Methanol clusters are a subject of great interest as they give insight into the nature of van der Waals complexes. In the course of our experimental study of the protonated formaldehyde ion, we have encountered unknown spectral lines that are believed to arise from methanol clusters. Both the methanol dimer and methanol-argon clusters have been previously observed experimentally. These studies have been limited to the microwave regime between 7 to 26 GHz. The observed spectra of both molecules are dense due to the splittings that occur because of the low barriers to internal motion. Here we present our findings, analysis of the unidentified lines that are present in our experimental results, and our progress to extend the spectra of methanol dimers and methanol-argon clusters from 50 to 1000 GHz.

In the last few years the development of chirp pulsed Fourier transform microwave (CP-FTMW) spectrometers has enables the studies of relatively large rotors and observations of molecular clusters that were difficult to detect previously. In this work we present the study of large oligomers of difluoromethane ((CH₂F₂)_n, with n from 5 to 7) for which experimental measurements were obtained during a collaboration between different research groups (especially at the University of Virginia – USABroadband Fourier transform rotational spectroscopy for structure determination: The water heptamer. C. Perez et al. Chem. Phys. Lett. 571 (2013) 1-15.nd Universidad del País Vasco – SpainStructural Studies of Nicotinoids: Cotinine versus Nicotine. I. Uriarte et al. Chem. Eur. J. 23 (2017) 7238 -7244.. State-of-the-art quantum chemical calculations and structural results for the molecular species will be presented. The challenging decomposition of the spectrum into the individual rotational spectra for each species presented in the jet expansion will be carried out. In particular the approach using AUTOFIT algorithmAUTOFIT, an automated fitting tool for broadband rotational spectra, and applications to 1-hexanal. N.A. Seifert et al. J. Mol. Spectrosc. 312 (2015) 13-21.unning on Amazon Web Service (AWS) and High Performance Computing (HPC) systems and its modified version for large molecular system will be presented.

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Broadband Fourier transform rotational spectroscopy for structure determination: The water heptamer. C. Perez et al. Chem. Phys. Lett. 571 (2013) 1-15.a Structural Studies of Nicotinoids: Cotinine versus Nicotine. I. Uriarte et al. Chem. Eur. J. 23 (2017) 7238 -7244.) AUTOFIT, an automated fitting tool for broadband rotational spectra, and applications to 1-hexanal. N.A. Seifert et al. J. Mol. Spectrosc. 312 (2015) 13-21.r

Over the past two years, we have implemented automated analysis of chirped-pulse microwave spectra of two-component mixtures of fluoroethylene (FE) or 1,1-difluoroethylene (DFE) and CO₂ to facilitate identification of the numerous cluster spectra present in a single scan.Rebecca A. Peebles, Prashansa B. Kannangara, Sean A. Peebles, Brooks H. Pate, 73rd International Symposium on Molecular Spectroscopy, Talk TH02, June 19, 2018.his approach has led to assignment of ten (FE)_n(CO₂)_m clusters and one (DFE)_n(CO₂)_m cluster, so far. These scans also include spectra of multiple single-component clusters (for instance, (FE)_n), which were not apparent in earlier analyses, since “monomer only” peaks were filtered from data sets during analysis. Present efforts utilize intensity variation amongst two-component scans as a way to identify these single-component clusters. Previously unobserved spectra for five clusters involving only FE or only DFE (and in some cases including neon) have now been assigned. Identifying groups of related transitions and assigning their spectra has proven relatively straightforward, but determining compositions and structures of the carriers of these spectra is challenging. Several approaches, including analysis of the concentration dependence of transition intensity and implementation of rapid force-field based structure optimizations, have allowed some progress on determining details of the observed species.

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Rebecca A. Peebles, Prashansa B. Kannangara, Sean A. Peebles, Brooks H. Pate, 73rd International Symposium on Molecular Spectroscopy, Talk TH02, June 19, 2018.T

Iron oxides have been used in a number of societally important catalytic processes; however, the molecular-level details behind their reaction mechanisms have been a challenge to observe. Molecular clusters have gained experimental attention due to their ability to model bulk materials, ease of production, and direct application for gaining atomic level insights. Using laser ablation combined with femtosecond pump-probe spectroscopy, the gas-phase dissociation and excitation-relaxation dynamics of neutral iron clusters in the presence of oxygen are observed. Dissociation/fragmentation time of neutral iron oxide clusters from (FeO)_n (n = 1-10) decreases with increased molecular size from > 300 fs to  ∼ 150 fs. Clusters deviating from the 1:1 stoichiometry are generally seen to increase in relaxation time, owing to an increased stability induced by a caging effect from atomic oxygen. A notable example of dissociation stability is observed with the addition of O atoms from Fe₂ → Fe₂O₂ which decreases in relaxation time from > 650 fs to < 250 fs. The molecular-level insights from these cluster studies provides a more comprehensive understanding for the design of future catalysts, leading to iron oxide materials with increased reactivity and decreased impact.

The structure of the microsolvated complexes of phenanthridine (PAN) with up to three water molecules has been investigated previously using chirped pulse Fourier transform microwave (CP-FTMW) spectroscopy from 2-8 GHz. In this work, the effect of Resonance Assisted Hydrogen Bonding (RAHB), also called π–cooperativity, on those complexes has been studied. In the resonant forms, the increase of the electronic density around the nitrogen nucleus enhances its hydrogen acceptor capabilities. Thus, the main effects expected due to the resonance of the multiple conjugated π–bonds in the structure of the complexes are a strengthening of the hydrogen bonds and a lengthening of the N-C bonds. However, due to the subtle changes that occur on the molecular structure, the effect on the N-C distances could not be detected experimentally and only a shortening of the hydrogen bonds has been observed. Therefore, the use of the quadrupole coupling interactions as a probe for the polarization has been used to investigate these effects on the almost planar structures of PAN-(H₂O)_n n=1-3. This form of analysis has been shown to be effective in similar studies with formamide.S. Blanco, P. Pinacho, J. C. López, Angew. Chem. Int. Ed., 2016, 128, 9477-9481.^,S. Blanco, P. Pinacho, J. C. López, J. Phys. Chem. Lett., 2017, 8, 6060−6066.he experimental quadrupole coupling constant χ_cc shows a clear trend from isolated PAN to complexes with higher hydration degree, illustrating how the electronic environment at the ^14 S. Blanco, P. Pinacho, J. C. López, J. Phys. Chem. Lett., 2017, 8, 6060-6066.T

To date, carbon-selenium clusters have received little attention from both experiment and quantum-chemistry. Recent high-resolution infrared survey scans of the ablation products from carbon-selenium targets in the 5μm regime have revealed two bands previously not observed in the gas phase. On the basis of comparison with high-level quantum-chemical calculations performed at the CCSD(T) level of theory these bands are attributed to the linear SeC₃Se and C₃Se chains. Following the microwave detection of diatomic CSe some 45 years agoJ. McGurk, H. L. Tigelaar, S. L. Rock, C. L. Norris, and W. H. Flygare, J. Chem. Phys. 58, 1420 (1973).he present work marks the first high-resolution detection of polycarbon selenium clusters.

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J. McGurk, H. L. Tigelaar, S. L. Rock, C. L. Norris, and W. H. Flygare, J. Chem. Phys. 58, 1420 (1973).t

Due to its large band gap and uniquely layered crystalline structure, MoO₃ is an attractive material in the field of organic photovoltaics. MoO₃ has also been reported to exhibit photo- and electrochromic activity, and shows great promise as a catalyst, sensing material, and electrode in lithium-ion batteries. Previous studies have explored the reactivity of the Mo_xO_y + H₂O → Mo_xO_y+1 + H₂ reaction. This most recent study introduced Mn to the Mo_xO_y structure in order to create a less oxophilic metal center. Photoelectron spectroscopy aided by a newly implemented planar ion funnel were utilized to probe the unique electronic properties of anionic MoMnO_y⁻ clusters reacted with H₂O, to illuminate how this substituted element impacted the two-centered mechanism of hydrogen evolution. Of particular interest were the structures of MoMnO₄⁻ when produced by direct laser ablation and as a product of oxidation of MnMoO₃⁻ with H₂O.

Density functional theory calculations were used to explore the structures of Cerium oxide and boride clusters CeO₂B₂⁻, CeO₂B₃⁻-, and CeB₆⁻. The results show intriguing structure and bonding trends, which are dependent on the ratio of boron centers to oxygens and the oxidation state of the cerium center. Natural ionization orbital analysis was also used to determine the nature electron detachment in photoelectron spectra of these species and to probe resulting electron rearrangement upon ionization. Such analysis allows us to differentiate between one-electron detachments and shake-up/shake-off transitions.