The vast majority of biological processes takes place in aqueous environments. The biomolecule’s biological function is therefore strongly influenced by its interactions with the solvating water molecules. Quantifying these interactions at a molecular level, when the organic molecule of interest is only surrounded by a few water molecules, serves as a valuable route to better understand the particular molecular behavior. In this talk, we will present our results on the stepwise hydration of Glycoaldehyde (Gly) from broadband rotational spectroscopy. Taking advantage of the high resolution and sensitivity of this technique, the experimental structures of (Gly)-(H₂O)_n (n=1-5) clusters have been determined and will be presented. An unambiguous identification of these clusters has been achieved from the spectra of the parent species and H₂¹⁸O single substitution of the water units within the clusters. These experiments allowed for an accurate determination of the oxygen-atom framework in the cluster. The experimental hydrogen bond networks will be discussed and compared to those of bare water clusters showing that certain topologies are recurrent.

We have studied water induced zwitterionization of glycine using helium nanodroplets isolation infrared spectroscopy. In the past, this process has been studied using matrix isolation infrared spectroscopy.¹ However, spectroscopic fingerprint for zwitterion formation could not be assigned, unambiguously. This triggered various theoretical studies for predicting the energetic stabilization and vibrational fingerprint of zwitterionic glycine-(H₂O)_n (n=1-10) clusters.² In this study, we have exploited the barrier free diffusion property of helium droplets to stepwise add water molecules to one molecule of glycine. Herein we present the infrared spectra of glycine-(H₂O)_n clusters recorded in the range of 1000-1850 cm⁻¹, using the free electron lasers (FELs) at FELIX laboratory in Nijmegen. References: 1) R. Ramaekers, J. Pajak, B. Lambie and G. Maes, J. Chem. Phys., 120, 4182 (2004). 2) R. Perez de Tudela and D. Marx, J. Phys. Chem. Lett., 7, 5137 (2016). Note: This work was supported by the Cluster of Excellence RESOLV (Ruhr-Universitat EXC1069) funded by the Deutsche Forschungsgemeinschaft, Stichting voor Fundamenteel Onderzoek der Materie (FOM) and LASERLAB-EUROPE grant 654148 for the support of the FELIX Laboratory.

Gas-phase hydrated clusters are treated as a microscopic model of hydration networks. Recently, we have revealed the temperature-dependence of hydration structures of hydrated phenol cation, [PhOH(H₂O)₅]⁺.H. Ishikawa, I. Kurusu, R. Yagi, R. Kato, Y. Kasahara, J. Phys. Chem. Lett. 8, 2641 (2017).n the cold condition (30 K), only an isomer having a ring-with-tail type hydration motif (Rt isomer) exists, whereas chain-like isomers (Ch isomer) are dominant in the hot condition (150 K). Isomerizations among the isomers having distinct hydration motifs can be related to structural fluctuations in the bulk systems. Thus, we have investigated the isomerization of the hydrated phenol cation trapped in the cold trap. In the last symposium, we reported the observation of the isomerization from the Rt to the Ch isomers. However, the quality of the spectra was not good enough. To improve the signal to noize ratio of the spectra, we introduced an octopole ion trap instead of the 22-pole ion trap, since an spatial overlap between the ions and the laser beam is expected to be better. In the present paper, we will report the progress of our study involving the time profile of the isomerization induced by the IR excitation. H. Ishikawa, I. Kurusu, R. Yagi, R. Kato, Y. Kasahara, J. Phys. Chem. Lett. 8, 2641 (2017).I

We have been carrying out spectroscopic studies on the Si-H…H-O type dihydrogen-bonded clusters. It was revealed that the strength of the Si-H…H-O type dihydrogen bond is comparable to that of the dispersion interaction and that the cluster structure is determined by the balance between these two interactions. To examine an effect of a change in the balance between them, we recorded the IR spectra of phenol-alkylsilane clusters in the S₁ state. In the course of our study, we found that the OH stretching band profile consists of several bands involving the excitation of the intermolecular vibrational modes. These band profiles are referred to as the Franck-Condon-like patterns. In the case of the phenol-t-butyldimethylsilane cluster, the band patterns simulated based on the Franck-Condon factors for the intermolecular vibrational mode have reproduced the observed patterns very well. This behavior indicates the interaction between the OH stretch and intermolecular vibrational modes. On the other hand, the infrared spectra of the electronic excited states of phenol-ethyldimethylsilane dihydrogen-bonded cluster indicate the contribution of two intermolecular vibrational modes. In this case, we analyzed the band pattern involving effects of the Duschinsky rotation as well as the displacements of the equilibrium positions for the v_OH = 0 and 1 states. In the present paper, we report the details of the analysis of the Franck-Condon-like patterns.

Cluster anions are commonly made in Smalley-type laser ablation sources, which generate a wide range of species in different charge states, potentially causing ion loss due to charge recombination in thermalization channels. We present an anion photoelectron spectroscopy study of anions selectively funneled into a thermalization channel using a planar ion funnel (PIF). This funnel can increase ion current and allow selection of different portions of the ion plume generated in the cluster source. The vibrational temperatures of funneled anions are evaluated by analysis of hot band transitions, and we present the advantages and disadvantages of implementing this mass spectrometric tool in studies that rely on ablation for ion production.

A time of flight mass spectrometry study for multi-photon ionization dissociation of monomers and dimers of 2- and 3-fluorophenols (2FP and 3FP) by a pulsed UV laser light of wavelength 266 nm will be presented. For these molecules, HF elimination from the excited and ionic states is a vital reaction channel. Our measurements reveal that the reaction does not occur from the monomer of 3FP, but it does occur with a measurable yield from the monomer cation of 2FP. On the other hand, upon formation of hydrogen bonded dimers, this reaction is triggered in the cation of 3FP, but for 2FP dimer cation the reaction is so facile that no intact dimer cation survives and only the HF eliminated dimer ion shows up in the mass spectrum. Electronic structure theory predicts that in the D₀ state of 2FP dimer cation, HF elimination is exothermic, but the process encounters a large barrier, 2.75 eV. However, in S₁ state of the dimer the reaction is predicted to be barrierless. Thus, we propose that for this dimer, HF elimination takes place in the intermediate S₁ state, and the remaining fragment that has relatively lower ionization energy is ionized effectively by an overall two-photon (1+1) process. For the reaction to occur from 3FP dimer cation, a rearrangement of the dimer geometry and formation of an intermediate adduct has been suggested, and it is argued that the latter could be produced by nucleophilic attack of the neutral moiety at the ortho site of the cationic counterpart, and the whole process requires 3-photon (2+1) absorption.

Changes of the excess charge accommodation motif in hemibonded hydrogen sulfide by microsolvation are studied by infrared spectroscopy of the [(H₂S)₂(X)₁]⁺ (X = water, methanol, and ethanol) clusters. While the hemibond in the (H₂S)₂⁺ ion core is stable to the microhydration by a single water molecule, it is broken by the proton transfer with the microsolvation by a single methanol or ethanol molecule. Hetero hemibond formation between hydrogen sulfide and these solvent molecules is not observed. On the other hand, the H₃S⁺ ion core in the protonated H⁺ (H₂S)₂ cluster is switched to H₃O⁺ ion core by the microhydration with a single water molecule, even though the proton affinity of water is lower than that of hydrogen sulfide.

Nanoscale engineering shows tremendous promise for developing new devices in energy transfer and storage, chemical synthesis, sensing, and a host of other applications. These applications critically depend on controlling electronic structure, but synthetic and experimental limitations hamper efforts to link electronic structure to dynamics and chemistry. We are overcoming these limitations by recording gas-phase, ultraviolet-visible (UV-Vis) spectra of ligand-protected gold nanoclusters with compositions precisely selected from a mixture by mass spectrometry. Clusters consisting of 6 to 9 gold atoms and varying ligand count and type were collected at 36 K and 4 K, with nitrogen and helium gas, respectively, physisorbing onto the surface of the clusters and acting as solvents. These spectra provide an unprecedented level of detail on the electronic structure of the clusters due to the homogeneous, contaminant-free environment and cryogenic temperatures in our instrument. With the aid of computational studies, experiments and analysis are underway to definitively assign the spectral features and to determine the factors that lead to shifts and splitting of transitions. The number and type of ligand and solvent species have a significant impact on transitions expected to involve only core metal atoms. Tracking the changes in the electronic transitions of gold nanoclusters with respect to chemical composition and structure will allow us to develop design rules to chemically manipulate their electronic structure, analogous to those developed for organic and organometallic molecular systems.