Gold monolayer protected clusters (MPCs) are a class of quantum-confined metal nanostructures that span the transition from molecular to metallic electron dynamics. MPCs are well-described by three structural motifs that include (i) an all-metal atom core, (ii) an inorganic semiring of alternating Au-S staple units, and (iii) passivating organic ligands. The structure and composition of these domains influence the nanocluster optical and electronic properties, providing a well-defined platform to elucidate structure-dependent energy relaxation mechanisms in quantum confined metals. In this presentation, ultrafast electronic and charge carrier relaxation will be discussed. Coherent two-dimensional electronic spectroscopy (2DES) provides an excitation-detection frequency-frequency correlation by spreading the transient signal over two axes that spectrally and temporally resolves state-to-state electron dynamics on the femtosecond timescale. Here, 2DES was used to distinguish several electronic fine-structure peaks that comprise a charge transfer resonance in molecular-like Au₃₈(SC₆H₁₃)₂₄ nanoclusters. By manipulating the polarization vector of the femtosecond pulses, additional insights on the coupling of transition dipole moments were obtained from cross-peak specific spectra. These results revealed a low-amplitude excited state absorption signal that uniquely relaxed through a charge transfer resonance within 150 femtoseconds. Evidence of population changes of excited vibrational states within the electronic manifold, which undergo intramolecular vibrational relaxation (IVR), were quantified by fitting time-dependent amplitudes of 2DES-detected cross-peaks spanning a frequency range of 1000 cm⁻¹. Anisotropy and orientation parameters obtained from polarization-selective 2DES were applied to better understand state-specific relaxation through coupled electronic states. Solvent dependences on charge carrier relaxation will be discussed. These results demonstrate the ability of polarization-selective 2DES to map state-resolved electron dynamics in molecular-like metal nanoclusters.

Beryllium is known to be a challenging test for even high level ab initio methods due to high electron correlation contributions. There is fundamental interest in understanding how well computational methods can predict physical properties of beryllium containing molecules, but very little available experimental data on these molecules. We have continued in our exploration of pure beryllium clusters, and have acquired preliminary spectra for the beryllium pentamer Be₅. In this talk we will present our work to date on Be₅, with comparisons to theory and the Beryllium tetramer

In the world of single molecule magnets (SMMs), lanthanide-based single molecule magnets have proven to be potential source of strong anisotropic magnetic moments and recent research has sought to harness these properties in the creation of SMMs with long spin relaxation lifetimes and high blocking temperatures. The properties of these lanthanide SMMs are dictated by both the lanthanide identity as well as the structure of the magnetic core, and SMMs with odd-numbers of metal centers have been seen to exhibit exciting magnetic properties such as spin frustration and toroidal spin moments. Expanding on previous studies of bimetallic lanthanide oxide clusters we employ anion photoelectron spectroscopy and computational modelling of gas-phase Ln₃O⁻ (Ln = Ce, Sm, Gd) clusters to better understand the effects of spin strain on the electronic and magnetic properties of ligand-free SMM cores. Spectra exhibit the typical binding energies of lanthanide oxide clusters (between 0.7eV and 1.2 eV) and photoelectron angular distribution anomalies we attribute to interactions between departing photoelectrons and remnant neutral clusters are observed.

As the global energy landscape currently dominated by the fossil fuels is causing environmental and energy issues, there is an urgent need to shift to renewable energy sources. Production of Hydrogen gas a source of energy from water is by far the cleanest renewable energy source. Transition metal oxides are effective catalysts for the hydrogen evolution reaction. Small metal oxide clusters are used as a model to understand the catalytically active sites in bulk. In this study we use anion photoelectron spectroscopy as a means of understanding the electronic structure of the anionic and neutral species of the Zinc oxide clusters.

Rovibrational spectra of N₂-H₂O van der Waals complexes were measured in the overtone range, around the 2 OH stretching regions. The rotationally resolved (ν₁′,ν₂′,ν₃′) ← (ν₁",ν₂",ν₃") = (2,0,0) ← (0,0,0) and (1,0,1) ← (0,0,0) vibrational bands were observed; where ν₁, ν₂, ν₃ are the vibrational quantum numbers of the isolated water molecule. As well, a combination band involving the (1,0,1) state and the intermolecular in-plane N₂ bending vibration will be presented. The spectra were measured using continuous wave cavity ringdown spectroscopy in a supersonic expansion, as implemented in the FANTASIO+ setup [1,2]. These spectra were analyzed by considering the feasible tunneling motions of this complex, fitted as separate asymmetric rotors for the four observed tunneling states. The tunneling splittings are discussed as a function of the vibrational state and compared with other isotopologues. The assignment of a rovibrational perturbation will also be discussed.
[1] M. Herman, K. Didriche, D. Hurtmans, B. Kizil, P. Macko, A. Rizopoulos, P.V. Poucke, Molecular Physics, 2007, 105 (5-7), 815-823. [2] A.S. Bogomolov, A. Roucou, R. Bejjani, M. Herman, N. Moazzen-Ahmadi, C. Lauzin, Chemical Physics Letters, 2021, 774, 138606.

Structural calculations and high-resolution infrared spectra are reported for trimers and tetramers containing CO₂ together with CO and/or N₂. Among the 9 clusters studied here, only (CO₂)₂-CO was previously observed by high-resolution spectroscopy. The spectra, which occur in the region of the ν₃ fundamental of CO₂ (~2350 cm⁻¹), were recorded using a tunable optical parametric oscillator source to probe a pulsed supersonic slit jet expansion. The trimers (CO₂)₂-CO and (CO₂)₂-N₂ have structures in which the CO or N₂ is aligned along the symmetry axis of a staggered side-by-side CO₂ dimer unit. The observation of two fundamental bands for (CO₂)₂-CO and (CO₂)₂-N₂ shows that this CO₂ dimer unit is non-planar, unlike (CO₂)₂ itself. For the trimers CO₂-(CO)₂ and CO₂-(N₂)₂, the CO or N₂ monomers occupy equivalent positions in the ‘equatorial plane’ of the CO₂, pointing toward its C atom. To form the tetramers CO₂-(CO)₃ and CO₂-(N₂)₃, a third CO or N₂ monomer is then added off to the ‘side’ of the first two. In the mixed tetramers CO₂-(CO)₂-N₂ and CO₂-CO-(N₂)₂, this ‘side’ position is taken by N₂ and not CO. In addition to the fundamental bands, combination bands are also observed for (CO₂)₂-CO, CO₂-(CO)₂, and CO₂-(N₂)₂, yielding some information about their low-frequency intermolecular vibrations.

The interaction preferences of water with small molecules has been an area of interest for many years as we endeavor to better understand solvation at the molecular scale. Here, a study of weakly-bound complexes of γ-lactones with water is presented. In this study, matrix isolation FTIR and computational methods were used to examine stable 1:1 complexes of γ-butyrolactone, γ-valerolactone, and Angelica lactone complexes with water. These five-membered heterocycles contain multiple regions that could serve as binding sites for a single water molecule including two chemically distinct oxygen atoms and a π-cloud. Matrix isolation FTIR experiments identified several peaks that were not associated with isolated water or lactone, implying the bands are due to weakly-bound complexes of the two. In addition to normal water, and HDO complexes with the lactones were also observed. The spectra can be interpreted with the aid of computational chemistry. In this work, multiple density functional theories along with MP2 calculations were used to find minimum energy configurations and vibrational structure of the complexes that can be directly compared to our spectra. Possible interpretations of the experimental and computational results are presented.

Polycyclic aromatic hydrocarbons are considered as primary carriers of the unidentified interstellar bands. The recent discovery of the first interstellar aromatic molecule, benzonitrile (C₆H₅CN), suggests a repository of aromatic hydrocarbons in the outer earth environment. Herein, we report an infrared (IR) study of benzonitrile–(D₂O)_n clusters using mass-selective detection in helium nanodroplets. In this work, we use isotopically substituted water, D₂O, instead of (H₂O) because of our restricted IR frequency range (2565–3100 cm⁻¹). A comparison of the experimental and predicted spectra computed at the MP2/6-311++G(d,p) level of benzonitrile–(water)_1–2 clusters reveals the formation of a unique local minimum structure, which was not detected in previous gas-phase molecular beam experiments. Here, the solvent water forms a nearly linear hydrogen bond (H-bond) with the nitrile nitrogen of benzonitrile, while the previously reported most stable cyclic H-bonded isomer is not observed. This can be rationalized by the stepwise aggregation process of precooled monomers. The addition of a second water molecule results in the formation of two different isomers. In one of the observed isomers, a H-bonded water chain binds linearly to the nitrile nitrogen similar to the monohydrated benzonitrile–water complex. In the other observed isomer, the water dimer forms a ring-type structure, where a H-bonded water dimer simultaneously interacts with the nitrile nitrogen and the adjacent ortho CH group. Finally, we compare the water-binding motif in the neutral benzonitrile–water complex with the corresponding positively and negatively charged benzonitrile–water monohydrates to comprehend the charge-induced alteration of the solvent binding motif.

Formic acid is the simplest carboxylic acid and plays a pivotal role in atmospheric chemistry. It is an intermediate in the Water-Gas-Shift reaction, decomposing into either CO₂ and H₂ or into H₂O and CO under ionizing radiation. Furthermore, it is important in acid rain and seeding the nucleation of water molecules in cloud formation. Here, I will present our recent work, where femtosecond lasers are applied to study the microsolvation and photodynamics of molecular gas-phase formic acid-water clusters using time-of-flight mass spectrometry. Our cluster distribution confirms the enhanced stability of (FA)₅(H2O)₁H⁺, where the formic acid cluster forms a cage-like structure surrounding the water molecule. Upon exposure to high laser intensities (400 nm, 200 fs, laser intensities of 1.9x10¹⁵ W/cm²), the clusters undergo an enhanced ionization which produces multiply charged ions of C, O, and CO. Coulomb explosion of these ions leads to a large kinetic energy release that is shown to increase with the size of clusters. The measured values are in agreement with a Molecular Dynamics simulation of the Coulomb explosion for the mean size of the clusters within the cluster distribution, suggesting that no movement occurs during ionization. Of particular relevance, we record a large amount of signal for the carbon monoxide trication. KER values were recorded as high as 44 eV for CO³⁺ for (FA)₂, but increases to 75.3 eV when the cluster distribution is shifted toward (FA)₅ as the largest signal. Potential energy curves for CO³⁺ are calculated using the multireference configuration interaction (MRCI+Q) method to confirm the existence of metastable states with a large potential barrier with respect to dissociation. This combined experimental and theoretical effort confirms the existence of metastable CO³⁺.