DIB carriers. Since iron is the most abundant transition metal in the cosmos, we here test this idea with Fe(HO).

Gas-Phase Electronic Structure of Phthalocyanine Ions: A Study of Symmetry and Solvation Effects.

Research into and applications of phthalocyanines (Pc) are mostly connected to their intriguing electronic properties. Here, messenger-type UV-vis spectroscopy of two metal-free ions from the phthalocyanine family, cationic HPc and HPcD, along with their hydrates is performed. They show that the electronic properties of both ions can be traced to those in the conjugate base, Pc, however, they are affected by state splitting due to the reduced symmetry; in the HPc radical cation, a new band appears due to excitations into the singly-occupied molecular orbital.

Oxygen Radicals Entrapped between MgO Nanocrystals: Formation, Spectroscopic Fingerprints, and Reactivity toward Water.

Compaction of dehydroxylated MgO nanocrystal powders produces adsorbed oxygen radicals with characteristic UV-vis spectroscopic fingerprints. Identical absorption bands arise upon UV excitation in an oxygen atmosphere but in the absence of uniaxial pressure. Photophysical calculations on MgO gas-phase clusters reveal that the observed optical transitions at 4.

Spectroscopy of cluster aerosol models: IR and UV spectra of hydrated glyoxylate with and without sea salt.

Glyoxylic acid is formed in the troposphere by oxidation of organic molecules. In sea salt aerosols, it is expected to be present as glyoxylate, integrated into the salt environment and strongly interacting with water molecules. In water, glyoxylate is in equilibrium with its -diol form.

Spectroscopy of C60+ and C120+ in the mid-infrared.

Infrared spectra of C60+ and C120+, obtained via helium messenger spectroscopy, are reported. For C60+, new absorption features have been found just above the discrete vibrational spectrum of the ion. The absorption profile, which is broad and contains little structure, is assigned to one or more electronic absorption transitions and is in good agreement with predictions from time-dependent density functional theory.