Millimeter-wave spectra of acetyl chloride (CH₃COCl) and acetyl bromide (CH₃COBr) were measured in the frequency range 50-330 GHz. From a spectroscopic point of view, these molecules are interesting cases for studying methyl top internal rotation with relatively strong nuclear quadrupole coupling. Due to nonzero quadrupole moment of Cl and Br, the quadrupole hyperfine splittings in CH₃COCl and CH₃COBr molecules are comparable with splittings due to internal rotation. To fit the observed rotational transitions we used the so-called Rho-Axis-Method and RAM36hf codeV.V. Ilyushin, J. Mol. Spec. 345, 64-69 (2018)hat take nuclear quadrupole hyperfine structure into account. The analysis, which is in progress, includes the ground vibrational state as well as lowest excited torsional states. The latest results will be presented.

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V.V. Ilyushin, J. Mol. Spec. 345, 64-69 (2018)t

The high-resolution rotational spectrum of chlorosulfonic acid (ClSO₂OH) was studied using both broadband chirped pulse and cavity-based Fourier transform microwave spectrometers over the frequency range of 5–18 GHz for the first time. The observation of a-, b-, and c-type transitions for both ³⁵Cl and ³⁷Cl isotopomers suggests that the molecule exhibits large amplitude motion of the hydroxyl hydrogen flipping between two equivalent structures. The rotational constants, the centrifugal distortion constants, and the nuclear quadrupole coupling constants for the chlorine nucleus have been determined. The quantum chemical calculations were carried out using MP2 and B3LYP density functional theory (DFT) with aug-cc-pVTZ basis set. The rotational constants from the optimized geometric structures were in good agreement with the experimental values. The energy barrier of the large amplitude motion was calculated to be 12 kJ/mol. The effect of the large amplitude motion will be compared to the recent rotational spectroscopic study on triflic acid.Anna K.Huff, Nathan Love, C. J. Smith Kenneth R. Leopold; Parent, 34S, and deuterated triflic acid: Microwave spectra and tunneling splittings due to hydroxyl torsion, J. Mol. Spectrosc., 2022, 385, 111623.html:<hr /><h3>Footnotes: Anna K.Huff, Nathan Love, C. J. Smith Kenneth R. Leopold; Parent, 34S, and deuterated triflic acid: Microwave spectra and tunneling splittings due to hydroxyl torsion, J. Mol. Spectrosc., 2022, 385, 111623.

Dimethylfluorobenzene isomers (DMFB) are aromatic heterocyclic volatile organic compounds (VOCs). These VOCs are methylated toluene derivatives, one of the most prevalent aromatic hydrocarbons in the troposphere and considered as atmospheric pollutants. The spectrum of 2,4-dimethylfluorobenzene (24DMFB) has been recorded between 2.0 and 26.5 GHz using the LISA molecular jet Fourier transform microwave spectrometer with an estimated measurement accuracy of 4 kHz. Due to the internal rotation of two inequivalent methyl groups, all rotational transitions split into quintets. The spectral analysis was challenging due to the fact that one of the two methyl groups in 24DMFB have a torsional barrier of about 1 cm⁻¹, leading to large splittings between the torsional species. Using the SFLAMSS. Herbers, S.M. Fritz, P. Mishra, H.V.L. Nguyen, T.S. Zwier, J. Chem. Phys. 152, 074301, 2020.rogram, the assignments were checked by fitting separately each of the five torsional species. A global fit of 813 torsional lines was performed using the programs XIAMH. Hartwig, H. Dreizler, Z. Naturforsch. 51a, 923, 1996. ntopL. Ferres, W. Stahl, H. V. L. Nguyen, J. Chem. Phys. 151, 104310, 2019.nd BELGI-Cs-2TopsM. Tudorie, I. Kleiner, J. T. Hougen, S. Melandri, L. W. Sutikdja, W. Stahl, J. Mol. Spectrosc. 269, 211, 2011.iving standard deviations of 578.4 kHz, 13.3 and 4.7 kHz, respectively. The torsional barriers of the methyl groups in the ortho and para positions were determined to be 226.2087(16) and 1.4387(58) cm⁻¹, respectively.This work has been funded by the Programme National de Physique Chimie du Milieu Interstellaire (PCMI).html:<hr /><h3>Footnotes: S. Herbers, S.M. Fritz, P. Mishra, H.V.L. Nguyen, T.S. Zwier, J. Chem. Phys. 152, 074301, 2020.p H. Hartwig, H. Dreizler, Z. Naturforsch. 51a, 923, 1996., L. Ferres, W. Stahl, H. V. L. Nguyen, J. Chem. Phys. 151, 104310, 2019.a M. Tudorie, I. Kleiner, J. T. Hougen, S. Melandri, L. W. Sutikdja, W. Stahl, J. Mol. Spectrosc. 269, 211, 2011.g This work has been funded by the Programme National de Physique Chimie du Milieu Interstellaire (PCMI).

Phenylacetylene (PhAc) is a multifunctional molecule and has been termed a “Hydrogen Bonding Chameleon”Maity, S., Guin, M., Singh, P. C., & Patwari, G. N. (2011). ChemPhysChem, 12(1), 26-46. In 2008, Patwari and co-workers studied complexes of PhAc with various molecules, including H₂O and CH₃OH, by the IR-UV double resonance spectroscopic techniqueSingh, P. C., & Patwari, G. N. (2008). The Journal of Physical Chemistry A, 112(23), 5121-5125 This study found that H₂O donates the H-bond to the acetylenic π-system, whereas CH₃OH donates the H-bond to the phenyl π-system. Recently, Suhm’s group used FTIR spectroscopy of supersonic jet expansions to study PhAc with H₂O and CH₃OH and observed that both H₂O and CH₃OH donate H-bond to the acetylenic π-systemKarir, G., Lüttschwager, N. O., & Suhm, M. A. (2019). Physical Chemistry Chemical Physics, 21(15), 7831-7840 The acetylenic preference in the PhAc···H₂O complex has already been confirmed by rotational spectroscopydGoswami, M., & Arunan, E. (2011). Physical Chemistry Chemical Physics, 13(31), 14153-14162 In this work, the rotational spectrum of PhAc···CH₃OH complex has been studied. The rotational spectrum of the parent and isotopologues of PhAc···CH₃OH complex was recorded over the 2-8 GHz frequency range using the Chirped Pulse Fourier Transform Microwave (CP-FTMW) Spectrometer at Newcastle University, UK, and from 8-14 GHz using the Pulsed Nozzle Fourier Transform Microwave Spectrometer (PN-FTMW) at IISc Bangalore, India. The structure where CH₃OH donates the H-bond to the acetylenic π-system and CH₃OH accepts a weak H-bond through the ortho hydrogen of the PhAc was observed. The rotational transitions were split, indicating the internal motion of the CH₃ group in CH₃OH. The observed global minimum structure has been compared with several CH₃OH-containing complexes to understand the internal rotation of the CH₃ group and its effect on V₃ barrier height.

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Maity, S., Guin, M., Singh, P. C., & Patwari, G. N. (2011). ChemPhysChem, 12(1), 26-46.. Singh, P. C., & Patwari, G. N. (2008). The Journal of Physical Chemistry A, 112(23), 5121-5125. Karir, G., Lüttschwager, N. O., & Suhm, M. A. (2019). Physical Chemistry Chemical Physics, 21(15), 7831-7840. dGoswami, M., & Arunan, E. (2011). Physical Chemistry Chemical Physics, 13(31), 14153-14162.

The far infrared spectrum of propene, CH₃−CH=CH₂, has been measured at 193.65 K with a resolution of 0.00096 cm⁻¹on the FIR beamline at the Canadian Light Source (CLS) synchrotron. The torsional fundamental band ν₂₁ at 188 cm⁻¹is quite complex because the coupling of the angular momenta of the overall rotation with the internal rotation of the CH₃ group splits every rovibrational energy level (without internal rotation) into an A- and an E-component. As a result, every rovibrational transition splits into two or three components. To predict and assign the spectrum and to determine spectroscopic constants by the LS method, the ERHAM program P. Groner, J. Chem Phys. (1997) 107, 4483; J. Mol. Spectrosc. (2012) 278, 52as been modified to use it for rovibrational spectra. Initially, the spectroscopic constants for the ground state (GS) were fixed at the values determined by Craig et al.N. C. Craig et al., J. Mol. Spectrosc. (2016) 328, 1rom almost 900 microwave and millimeter-wave frequencies. This was good enough to begin the assignment of transitions of ν₂₁ involving low K_a levels. However, for K_a > 3, the ratio of the standard deviation over the estimated experimental uncertainty increased with increasing K_a despite the introduction of additional tunneling parameters. Only the inclusion of the internal rotation parameters ρ and β (which had been held constant with the GS constants) among the variable parameters brought the standard deviation down to an acceptable level. From then on, the transitions of ν₂₁ were used simultaneously with all GS transitions (footnote b) to fit the parameters of two different effective internal rotation Hamiltonians (one each for the GS and ν₂₁ levels) but with shared ρ and β. More than 6000 individual transitions (J up to 50, K_a up to 8) have been assigned so far for the ν₂₁ band and preliminary constants have been obtained, among them an improved internal rotation barrier.

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P. Groner, J. Chem Phys. (1997) 107, 4483; J. Mol. Spectrosc. (2012) 278, 52h N. C. Craig et al., J. Mol. Spectrosc. (2016) 328, 1f

The (V₃) barriers to internal rotation of many five-membered heteroaromatic rings have been investigated using microwave spectroscopy. The rotational spectra of 2-methylthiazole···H₂O, 4-methylthiazole···H₂O and 5-methylthiazole···H₂O were recorded over the frequency range 7.0-18.5 GHz using Chirped Pulse Fourier Transform Microwave (CP-FTMW) spectroscopy. The complexes were generated in a supersonic expansion containing low concentrations of a methylthiazole isomer and water in an argon buffer gas. In total spectra of five isotopologues of each complex have been assigned and analysed. The fitting of observed A-species transition frequencies to Watson’s S-reduced Hamiltonian within PGOPHER gave “effective” fits of each complex. Global fits (simultaneous fitting of both A- and E- species transitions) have been performed using XIAM allowing the determination of rotational constants (A₀, B₀, C₀), centrifugal distortion constants (D_J, D_JK, d₁, d₂) and nuclear quadrupole coupling constants (χ_aa(N) and χ_bb(N) - χ_cc(N)) as well as the V₃ barrier to internal rotation. The monohydrate complexes are formed by a non-linear hydrogen bond between H₂O acting as the hydrogen bond donor and the nitrogen atom of the methylthiazole ring which is the hydrogen bond acceptor. The influence formation of the monohydrate complex on the V₃ barrier will be discussed.

Isopropyl alcohol (CH₃−CHOH−CH₃) is a non-rigid species of atmospheric and astrophysical interest. We present highly correlated ab initio calculations (CCSD(T)-F12/CVTZ-F12) performed for the study of the FIR region of the spectrum. The molecule can be classified in the MSG G₁₈. It shows three interacting internal rotations corresponding to the two methyl groups and the OH alcoholic group. Torsional energy levels and subcomponents are determined variationally from a three-dimensional potential energy surface. For the classification of the computed levels, we apply symmetry considerations. Final torsional wave-functions denote the relevance of the interactions on the results. Perturbation theory is also used to determine the vibrational corrections of rotational constants. This project has received funding from the European Union\'s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 872081.

The broadband rotational spectra of ammonia-water (NH₃-H₂O) complex were measured in the frequency range from 50 to 250 GHz using a supersonic-jet emission spectrometer. The NH₃-H₂O complex exhibits two large amplitude motions (LAMs): almost free internal rotation of ammonia owing to very low torsional barrier ( ≈ 10 cm⁻¹), and the inversion of water characterized by relatively high barrier ( ≈ 700 cm⁻¹). Because of the latter and taking Doppler-limited resolution of spectrometer into account, we could not observe inversion tunneling splittings of a-type rotational transitions. In total, about 150 rotational transitions of NH₃-H₂O were assigned in this study. They were fitted together with the data from previous studiesP. A. Stockman, R. E. Bumgarner, S. Suzuki, & G. A. Blake, J. Chem. Phys. 96, 2496 (1992); G. T. Fraser & R.D. Suenram, J. Chem. Phys. 96, 7287 (1992)sing the "hybrid" Hamiltonian approachI. Kleiner & J. T. Hougen, J. Mol. Spectrosc. 368, 111255 (2020) The analysis is in progress as we are currently trying to modify the characteristics of supersonic expansion in order to achieve higher rotational temperatures and consequently to measure higher K_a transitions. The latest results will be presented.

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P. A. Stockman, R. E. Bumgarner, S. Suzuki, & G. A. Blake, J. Chem. Phys. 96, 2496 (1992); G. T. Fraser & R.D. Suenram, J. Chem. Phys. 96, 7287 (1992)u I. Kleiner & J. T. Hougen, J. Mol. Spectrosc. 368, 111255 (2020).

When the spectrum of R-carvone was collected at Missouri S&T in preparation for a three-wave mixing experiment, splittings within the rotational transitions were observed that were unassigned in both the original study of S-carvone by Moreno et al.Moreno, J. R. A.; Huet, T. R.; González, J. J. L. Struct Chem. 2013, 24, 1163.nd the monoterpenoid study by Loru et al.Loru, D.; Vigorito, A.; Santos, A. F. M.; Tang, J.; Sanz, M. E. Phys. Chem. Chem. Phys. 2019, 21, 26111-26116.s reported at the 75^th annual ISMS, it was discovered that these splittings were due to internal rotations caused by two non-equivalent methyl rotors. This prompted a reinvestigation into the pure rotational spectrum of R-carvone using chirped-pulse, Fourier transform microwave (CP-FTMW) spectroscopy within the 5-18 GHz region of the electromagnetic spectrum. Since initially reporting this finding, all parent species and singly substituted isotopologues for the six conformers of carvone have been analyzed using XIAMHartwig, H.; Dreizler, H. Z. Naturforsch. 1996, 51a, 923-932. Within this presentation, the results of the reinvestigation will be reported, including the experimentally derived molecular structures for the six conformers as well as the experimentally determined barrier heights to internal rotation. Moreno, J. R. A.; Huet, T. R.; González, J. J. L. Struct Chem. 2013, 24, 1163.a Loru, D.; Vigorito, A.; Santos, A. F. M.; Tang, J.; Sanz, M. E. Phys. Chem. Chem. Phys. 2019, 21, 26111-26116.A Hartwig, H.; Dreizler, H. Z. Naturforsch. 1996, 51a, 923-932..

Lignocellulose is the most abundantly available raw material on the Earth for the production of biofuels.C. H. Zhou, X. Xia, C. X. Lin, D. S. Tong and J. Beltramini, Chem. Soc. Rev., 2011, 40, 5588–5617he main challenge is to produce useful chemicals from it. A variety of chemicals and biomolecules are produced via the hydrothermal conversion of waste biomass. Among the produced products is levulinic acid (LA). This biomolecule is considered to be of the top 10 chemical compoundsT. Werpy, and G. Petersen, Top Value Added Chemicals from Biomass: Volume I, Results of Screening for Potential Candidates from Sugars and Synthesis Gas. United States: N. p., 2004.s it has an important potential to be considered as a platform chemical.G.C. Hayes, and C.R. Becer, 2020. Polymer Chemistry, 11, 4068-4077.t is used in the production of diverse chemical compounds in different area such as pharmaceuticals, herbicides, polymers, fuels etc.. Gas phase rotational studies permit a better understanding of intermolecular interactions that control the conformation landscape of molecules and their internal dynamics. We present herein, a broadband rotational study in jet-cooled conditions, of the relevant levulinic acid in the 6-18 GHz range. One conformer has been identified in the gas phase. The spectrum showed clearly that the lines were split. This splitting is due to the internal rotation of the methyl group. The A and E states lines were assigned and fitted, and the experimental barrier of the methyl torsion was determined.

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C. H. Zhou, X. Xia, C. X. Lin, D. S. Tong and J. Beltramini, Chem. Soc. Rev., 2011, 40, 5588–5617T T. Werpy, and G. Petersen, Top Value Added Chemicals from Biomass: Volume I, Results of Screening for Potential Candidates from Sugars and Synthesis Gas. United States: N. p., 2004.a G.C. Hayes, and C.R. Becer, 2020. Polymer Chemistry, 11, 4068-4077.I

Using the soon to be publicly available westerfit package, the rotational spectrum of meta-chloro-toluene has been re-examined. This program allows for treatment of a C_s molecule with an arbitrary-fold internal rotor and a single strong spin source which makes meta-chloro-toluene a promising test case for the code. Unlike other programs designed for internal rotation with spin effects, westerfit includes matrix elements off-diagonal in N rather than the perturbative treatment of the spin-rotation and quadrupole interactions. This allows fitting of all symmetrically allowed terms in both the spin-rotation and the quadrupole tensors as well as inclusion of any higher order terms coupling the large amplitude motion to the spin angular momentum. Meta-chloro-tolune is a particularly challenging case for internal rotor packages due to the low V₃ term coupled to a large V₆ term as well as the spin 3/2 nucleus. Previous attempts to fit this moleculeNair et al, J. Mol. Spec. 361 (2019), p1-7ere complicated by XIAM's limitations at very low barrier heights and perturbative quadrupole treatment. This work presents a more complete treatment of the meta-chloro-toluene spectrum and demonstrates comparisons between westerfit and other programs.

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Nair et al, J. Mol. Spec. 361 (2019), p1-7w