Sulfanilamide (SA, 4-aminobenzenesulfonamide) is an antibacterial drug that interferes with the conversion of para-aminobenzoic acid (PABA) to folate, preventing the synthesis of folic acid (vitamin B9), essential in multiple carbon transfer reactions. Due to its importance, in this work, we characterize sulfanilamide in the isolation conditions of a supersonic expansion using Fourier transform microwave techniques assisted by laser ablation. A single conformer of the bare molecule, stabilized by an N-H•••O=S intramolecular interaction of the sulfonyl group, has been detected. Because the docking process is controlled by the difference in Gibbs free energy between the ligands solvated by the extracellular medium and the ligand interacting with the receptor’s active site, we have also studied the sulfanilamide’s microsolvation process. Interestingly, a single water molecule is enough to trigger a conformational switch.

In a collaborative effort with the University of Texas-Rio Grande Valley, a chirped pulse microwave (CP-FTMW) spectroscopy experiment was carried out on nonafluoro-tert-butyl alcohol (NFTBA) monomer from 5.5 to 18.75 GHz. Calculations were run in order to identify the lowest energy conformation and these will be compared to the experimentally determined structure. In addition to the structure, the spectrum of NFTBA exhibits large amplitude motion and these complexities will be examined and discussed. NFTBA exhibits high acidity comparable to carboxylic acids, and this presentation will draw comparisons between these two classes of molecules.

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 unreported in 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.t was discovered that these splittings were due to internal rotations caused by two non-equivalent methyl rotors. This promoted a re-investigation 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. Spectral analyses were performed using a combination of the SPFITPickett, H. M. J. Mol. Spectrosc. 1991, 148, 371-377.nd XIAMH. Hartwig and H. Dreizler, Z. Naturforsch 51a, 923-932 (1996).oftware packages. Current work on the parent and singly substituted isotopologue species for the EQ1 and EQ2 conformers will be reported. In addition, the potential energy barrier heights to internal rotation for both rotors have been analyzed and will be discussed.

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Moreno, J. R. A.; Huet, T. R.; González, J. J. L. Struct Chem. 2013, 24, 1163.I Pickett, H. M. J. Mol. Spectrosc. 1991, 148, 371-377.a H. Hartwig and H. Dreizler, Z. Naturforsch 51a, 923-932 (1996).s

Perillartine, a solid synthetic sweetener, has been brought into the gas phase using laser ablation techniques, and its conformational panorama has been studied using chirped-pulse Fourier transform microwave spectroscopy (LA-CP-FTMW). Four conformers are detected and characterized under the isolation conditions of the supersonic expansion. The four conformers present an E configuration of the C=N group with respect to the double bond of the ring. The observed structures are verified against the Shallenberger-Acree-Kier’s sweetness theory to shed light on the structure-sweetness relationship. The results show that for this particular oxime there is a deluge of possibilities to bind to the receptor.

We have great interest in the excited-state dynamics of trans-stilbene such as cis-trans isomerization in the electronic excited state. Zewail et al. reported the results of time-resolved spectroscopy and suggested its nonplanar structure in the ground S₀ state J. A. Syage, P. M. Felker, and A. H. Zewail, J. Chem. Phys. 81, 4685 (1984). In contrast, Pratt et al. concluded that the molecule is essentially planar both in the S₀ and S₁ states by analyzing the rotationally resolved high-resolution speoctrum of the S₁←S₀ 0₀⁰ band D. W. Pratt, W. L. Meerts et al., J. Phys. Chem. 94, 6 (1990). We observed the spectrum with much higher accuracy and quality, and re-determined the rotational constants by high-resolution spectrum of 0₀⁰ bannd. Although it is impossible to accurate determine the abosolute value of rotational constant A for the a-type transition, We could conclude that trans-stilbene is non-planar in the S₀ state. In addition to estimate the molecular structure from observed rotational constants, we developed program. By this program, we estimated that phenyl rings are rotated approximately ±10 degrees in S₀ state. Theoretical calculation using WB97XD functional provided the phenyl rings are rotated 14 degrees in S₀ state and 2.4 degrees in S₁ state. WB97XD functional evaluate steric repulsion between H atoms of ortho-position in a phenyl ring and in an ethylene part by dispersion force potential semi-eprically. This result support non-planar structure revealed from the observed rotational constants.

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J. A. Syage, P. M. Felker, and A. H. Zewail, J. Chem. Phys. 81, 4685 (1984).. D. W. Pratt, W. L. Meerts et al., J. Phys. Chem. 94, 6 (1990)..

l0pt Figure We continue our project of recording spectra and ro-ibrational analyses of propane isotopologues to determine ro-vibrational constants for this family of molecules. No MW, mm or sub-mm studies exist as of yet. IR/R spectra of propane-D₅ do not appear to have ever been reported on in the literature. There are only low/medium resolution data on the -D₇ species.Gough, Murphy and Raghavachari, J.Chem. Phys. 87, 3332 (1987) and refs. thereine acquired survey and high resolution (0.002-0.00096 cm⁻¹) synchrotron IR data at the CLS facility in Saskatoon for the -D₅ bands. We also now have preliminary values of its rotational constants from the B-type CCC bending mode near 332.7 cm⁻¹. For the -D₇ species we have preliminary analyses of the B-type ν₁₄(A') CCC bend near 305.24 cm⁻¹and the ν₁₃ (A') C-type band near 579.34 cm⁻¹. The figure at the left is a part of the R-side of the ν₁₃ band for Propane-D₇. Observed spectrum taken at 0.00096cm⁻¹resolution plotted above the PGOPHERC. M. Western, B. E. Billinghurst PCCP 21, 13986 (2019) and refs. therein.imulation.

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Gough, Murphy and Raghavachari, J.Chem. Phys. 87, 3332 (1987) and refs. thereinW C. M. Western, B. E. Billinghurst PCCP 21, 13986 (2019) and refs. therein.s

The detection of acrylonitrile (C₃H₃N) in Titan's atmosphere and the interstellar medium suggests methacrylonitrile may also have astronomical relevance. To aid in the astronomical observation, we synthesized methacrylonitrile via the hydrocyanation and subsequent dehydration of acetone and obtained its rotational spectrum from 6 – 40 GHz and 130 – 500 GHz. The ground vibrational state of the main isotopologue has been least-squares fit to a sextic Hamiltonian accounting for internal rotation splitting, and the resulting spectroscopic constants compare well with previous literature. The increase in the measured frequency range improved the determination of centrifugal distortion constants, and thus enhances the possibility of detection via radioastronomy. Additionally, a semi-experimental equilibrium structure (r_e^SE) for methacrylonitrile is sought after due to its small molecular size and accessibility to a wide range of isotopologues. We analyzed the spectra from 6 – 40 GHz and 130 – 360 GHz of all singly-substituted heavy-atom isotopologues (¹³C and ¹⁵N), which were detectable at natural abundance, and least-squares fit them to sextic Hamiltonians accounting for internal rotation. The synthesis of methacrylonitrile was modified by using partially deuterated or fully deuterated acetone to yield samples of varying deuterium incorporation. We will present our analysis of 23 isotopologues, including the main isotopologue, and the resulting (r_e^SE) structure.

The A ← X electronic transition spectra of halogen diatomic molecules have been measured to determine the molecular constants and the parameters of potential energy by various researchers.Selin et al, Ark. Fys. 21 (1962) 479.^,Coxon et al, JMS 79 (1983) 363, 380.^,Heddrich et al, JMS 79 (1992) 384.wrapfigurer[10pt]0.3

D-Penicillamine, a drug widely used to treat Wilson’s disease, removes copper excess from the human body by acting as a chelating agent. In the present work, we address unveiling this molecule's three-dimensional structure as a first approach to shed light on its mechanism of action. Using a laser ablation source, we have transferred solid D-Penicillamine to the gas phase by laser ablation LA and probed it employing CP-FTWM spectroscopy in the isolated conditions of a supersonic jet. Two dominant conformers of the D-Penicillamine have been identified so far.

The HHe₃⁺ cation is a model system for solvated triatomic molecules, which consists of a (quasi)linear HHe₂⁺ core (chromophore) and a weakly-bound solvating He.Mol. Phys. 2019, 117, 9-12, 1559-1583; J. Phys. Chem. Lett. 2019, 10, 5325-5330; Phys. Chem. Chem. Phys. 2020, 22, 22885-22888he equilibrium structure is T-shaped, but the "quantum" structure is very different, showing large-scale nuclear delocalization. In order to study the structure and dynamics of HHe₃⁺ we performed path-integral molecular dynamics and variational nuclear-motion computations,J. Chem. Phys. 2009, 130, 134112.; J Chem. Phys. 2011, 134, 074105.; J. Chem. Phys. 2017, 147, 134101.ased on a new, highly accurate, neural-network potential-energy surface.Angew. Chem. Int. Ed. 2017, 56, 12828; J. Chem. Theo. Comp. 2020, 16, 88.; https://www.theochem.rub.de/go/rubnnet4md.htmle tested the new potential on the HHe₂⁺ cation. The computed rovibrational transitions have excellent agreement with experimental data, showing the high quality of the potential. As to the HHe₃⁺, we determined the vibrational states below and above the dissociation limit, corresponding to the solvating He and the chromophore, respectively. The computed chromophore vibrational frequencies have good agreement with the experimental results. Note that, the frequencies of the chromophore vibrations are significantly shifted compared to that of the HHe₂⁺, because the intermolecular bond is relatively strong. In order to investigate the "quantum" structure, we computed and plotted the nuclear density, which shows the spatial distribution of solvating He with respect to the chromophore. The nuclear density was obtained from path integral molecular dynamics computations and the vibrational wave functions from the nuclear-motion computation. The plots reveal that the true shape of the complex is completely different from the equilibrium structure: the solvating He is fully delocalized, forming a torus around the central proton even in the vibrational ground state. Delocalization is observed for each state, and its exact pattern reflects the type of vibrational excitation.

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Mol. Phys. 2019, 117, 9-12, 1559-1583; J. Phys. Chem. Lett. 2019, 10, 5325-5330; Phys. Chem. Chem. Phys. 2020, 22, 22885-22888T J. Chem. Phys. 2009, 130, 134112.; J Chem. Phys. 2011, 134, 074105.; J. Chem. Phys. 2017, 147, 134101.b Angew. Chem. Int. Ed. 2017, 56, 12828; J. Chem. Theo. Comp. 2020, 16, 88.; https://www.theochem.rub.de/go/rubnnet4md.htmlW

Understanding the rotational structure of molecular spectra requires high resolution and high-frequency accuracy. Furthermore, a capability of high-speed, wide-range spectral scan is strongly desired. We have developed a mid-infrared Doppler-free saturation absorption spectroscopy apparatus using a continuous-wave optical parametric oscillator (CW-OPO).D. B. Foote, M. J. Cich, W. C. Hurlbut, U. Eismann, A. T. Heiniger, and C. Haimberger, "High-resolution, broadly-tunable mid-IR spectroscopy using a continuous-wave optical parametric oscillator" Opt. Express 29, 5295-5303 (2021)ere we report a comprehensive spectral scan of the ν₃ = 1 band of methane (CH₄). The absolute frequency calibration was achieved using previously reported transition frequencies determined using optical frequency combs,M. Abe, K. Iwakuni, S. Okubo, and H. Sasada, "Accurate transition frequency list of the ν₃ band of methane from sub-Doppler resolution comb-referenced spectroscopy," J. Opt. Soc. Am. B 30, 1027-1035 (2013)hile a home-build Fabry-Pérot etalon was used for relative frequency calibration. A linewidth of less than 5 MHz has been reached, and the frequency accuracy is estimated to be better than 1 MHz, both of which can be further improved. We have successfully locked the frequency of the OPO to a Doppler-free line of CH₄ using a top-of-fringe locking method. A cavity-enhanced double-resonance spectroscopy apparatus is under construction. It combines the Doppler-free saturation absorption setup and an existing continuous-wave cavity ring-down (CW-CRDS) spectroscopy apparatus. The first mid-infrared photon from the frequency-locked OPO pumps the CH₄ molecule to the ν₃ = 1 vibrational levels, followed by a further excitation to high polyads using a Ti:Saphire ring laser. D. B. Foote, M. J. Cich, W. C. Hurlbut, U. Eismann, A. T. Heiniger, and C. Haimberger, "High-resolution, broadly-tunable mid-IR spectroscopy using a continuous-wave optical parametric oscillator" Opt. Express 29, 5295-5303 (2021)H M. Abe, K. Iwakuni, S. Okubo, and H. Sasada, "Accurate transition frequency list of the ν₃ band of methane from sub-Doppler resolution comb-referenced spectroscopy," J. Opt. Soc. Am. B 30, 1027-1035 (2013)w

For planar aromatic hydrocarbons, intersystem crossing to the triplet state is expected to be very slow according to El Sayed's ruleM. Baba, N. Nakayama, et al., J. Chem. Phys. 130, 134315 (2009).M. Baba, J. Phys. Chem. A 115, 9514 (2011).. The fluorescence lifetime in the S₁ state of dibenzothiophene is remarkably shorter compared with the analogous molecules such as dibenzofuran. Pratt et al. suggested that the main fast process was intersystem crossing on the basis of the result of high-resolution laser spectroscopyL. Alvarez-Valtierra, John T. Yi, and David W. Pratt, J. Phys. Chem. A 113, 2261(1990). We observed the high-resolution spectrum in the external magnetic field in order to confirm the contribution of the triplet state. However, no change has been found in the spectrum up to 1.0 Tesla, indicating that the intersystem crossing is slow and is not the main process for the fluorescence decay in the S₁ state of dibenzothiophene. It should be noted that the spectral feature of the S₁ ← S₀ 0₀⁰ band of dibenzothiophene is b-type, whereas that of dibenzofuran is a-type. The relatively faster decay is considered to be the result of different character in the S₁ elecronic state. Several electronic excited states are expected to be located in the lower energy regionM. Baba, T. Katori, M. Kawabata, S. Kunishige, and T. Yamanaka, J. Phys. Chem. A 117, 13524 (2013). Ab initio theoretical calculation of B3LYP/6-311G+(2d,p) accurately reproduced the experimental values of rotational constants and excitation energy. The S₁ state has been assigned to ¹A₁, which is consistent with the fact that the S₁ ← S₀ transition is b-type.

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Footnotes:

M. Baba, N. Nakayama, et al., J. Chem. Phys. 130, 134315 (2009).

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Footnotes:

L. Alvarez-Valtierra, John T. Yi, and David W. Pratt, J. Phys. Chem. A 113, 2261(1990).. M. Baba, T. Katori, M. Kawabata, S. Kunishige, and T. Yamanaka, J. Phys. Chem. A 117, 13524 (2013)..