We studied the photoionization of 2-pyridone and its tautomer, 2-hydroxypyridine by means of VUV synchrotron radiation coupled to a velocity map imaging electron/ion coincidence spectrometer. The photoionization efficiency (PIE) spectrum is composed of steps. The state energies of the [2-pyridone]⁺ cation in the ground and à excited electronic states, as well as of the [2-hydroxypyridine]⁺ cation in the electronic ground state, are determined. The slow photoelectron spectra (SPES) are dominated by the 0⁰ ₀ transitions to the corresponding electronic states together with several weaker bands corresponding to the population of the pure or combination vibrational bands of the cations. These vibrationally-resolved spectra compare very well with state-of-the-art calculations. Close to the ionization thresholds, the photoionization of these molecules is found to be mainly dominated by a direct process whereas the indirect route (autoionization) may contribute at higher energies.

Investigations of the spectroscopy and dynamics of small- and medium-sized molecules and clusters represent a hot topic in atmospheric chemistry, biology, physics, atto- and femto-chemistry and astrophysics.

Herein we present the results of a blind challenge to quantum chemical methods in the calculation of dimerization preferences in the low temperature gas phase. The target of study was the first step of the microsolvation of furan, 2-methylfuran and 2,5-dimethylfuran with methanol. The dimers were investigated through IR spectroscopy of a supersonic jet expansion. From the measured bands, it was possible to identify a persistent hydrogen bonding OH–O motif in the predominant species. From the presence of another band, which can be attributed to an OH-π interaction, we were able to assert that the energy gap between the two types of dimers should be less than or close to 1 kJ/mol across the series. These values served as a first evaluation ruler for the 12 entries featured in the challenge. A tentative stricter evaluation of the challenge results is also carried out, combining theoretical and experimental results in order to define a smaller error bar. The process was carried out in a double-blind fashion, with both theory and experimental groups unaware of the results on the other side, with the exception of the 2,5-dimethylfuran system which was featured in an earlier publication.

Three oxygen-containing gas-phase diatomic trications ReO³⁺, NbO³⁺ and HfO³⁺ as well as the diatomic tetracation NbO⁴⁺ have been observed by mass spectrometry at non-integer m/z values. These unusual triply charged molecular ion species, together with the corresponding diatomic dications ReO²⁺, NbO²⁺ and HfO²⁺, were produced by energetic, high-current oxygen (¹⁶O⁻) ion beam sputtering of rhenium, niobium and hafnium metal samples, respectively, whose surfaces were dynamically oxidized by oxygen primary ion incorporation. In addition, NbO^z+ (z ≤ 4) were generated by intense femtosecond laser excitation and photofragmentation (Coulomb explosion) of Nb_xO_yclusters and were detected through Time-of-Flight Mass Spectrometry (TOF). Our experimental results confirm previous reports on the detection of NbO⁴⁺, NbO³⁺, NbO²⁺, HfO³⁺ and HfO²⁺ with Atom Probe mass spectrometry, whereas ReO³⁺ and ReO²⁺ apparently had not been observed before. In addition, these multiply charged molecular ions have been studied theoretically for the first time. Ab initio calculations of their electronic structures show that the diatomic trications ReO³⁺, NbO³⁺ and HfO³⁺ are long-lived metastable gas-phase species, with bond lengths of 1.61 Å, 1.62 Å and 1.86 Å, respectively. They present large potential barriers with respect to dissociation of more than 2.7 eV. The corresponding diatomic dications are thermochemically stable molecules with very large dissociation energies (>3.5 eV). Our calculations predict the diatomic tetracation ReO⁴⁺ to be a metastable ion species in the gas phase. We compute a potential barrier toward fragmentation of 0.6 eV; its formation requires a quadruple adiabatic ionization energy of 85.7 eV. Even though our calculations show that NbO⁴⁺ is a weakly bound (dissociation barrier ∼0.1 eV) metastable molecule, it is here identified via linear time-of-flight mass spectrometry.

Electrode–electrolyte microscopic interfacial studies are of great interest for the design and development of functional materials for energy storage and catalysis applications. First-principles-based simulation methods are used here to understand the structure, stability, energetics, and microscopic adsorption mechanism of various hydrophilic and hydrophobic ionic liquids (ILs; 1-butyl 3-methylimidazolium [BMIm]⁺[X]⁻, where X = Cl, DCA, HCOO, BF₄, PF₆, CH₃SO₃, OTF, and TFSA) interacting with a metallic surface. We have selected the Au(111) surface as a potential electrode model, and our computations show that ILs (anions and cations) adsorb specifically at some selective adsorption sites. Indeed, hydrophilic anions of ILs are strongly adsorbed on the gold surface (via Au–Cl and Au–N bonds at Au(111)), whereas hydrophobic anions are weakly bonded. The [BMIm]⁺ is always found to be stabilized parallel to the metal surface, irrespective of the nature of the anion, through various kinds of noncovalent interactions. Mulliken, Löwdin, and Hirshfeld charge analyses reveal that there is significant charge transfer between ILs and the surface that may enhance the charge transfer mechanism between the surface and electrolytes for electrochemical applications. Our study shows that the electrostatic and van der Waals interactions are in action at these interfaces. Moreover, we show that there are several covalent and noncovalent interactions between ILs and the metal surface. These interactions play an essential role to maintain the electrostatic behaviors at the solid–liquid interface. The present findings can be helpful to predict specific selectivity and subsequent design of materials for energy harvesting and catalysis applications.