As well known, water and oil do not mix with each other. To investigate the intermolecular interaction between water and oil, the nonane-water (1:1) cluster is investigated by infrared spectroscopy and theoretical calculation. Both symmetric and antisymmetric stretch bands of water in the cluster shows the  20 cm-1 low frequency shift from those of a bare water molecule. In the simulated stable structures of the cluster, the OH bond of the water molecule orients to a carbon atom of the nonane molecule. These experimental and theoretical results imply the formation of the unconventional OH...C hydrogen bond in the nonane-water cluster. This OH...C hydrogen bond is theoretically confirmed by the FMO-PIEDA analysis. The unconventional OH...C hydrogen bond in the nonane-water cluster is discussed with these spectroscopic observation and theoretical calculations.

Motivated by a large dynamical nuclear polarization effect observed for nitroxyl radicals combined with halogenated solvents [1] and the investigation of the microsolvation of TEMPO in the gas phase by Brás et. al. [2][3] the present work investigates the microsolvation of TEMPO by benzyl alcohol and its halogenated derivatives [4]. Considering possible hydrogen bonding, the OH stretching vibration of the alcohol is used as a sensitive indicator for the presence of a specific heterodimer (1:1) conformation by comparing slit jet FTIR-spectra with the results of harmonic DFT calculations. By varying the halogenation of the alcohols the role of polarity and polarizability for the conformational solvation preferences is explored. For the combination of TEMPO with benzyl alcohol, two signals of 1:1-complexes can be observed and assigned. Switching to halogenated benzyl alcohols with chlorine, bromine or iodine at the para-position these signals are also visible but slightly shifted to lower wavenumbers which agrees with the DFT calculations. To get more insight into steric effects TEMPO was also paired with ortho-halogenated benzyl alcohols. For the chlorine and bromine substitution a clear preference for one binding pattern was observed which was also predicted by theory. [1] G. Liu, M. Levien, N. Karschin, G. Parigi, C. Luchinat, M. Bennati, Nat. Chem. 9 (2017) 676. [2] E. M. Brás, T. L. Fischer, M. A. Suhm, Angew. Chem. Int. Ed. 60 (2021) 19013. [3] E. M. Brás, C. Zimmermann, R. Fausto, M. A. Suhm, Angew. Phys. Chem. Chem. Phys. 26 (2024) 5822. [4] M. Lange, E. Sennert, M. A. Suhm, Synlett 33 (2022) 2004.

Cold rare gas quantum matrices are commonly used in vibrational spectroscopy to immobilize molecular clusters and to simplify their IR spectra by reduction of the rotational structure and suppression of hot vibrational transitions. Among all types of solid rare gas cryomatrices, Ne matrices are known for causing particularly small redshifts of vibrational wavenumbers.
This subtle perturbation of H-bond vibrations is scrutinized by discussing a data pair compilation of hydride stretching frequencies of H-bonded dimers measured in Ne matrices [1] and supersonic jet expansions. By doing so, we encounter systematic trends and outliers within and across various substance classes. Some outliers may be related to anharmonic effects, as recently reported for ketones [2] and tertiary amines [3]. A particular focus will be on nitrogen acceptors such as amines and nitriles, and more generally on water complexes which are of interest for spectroscopic benchmark experiments [4].
Robust correlations between gas phase and matrix wavenumbers could provide a powerful tool for isomer and resonance assignments in IR spectra and also for predictions of cold gas phase wavenumbers based on more sensitive matrix experiments. Additionally, this study may serve as a base for future theoretical studies and benchmarking projects on subtle matrix effects.
[1] D. Mihrin, A. Voute, P. W. Jakobsen, K. L. Feilberg, R. W. Larsen, J. Chem. Phys. 156 (2022) 084305 [2] T. L. Fischer, T. Wagner, H. C. Gottschalk, A. Nejad, M. A. Suhm, J. Phys. Chem. Lett. 12 (2021) 138-144 [3] E. Lwin, T. L. Fischer, M. A. Suhm, J. Phys. Chem. Lett. 14 (2023) 10194-10199 [4] T. L. Fischer, M. Bödecker, S. M. Schweer et. al., Phys. Chem. Chem. Phys. 25 (2023) 22089-22102.

When an OH group forms a hydrogen bond (H-bond), its stretching vibration band shows a characteristic red-shift. It has been predicted that such an OH stretch frequency shift, ∆ν_OH, on H-bond formation linearly correlates with its enthalpy change, ∆H. This is called Badger-Bauer rule. Studies on the Badger-Bauer rule have been focused on singly H-bonded pairs, and experimental confirmation for H-bonded network systems, in which multiple H-bonds cooperatively work, has been very scarce. In the present study, we performed infrared spectroscopy of H⁺(methanol)_n-benzene (n=2-7) clusters in the gas phase T. Kato and A. Fujii, Phys. Chem. Chem. Phys. 24, 163 (2022).^,T. Kato and A. Fujii, Phys. Chem. Chem. Phys. 25, 30188 (2023). We show a good linear correlation between

ν

_OH of the terminal methanol site weakly −hydrogen bonded with benzene and the enthalpy change in clustering of H^+(MeOH)_n to H^+(MeOH)_n+1 T. Kato and A. Fujii, Phys. Chem. Chem. Phys. 25, 30188 (2023)..M. S. El-Shall et al., J. Phys. Chem. 96, 2045 (1992)..

The hydrogen-bonded complexes between 2-naphthol (or β-naphthol) and anisole are explored by detecting their IR absorption in the OH stretching range as well as their UV absorption by means of laser-induced fluorescence and resonance-enhanced two-photon UV ionisation. For the more stable cis and the metastable trans conformations of the OH group in 2-naphthol, hydrogen bonding to the oxygen atom of anisole is consistently detected in different supersonic jet expansions. Alternative hydrogen bonding to the aromatic ring of anisole remains elusive, although the majority of state-of-the-art hybrid DFT functionals with London dispersion correction and - less surprisingly - MP2 wavefunction theory predict it to be slightly more stable at zero-point level, unless three-body dispersion correction is added to the B3LYP-D3(BJ) approach. This changes at the CCSD(T) level, which forecasts an energy advantage of 1-3 kJ mol⁻¹ for the classical hydrogen bond arrangement even after including (DFT) zero-point energy contributions. The UV and IR spectra of the cis complex exhibit clear evidence for intensity redistribution of the primary OH stretch oscillator to combination states with the same low frequency intermolecular bending mode by Franck-Condon-type vertical excitation mechanisms. This rare case of dual (vibronic and vibrational) Franck-Condon activity of a low-frequency mode invites future studies of homologues where aromatic ring docking of the OH group may be further stabilised, e.g. through anisole ring methylation.H. C. Gottschalk et al., Angew. Chem. Int. Ed. 2016, 55, 1921-1924html:<hr /><h3>Footnotes: H. C. Gottschalk et al., Angew. Chem. Int. Ed. 2016, 55, 1921-1924

Determining geometric structures of ion-molecule complexes and unravelling intermolecular interactions within complexes are key steps for gaining deep insights into chemical reactions and intrinsic mechanisms. Our study focuses on a catalytic system involving hexafluoroisopropanol (HFIP) as both solvent and catalyst, in conjunction with hydrogen peroxide (H₂O₂) as an oxidant, which has garnered significant attention in organic synthesis. We employed size-selective, negative ion photoelectron spectroscopy in conjunction with quantum chemical calculations to investigate the geometric and electronic structures of [HFIP₋H•H₂O₂]⁻, a quintessential complex in this catalytic olefin epoxidation system. Our study indicates an unexpected prevalent existence of an energetically high-lying isomer of this complex. The combination of two theoretical properties on the molecular surfaces revealed an influential direction-specific effect in the course of complexation, providing an extraordinary rationale on how the two components dock together that ultimately leads to the formation of a high-lying isomer. Furthermore, our study extends beyond anionic complexes to explore the nature of interactions between CO₂ molecules and cationic scandium oxides of varying sizes. The binding strength shows a decreasing trend with increasing size of oxide cations, while the orientation of CO₂ molecules relative to metal sites exhibits significant variations. The analyses based on well-accepted electrostatic considerations, however, failed to provide satisfactory explanations for the binding patterns. Quantitative energy decomposition analysis revealed that both electrostatic attractions and orbital interactions are indispensable for CO₂ adsorption on cationic scandium oxides. The introduction of a theoretical descriptor that takes orbital interactions into account provides a comprehensive explanation not only for the binding strength but also for the complex orientation. Overall, our findings contribute significantly to the fundamental understanding of non-covalent intermolecular interactions and provide valuable insights for the rational design and optimization of catalytic systems for various applications.

Carbon cluster cations (C_n⁺, n = 13 – 20) were investigated using tunable laser photodissociation spectroscopy in the ultraviolet region to probe their electronic states. These clusters were mass-selected after being produced via laser vaporization of a carbon rod in an inert gas expansion. Due to the abundance of carbon in space, these findings were utilized to evaluate the potential of these clusters as carriers of unidentified spectral features and to examine their possible astrochemical relevance. To complement the experimental results, computational studies using density functional theory were performed to gain insight into the geometries, dissociation energies, and electronic transition assignments of these clusters. As a result of their strong multireference character caused by multiple low-lying excited states, these carbon cluster cations provide an interesting challenge for theory.

Lanthanides have been actively explored as the basis for single molecule magnets (SMMs) for over a decade. In comparison to their transition metal counterparts, the anisotropy of single lanthanide ions is large. The more recent and eye-catching advances in SMM synthesis have therefore involved lanthanide complexes having large anisotropic magnetic moments, and these studies have 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, the structure of the magnetic core, and the properties of the ligands. 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 intrinsic, ligand-free impact of cluster geometry and spin strain on the electronic and magnetic properties of SMM cores. Spectra exhibit the typical binding energies of lanthanide oxide clusters (between 0.7eV and 1.2eV) and photoelectron angular distribution anomalies we attribute to interactions between ejected photoelectrons and remnant neutral clusters are observed. Computational studies suggest a complex spectrum composed of numerous and close-lying energetically-accessible electronic states.

Small transition metal oxide clusters provide insight into the evolution of the properties from molecular to bulk level. Stoichiometric Zn_xO_x clusters in the small cluster size regime have been the topic of several computational studies and mass spectrometry studies, and electronic structures of species with x \textgreater 5. In the current study, the angle-resolved photoelectron spectra of stoichiometric Zn_xO_x⁻ clusters (2 ≤ x ≤ 5) are presented along with supporting DFT calculations. The spectra for all the Zn_xO_x⁻ clusters show features consistent with D_xh symmetric planar ring structures. The Zn₂O₂⁻ spectrum shows evidence of an additional, previously unpredicted bent chain structure for Zn₂O₂⁻, which is lower in energy than the D_2h structure on the anion surface, but higher in energy on the neutral surface. The DFT calculations also provide insights into how the singlet-triplet energy gap correlates to the cluster size, as well as the anomalous photoelectron angular distributions observed for several of the clusters.

The MP2 and CCSD(T) methods have been paired with correlation consistent basis sets as large as aug-cc-pVQZ to optimize the structures of the cyclic minima for (HF)_n, (HCl)_n and (H₂O)_n where n=3−5, as well as the corresponding transition states (TSs) for concerted proton transfer (CPT). MP2 and CCSD(T) harmonic vibrational frequencies have confirmed the nature of each minimum and TS. Both conventional and explicitly correlated CCSD(T) computations have been employed to assess the electronic dissociation energies and barrier heights for CPT near the complete basis (CBS) limit for all 9 clusters. At the CBS limit, MP2 significantly underestimates the CCSD(T) barrier heights (e.g., by ca. 2, 4 and 7 kcal mol⁻¹ for the pentamers of HF, H₂O and HCl, respectively), whereas CCSD overestimates these barriers by roughly the same magnitude. Scaling the barrier heights and dissociation energies by the number of fragments in the cluster reveals strong linear relationships between the two quantities and with the magnitudes of the imaginary vibrational frequency for the TSs. The extension of this work to the heterogeneous trimers, tetramers and pentamers composed of these 3 fragments (HF, HCl and H₂O) will also be discussed.

Considering the omnipresence of water, understanding the early stages of the interaction between water and complex organic molecules is of fundamental interest, and has been the subject of several spectroscopy studies. In particular, studying the micro-hydration of molecules with a degree of flexibility and various docking sites can provide invaluable insights into the interplay between the electrostatic and dispersive forces at play. It can also expand our understanding of binding motifs and conformational preferences for each water containing cluster which is the basis for molecular recognition processes. Here, we explore the first stages of the micro-hydration of 1-pyrrolepropionitrile (1-PPN), a N-containing heterocycle with a flexible propionitrile substituent. The spectra of 1-PPN…(wa)_n clusters, which were formed in a gaseous sample containing 1-PPN, water and neon, were recorded with Chirped pulse Fourier transform microwave (CP-FTMW) spectroscopy in the 2-8 GHz frequency region. Spectral analysis was aided by density functional theory (DFT) calculations, and unique molecular rotational parameters were generated for each cluster. Experiments with ¹⁸O-isotopically enriched water allowed for pinpointing the position of each water molecule within each cluster. The competing nature of attractive forces, due to inter- and intramolecular interactions, was broken down through symmetry adapted perturbation theory (SAPT) analysis.

Gas-phase metal clusters can act as idealized model systems for the active sites of more complex catalysts,Lang, S. M., Bernhardt, T. M. Phys. Chem. Chem. Phys., 14 9255 (2012)llowing for studies aimed at a fundamental understanding of metal-molecule interactions. In these experiments, we focus on understanding the adsorption of simple molecules on the model catalysts and establish the influence of local geometric and electronic structure as well as elemental composition. We do these investigations using a combination of mass-spectrometry, allowing studies of clusters with precise atomic and elemental composition, and free-electron laser-based IR spectroscopy. The experimental work is complemented by DFT calculations, allowing for structure determination and a rationalization of the formed products.Lushchikova, O. V. et al; J. Phys. Chem. Lett 10, 2151 (2019); Phys. Chem. Chem. Phys 2021, 23, 26661 (2021); J. Phys. Chem. A 125, 2836 (2021)Szalay, M. et al; Phys. Chem. Chem. Phys., 23, 21738 (2021) In this contribution, we present our results on the adsorption of CO₂ onto pristine cobalt clusters and how the substitution of a single cobalt atom by a vanadium atom leads to activation and dissociation. Lang, S. M., Bernhardt, T. M. Phys. Chem. Chem. Phys., 14 9255 (2012)a Lushchikova, O. V. et al; J. Phys. Chem. Lett 10, 2151 (2019); Phys. Chem. Chem. Phys 2021, 23, 26661 (2021); J. Phys. Chem. A 125, 2836 (2021)

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