Monoterpenoids are chemical compounds derivatives of isoprene. They are naturally produced mainly by plants and vegetations. Many of them are involved in atmospheric chemistry since they represent about 11% of the global biogenic emission, while some of them have important biological activity. Cuminol (4-isopropylbenzyl alcohol, CA), a monocyclic monoterpenoid, was found to be the main compound in Rhodiola essential oil, having a specific spicy fragrance, which emphasizes the flower scent of rose root rhizomes. It may play a role in atmospheric chemistry since it is related to the abundant atmospheric monoterpene p-cymene. CA is an important biological compound since it has an analgesic effect,M.A. Sheikholeslami, S. Ghafghazi, S. Parvardeh, S. Koohsari, S.H. Aghajani, R. Pouriran, L.A. and Vaezi, 2021. European Journal of Pharmacology, 900, p.174075.nd it has been found in different medicinal plants. It is also a potent insulinotropic molecule that can enhance insulin secretion.S.B. Patil, S.S. Takalikar, M.M. Joglekar, V. S. Haldavnekar, and A.U. Arvindekar, British journal of nutrition, 2013, 110, 1434-1443.s biological activity is linked to the structure, it is important to characterize the conformational landscape in the gas phase. Using a combination of broadband rotational spectroscopy and theoretical calculations, one rotamer has been observed. Its identity has been confirmed by studying deuterated species enabling the determination of OH position and consequently been assigned to the lowest energy conformer. The interaction between CA and one water molecule has been also studied. Its spectrum showed tunneling effect. The splitting is associated with an internal dynamic of water inside the complex.

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M.A. Sheikholeslami, S. Ghafghazi, S. Parvardeh, S. Koohsari, S.H. Aghajani, R. Pouriran, L.A. and Vaezi, 2021. European Journal of Pharmacology, 900, p.174075.a S.B. Patil, S.S. Takalikar, M.M. Joglekar, V. S. Haldavnekar, and A.U. Arvindekar, British journal of nutrition, 2013, 110, 1434-1443.A

The benzene-methane complex is a prototypical model for CH/π interaction. The binding energyK. Shibasaki, A. Fujii, N. Mikami, and S. Tsuzuki, J. Phys. Chem. A 110, 4397-4404 (2006).nd UV spectraJ. A. Menapace and E. R. Bernstein, J. Phys. Chem. 91, 2533-2544 (1987).f this system have been reported and ab initio calculations were performedS. Tsuzuki, Annu. Rep. Prog. Chem., Sect. C: Phys. Chem., 108, 69-95 (2012). However, full dimensional (6D) intermolecular potential energy surface (IPS) has not been evaluated because of difficulties caused by high dimensionality. In order to reconstruct a full dimensional IPS in the benzene-methane system, stimulated emission pumping and wave-packet observation pertinent to the S₀ state were carried out. The latter was performed as a pump-probe experiment combining impulsive stimulated Raman excitation by femtosecond pulses with state-selective ionization by resonant two-photon ionization. A new 6D model potential analysis was also performed. Single-point energy calculations were performed at CCSD(T)/aug-cc-pVTZ level of theory for 525 different complex configurations, and calculated results were fitted by the new model potential. Observed intermolecular bands were assigned by comparing the theoretical prediction. Deviations of the prediction from the observation are well within 3 cm⁻¹, which verifies the utility of the present IPS for benzene-methane.

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K. Shibasaki, A. Fujii, N. Mikami, and S. Tsuzuki, J. Phys. Chem. A 110, 4397-4404 (2006).a J. A. Menapace and E. R. Bernstein, J. Phys. Chem. 91, 2533-2544 (1987).o S. Tsuzuki, Annu. Rep. Prog. Chem., Sect. C: Phys. Chem., 108, 69-95 (2012)..

The size of the attainable target systems for broadband rotational spectroscopy has been steadily increasing since its introduction in 2006. In 2013, we presented at this conference the characterization of the sevoflurane dimer. This complex represented, at that time, one of the larger systems observed through rotational spectroscopy. The collected spectrum exhibited a large dynamic range and many transitions remained unassigned. With the advent of newer, faster and more reliable conformation sampling tools like CREST and automated fitting routines such autofit and its implementation in Pgopher, we reassessed the ability of rotational spectroscopy to probe increasingly larger, heavier systems. In this talk we will present the observation of the sevoflurane trimer by chirped-pulse Fourier transform microwave spectroscopy, identified through the interplay of experimental and computational methods. The trimer ( > 600 Da), one of the largest molecular aggregates observed through rotational spectroscopy, showcases the potential of rotational spectroscopy to study larger biochemical systems but also uncovers the challenges ahead as the mass of the system increases. These will be presented and discussed.

Based on a preliminary investigation into the rotational transitions of the van der Waals complex O₂-H₂O using a chirp pulse FTMW spectrometer, the 2-6GHz region of the electromagnetic spectrum was explored for rotational transitions using a cavity FTMW instrument. Focus of the study was around the 5 GHz region as the preliminary chirp pulse FTMW spectra, theoretical calculations, and previous workKasai, Y., Dupuy, E., Saito, R., Hashimoto, K., Sabu, A., Kondo, S., Sumiyosihi, Y., & Endo, Y. (2011). The H₂O-O₂ water vapour complex in the Earth's atmosphere. Atmospheric Chemistry and Physics, 11(16), 8607-8612. https://doi.org/10.5194/acp-11-8607-2011mply transitions are present in this region but have yet been reported. The collected spectra will be presented and discussed along with new working fits taking these rotational transition assignments into account.

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Kasai, Y., Dupuy, E., Saito, R., Hashimoto, K., Sabu, A., Kondo, S., Sumiyosihi, Y., & Endo, Y. (2011). The H₂O-O₂ water vapour complex in the Earth's atmosphere. Atmospheric Chemistry and Physics, 11(16), 8607-8612. https://doi.org/10.5194/acp-11-8607-2011i

Microwave spectroscopy is a powerful technique for the study of weakly bound complexes formed between aromatic/heteroaromatic rings and other small molecules. However, there has been limited studies of binary complexes formed between alkyl-substituted heteroaromatic rings and water. The rotational spectrum of 2-ethylfuran···H₂O was recorded while probing a gaseous mixture of 2-ethylfuran, water and an inert carrier gas (argon or neon) using Chirped Pulse Fourier Transform Microwave (CP-FTMW) spectroscopy. Microwave spectra of five isotopologues of this complex have been assigned and analysed to determine rotational constants (A₀, B₀, C₀) and centrifugal distortion constants (D_J, D_JK, d₁). A previous microwave spectroscopy studyH. V. L. Nguyen, Journal of Molecular Structure, 2020, 1208, 127909.dentified two conformations (C_s and C₁) of 2-ethylfuran in a helium supersonic expansion. The C_s conformation is planar, with the ethyl group lying coplanar with the ring, while the ethyl group in the C₁ conformation is tilted out of the plane of the ring. The analysis of the molecular geometry of the monohydrate complex has revealed that the binary complex is formed with the C₁ conformation of 2-ethylfuran only and is stabilised by a primary O_W-H···O hydrogen bond. Additionally, non-covalent interaction (NCI) and natural bond orbital (NBO) analysis have revealed the presence of additional weak interactions between the oxygen atom of the water molecule and the ethyl group. Preliminary results of 2-ethylimidazole···H₂O and 2-ethylthiazole···H₂O will also be discussed. H. V. L. Nguyen, Journal of Molecular Structure, 2020, 1208, 127909.i

The chiral-tagging method based on rotational spectroscopy is gaining relevance for investigating chirality in the gas phase B. H. Pate, L. Evangelisti, W. Caminati, Y. Xu, J. Thomas, D. Patterson, C. Pérez and M. Schnell, Chiral Analysis, Elsevier, 2nd edn, 2018, pp. 679–729.^, Sergio R. Domingos, Cristóbal Pérez, Mark D. Marshall Helen O. Leung b and Melanie Schnell, Chem. Sci., 2020, 11, 10863E

l0pt Figure The looming threat of anthropogenic climate change has driven a significant amount of research into efficient methods of capturing and storing^[1] CO₂. Reversible capture mechanisms, such as those governed by weakly bound intermolecular interactions, have been a mainstay of such research. To this end, the rotational spectrum of the pyrimidine (C₄H₄N₂)-CO₂ van der Waal’s complex has been measured using broadband chirped-pulse Fourier transform microwave (CP-FTMW) spectroscopy across a frequency range of 7.5 to 17.5 GHz, in an effort to investigate the viability of pyrimidine as an active site in CO₂ capture media. A preliminary fit of the spectrum indicates a structure whereby the lone pair of one of the nitrogen atoms is directed towards the CO₂ carbon atom, with the O=C=O axis lying in the plane of the pyrimidine moiety and approximately perpendicular to a line drawn through the corresponding nitrogen atom and the pyrimidine centre-of-mass. This is analogous to the structure of the pyridine-CO₂ complex^[2], and in agreement with the structures predicted by DFT calculations performed at a wB97XD/6-311++G** level of theory, as well as previously published computational studies^[3]. The principal rotational constants produced by this fit are: A = 4070.9905(46) MHz, B = 859.4088(12) MHz and C = 710.01942(85) MHz.

^[1]C. Yu, et. al., Aerosol Air Qual. Res. 2012, 12, 745-769
^[2]J. L. Doran., et. al., J. Mol. Struct. 2012, 1019, 191-195
^[3]K. D. Vogiatzis, et. al., ChemPhysChem 2009, 10, 374-383

Carbohydrates are the main source of energy and make up the main backbone of DNA and RNA, which make them, among many biological systems, of particular interest. Furthermore, they take part in the recognition process, where has been demonstrated that water is actively involved. The role that water molecules play in glycobiology is crucial and is not yet well understood, in part, for the lack of experimental information about how water comes into play in the monosaccharide conformations. Here we present xylopyranose-water complex, first microhydrated monosaccharide studied in gas phase using the combination of laser ablation and broadband microwave spectroscopy. The revealed way in which water binds to the xylopyranose molecule, among the many possibilities due to the high capacity to form hydrogen bonds, can be considered the first step in understanding the mutarotation processes that monosaccharides undergo in biological environments.

We report on the hydration of the superacid fluorosulfonic acid (FSO₂OH) as characterized by chirped-pulse and cavity microwave spectroscopy. Rotational transitions of the monomer in the 3-18 GHz region were readily observed. Each has a weaker partner arising from OH wagging, as previously observed in the spectra of triflic and methanesulfonic acids. Spectra for the monohydrate and dihydrate were collected using a chirped-pulse method, and rapidly assigned using the DAPPERS software. Cavity spectroscopy revealed two states for the monohydrate, presumably arising from an internal motion associated with the water moiety. Deuterium isotopologues of these complexes were collected by on-the-fly mixing using D₂O in place of H₂O. The computed structures (benchmarked against the observed rotational constants), involve hydrogen bonded rings analogous to those observed for many other hydrated oxyacids. Consistent with previously published theoretical workLi, S.; Weber, K.H.; Tao, F.-M.; Gu, R. Theoretical Investigation of Ionic Dissociations of Fluorosulfonic Acid in Microsolvated Clusters, Chem. Phys. 2006, 323, 397-406. acid dissociation is not predicted or observed for the mono- or dihydrates, although a correlation between degree of partial proton transfer and hydration is noted. The trihydrate is predicted to exist as a hydrated ion pair, but no such species has yet been identified in the observed spectrum.

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Li, S.; Weber, K.H.; Tao, F.-M.; Gu, R. Theoretical Investigation of Ionic Dissociations of Fluorosulfonic Acid in Microsolvated Clusters, Chem. Phys. 2006, 323, 397-406.,

Non-covalent interactions play a key role in the formation of molecular complexes and reactivity. In previous works only interactions of small molecules with hydrogen have been investigated by rotational spectroscopy while interactions of molecular hydrogen with aromatic systems are unexplored. In this work, the bond of hydrogen to the π-system of halogenated benzaldehydes is investigated. These volatile systems possess a large dipole moment and have multiple non-covalent binding sites to investigate selectivity. By introducing quadrupolar nuclei the complexity of the system is increased, the quadrupolar nucleus acts as a spectroscopic probe for the electronic field gradient and provides insights into the long-range dispersive interactions. Of particular interest are the differences observed for the rotational spectrum of ortho- and para-hydrogen and its structural impact investigated by isotopic substitution. The two spin isotopes show significant differences in rotational constants which demonstrate that there are significant differences in binding strength of o-H₂ and p-H₂ to the π-system, which are experimentally observable. Broadband rotational spectra are presented which are supplemented with cavity data to resolve the additional hyperfine splitting caused by the spin-spin coupling of o-H₂. We present elements of the spin-spin coupling tensor and draw experimental conclusions about hydrogen bond distance and the orientation of the o-H₂ with respect to the benzaldehyde plane.