Verbenone (C₁₀H₁₄O) is a bicyclic ketone terpene. It is one of the products of oxidation of α-pinene in the troposphere. It may have a significant role in the formation of secondary organic aerosols, in particular through its ability to interact with water molecules.Verbenone is almost insoluble in water so it is therefore important to understand how this type of molecules interacts with water. The rotational spectrum of verbenone and the determination of its r_s and r₀ molecular structures were recently investigated F. E. Marshall, G. Sedo, C. West, B. H. Pate, S. M. Allpress, C. J. Evans, P. D. Godfrey, D. McNaughton and G. S. Grubbs, J. Mol. Spectrosc. 342, 109 - 115 (2017). This work deals with the study of its hydrates. Water is expected to form a primary hydrogen bond with the carbonyl group of verbenone, and the hydrogen atoms of the -CH₃ or -CH₂ groups may form weak interactions with the lone pairs of the water oxygen to stabilize different hydrates. The structures of two monohydrates, two dihydrates and four trihydrates of verbenone were optimized at the DFT B3LYP-D3BJ / def2-TZVP and ab initio MP2 / 6-311++G(d,p) levels, before searching for their rotational signatures, using a supersonic expansion coupled to a cavity-based Fourier transform microwave spectrometer working in the 2 - 20 GHz frequency range. We were able to analyse the spectra of the expected two mono- and two dihydrates, and of the lowest energy conformer of the trihydrate. We also analysed the spectra of the water-¹⁸O substituted species using ¹⁸O labeled water. For each hydrate, the sets of rotational constants were used to calculate the substitution coordinates of the water oxygen atoms and an effective r₀ structure of the water arrangements of water around the molecule of verbenone. The present work was funded by the French ANR Labex CaPPA through the PIA (contract ANR-11-LABX-0005-01), by the Regional Council Hauts de France, by the European Funds for Regional Economic Development, and by the French Ministère de l'Enseignement Supérieur et de la Recherche. It is a contribution to the CPER research Project CLIMIBIO.

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F. E. Marshall, G. Sedo, C. West, B. H. Pate, S. M. Allpress, C. J. Evans, P. D. Godfrey, D. McNaughton and G. S. Grubbs, J. Mol. Spectrosc. 342, 109 - 115 (2017)..

The rotational spectra of ethyl carbamate-(H₂O)_n (n = 1, 2, 3) generated in a supersonic expansion have been studied using both a chirped-pulse and a molecular beam Fourier transform microwave spectrometer. Ethyl carbamate presents in the gas phase an equilibrium between two structures close in energy with a low interconversion barrier.K.-M. Marstokk, H. Møllendal, Acta Chem. Scand., 1999, 53, 329-334.^,M. Goubet, R. A. Motiyenko, F. Real, L. Margulés, T. R. Huet, P. Asselin, P. Soulard, A. Krasnicki, Z. Kisiel, E. A. Alekseev, Phys. Chem. Chem. Phys., 2009, 11, 1719−1728.he observation of these structures and their complexes strongly depends on the carrier gas used due to collisional relaxation in the supersonic jet. Using argon, only the most stable form and its water complexes are observed. Using neon, both forms and their corresponding complexes are observed. The structures of the complexes have been characterized and show water closing sequential cycles with the H−N−C=O amide group. They show structural and dynamical features similar to those observed, for example, in formamide−(H_2O)_n M. Goubet, R. A. Motiyenko, F. Real, L. Margulés, T. R. Huet, P. Asselin, P. Soulard, A. Krasnicki, Z. Kisiel, E. A. Alekseev, Phys. Chem. Chem. Phys., 2009, 11, 1719-1728.T

Supercritical carbon dioxide (sc-CO₂) is an increasingly common green solvent, so it is important that its physical properties are well understood. In the present study, chirped-pulse Fourier-transform microwave (CP-FTMW) spectroscopy was used to study weak hydrogen bonding interactions in complexes of fluoroethylene (FE) with CO₂. Previous investigations of 1:1 dimers of CO₂ with FE observed two isomers for FE...CO₂. Our current focus is analysis of weakly bound trimers, and FE…CO₂…CO₂ was recently observed in the 2 - 8 GHz range using the CP-FTMW spectrometer at the University of Virginia. Four structures were optimized at the MP2/6-311++G(2d,2p) level. As with FE…CO₂ dimer, spectra of two trimer isomers were observed experimentally, corresponding to the two lowest energy ab initio structures, which lie within 25 cm⁻¹ of each other. Although only planar forms of the isolated FE...CO₂ dimer were observed experimentally, both trimer structures trap a nonplanar dimer fragment, with one CO₂ molecule located above the plane of FE. Current work involves analysis of isotopic data to allow detailed structural comparisons, as well as searching for larger CO₂ clusters to explore structural changes as the number of solvating CO₂ molecules increases. Extended cross correlation and other techniques are being applied to assist assignment of the thousands of lines remaining in the scan and to suggest the carrier of a recently identified spectrum in the FE/CO₂ mixture.

Present in a wide spectrum of chemical systems, π-π stacking and hydrogen bonding are intermolecular forces critical to the formation and stabilization of various chemical structures. However, these forces can be found to be competitive interactions in stabilizing model systems. This competition is clearly exhibited in the dimer of phenol, where hydrogen bonding is preferred over π-π stacking.Seifert, N. A.; Steber, A. L.; Neill, J. L.; Pérez, C.; Zaleski, D. P.; Pate, B. H.; Lesarri, A. Phys. Chem. Chem. Phys. 2013, 15, 11468–11477.owever, it is unclear how this competitive relationship will evolve as a function of molecular shape. To explore this, we use 1-naphthol, a naphthalene analogue of phenol, as a model to further understand the complex interplay between π-π stacking and hydrogen bonding. Using chirped-pulse Fourier transform microwave (CP-FTMW) spectroscopy in the 2-6 GHz bandPérez, C.; Lobsiger, S.; Seifert, N. A.; Zaleski, D. P.; Temelso, B.; Shields, G. C.; Kisiel, Z.; Pate, B. H. Chem. Phys. Lett. 2013, 571, 1–15. we observed a spectrum that is size-consistent with a dimer of 1-naphthol, in addition to the pure rotational spectra of two conformers of 1-naphthol as well as weakly-bound 1-naphthol complexes with neon and H₂O. We present an experimental analysis supplemented with a structure search enabled by dispersion corrected DFT and corroborated by interaction energies at the CCSD(T) level of theory, that provides the identity of a likely molecular carrier for the observed dimer spectrum. This analysis suggests that the dimer structure of 1-naphthol is not at all like that of the phenol dimer; conversely, the spectrum is consistent with a structure that stabilizes nearly exclusively through a π-π stacking interaction. This is in contradiction to previous observations using IR dip spectroscopySaeki, M.; Ishiuchi, S.; Sakai, M.; Fujii, M. J. Phys. Chem. A 2007, 111, 1001–1005. which assigns the dimer vibrational spectrum to a hydrogen bonded structure.

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Footnotes:

Seifert, N. A.; Steber, A. L.; Neill, J. L.; Pérez, C.; Zaleski, D. P.; Pate, B. H.; Lesarri, A. Phys. Chem. Chem. Phys. 2013, 15, 11468–11477.H Pérez, C.; Lobsiger, S.; Seifert, N. A.; Zaleski, D. P.; Temelso, B.; Shields, G. C.; Kisiel, Z.; Pate, B. H. Chem. Phys. Lett. 2013, 571, 1–15., Saeki, M.; Ishiuchi, S.; Sakai, M.; Fujii, M. J. Phys. Chem. A 2007, 111, 1001–1005.,

15-crown-5 ether (15C5) and its complexes with water generated in a supersonic jet have been studied using broadband Fourier transform microwave spectroscopy. The most stable form of the crown ether not previously reported, to complete a total of nine isolated forms, has been detected. In addition, two 1:1 and two 1:2 clusters have been observed. The clusters structures have been unambiguously identified through the observation of water ¹⁸O isotopologue spectra and a detailed analysis of the rotational parameters. The structures of all the clusters show that at least one water molecule, located close to the axis of the ring, interacts through two simultaneous hydrogen bonds to the endocyclic oxygen atoms. This interaction reshapes the 15C5 ring to reduce its rich conformational panorama to only two open structures, related to those found in complexes with Li⁺ or Na⁺ ions. In the most intense 1:2 form, the two water molecules repeat the same interaction scheme in both sides of the ring while in the second one the water molecules lie on the same side of the ring.

The rotational spectrum for the complex formed between sulfur trioxide and sulfur dioxide has been observed by chirped-pulse and cavity Fourier transform microwave spectroscopy. Spectra were recorded for five isotopologues that include single substitution of ³⁴S and ³³S on each sulfur atom. Nuclear hyperfine structure was resolved for both ³³S isotopologues and their corresponding quadrupole coupling constants were obtained. Ab initio calculations predict a pair of structures which differ in energy by only 0.1 kcal/mol. In both structures, one oxygen of the SO₂ approaches the sulfur of the SO₃, but the two forms differ in the angular orientation of the SO₂. Despite the small calculated energy difference, only one set of spectra was identified. Isotopic substitution on SO₃ does not clearly distinguish between the two structures, but the experimental isotopic shifts and quadrupole coupling constants obtained for the SO₂ substituted isotopologues are more clearly consistent with those predicted for the lower energy form.

The rotational spectra of formamide and water mixtures have been recorded in the 2-8 GHz frequency region using a chirped-pulse Fourier transform microwave spectrometer. Samples of ¹⁴N and ¹⁵N of formamide have been used in this work. The ¹⁴N quadrupole coupling hyperfine structure is a tool to identify the structure of the observed complexes; the ¹⁵N isotopologue is of great help to explore the conformational panorama of complexes with several formamide units. In this work we present the detection and characterization of complexes of formamide and formamide-water, as F₃ and F-(H₂O)₄, which show interesting structural features.

As polycyclic aromatic hydrocarbons (PAHs) are of interest to many communities, including astronomers, it is important to understand the interactions that they may be a part of. As water is ubiquitous in astronomical environments and PAHs are thought to form ice grains, the PAH-water interactions are of specific interest. In this investigation we used chirped pulse Fourier transform microwave (CP-FTMW) spectroscopy from 2-8 GHz to study the fluorene monomer and its complexes with water. While the monomer has previously been studied [1], our use of the COMPACT [2] instrument allowed us to observe not only new transitions for the monomer but also transitions for ¹³C species. This allowed for a structural analysis of the monomer to be presented. This structural information is important when we move to complexes of PAHs with compounds such as water. We have previously studied the interactions of up to four water molecules clustered with the PAH acenaphthene (Ace)[3]. As in the Ace-water study, we have observed up to three water molecules complexed with fluorene and obtained isotopic data for the complexes. In this talk we will present these findings and the structural differences between the two PAH-water systems.
[1] Thorwirth, S., Theulé, P., Gottlieb, C.A., McCarthy, M.C., Thaddeus, P. Astrophys. J., 662, 1309-1314, 2007. [2] Schmitz, D., Shubert, V.A., Betz, T., Schnell, M. J. Mol. Spectro., 280, 77-84, 2012. [3] Steber, A.L., Pérez, C., Temelso, B., Shields, G.C., Rijs, A.M., Pate, B.H., Kisiel, Z., Schnell, M. J. Phys. Chem. Lett., 8, 5744–5750, 2017.

The 2-methoxybenzoic acid (o-anisic acid) and its complexes with water have been studied in the 2-12 GHz frequency region combining chirped-pulse Fourier transform microwave spectroscopy (CP-FTMW) and molecular Fourier transform microwave spectroscopy (MB-FTMW). o-Anisic acid has been vaporized using a heating nozzle were it partially reacts through a recombination reactions to give a series of products which have been all identified from its microwave spectra. Apart from these species, three different conformations for o-anisic acid, with distinct dispositions of carboxylic group, and two for the 1:1 water complex have been observed. For the lowest energy conformer of the monomer and the most abundant water complex, the spectra of various isotopologues have been measured and the molecular structures have been determined. Relative intensity measurements have been done to provide a better understanding of the complex formation in the supersonic expansion.

2-Methoxyethylamine (2MEA) exists in trans and gauche conformations, each with at least one intramolecular hydrogen bond from the amine to the methoxy oxygen. Rotational spectra of 2MEA, recorded by Caminati et al., exhibit splittings arising from methyl internal rotation tunneling (V₃ = 822.6 cm⁻¹ and 1102cm⁻¹ respectively).W. Caminati and E. B. Wislon, J. Mol. Spectrosc. 81, 356-372 (1980).^, W. Caminati, J. Mol. Spectrosc. 121, 61−68 (1987).We report the rotational spectra of the three ^13 W.Caminati, J.Mol.Spectrosc.121, 61-68 (1987).H.Hartwig and H.Dreizler, Z.Naturforsch, A:Phys. Sci.51, 923-932 (1996).A