The rotational spectrum of 2-fluoroaniline was investigated using chirped pulse and Balle-Flygare Fourier transform microwave (FTMW) spectroscopy in the 8-19 GHz range. The spectrum contains transitions due to the ¹³C and ¹⁵N minor isotopologues which were detected in natural abundance for the first time. The ground state r₀ geometry of 2-fluoroaniline was derived from the spectrum and compares well with the r_e geometry derived from quantum chemical calculations at the B3LYP-D3BJ/cc-pVTZ level of theory. Previous room temperature microwave spectra,J. Mol. Struct.41(1977)315-317^,J. Mol. Spectrosc.114,13−22(1985)eport a tunneling splitting due to NH_2 J. Mol. Spectrosc.114,13-22(1985)r

Methacrylonitrile is believed to be an astrochemically relevant molecule due to the detection of acrylonitrile (C₃H₃N) in Saturn’s moon, Titan, and in the interstellar medium. We synthesized methacrylonitrile via the hydrocyanation and subsequent dehydration of acetone and obtained its rotational spectrum in the 130 – 360 GHz frequency region. The main isotopologue ground state has been least-squares fit to a sextic Hamiltonian accounting for internal rotation splitting from the 3-fold symmetric methyl rotor, and resulting spectroscopic constants compare well with those previously reported. The improved determination of centrifugal distortion constants improve the spectral prediction over a broad frequency range and thus the radioastronomical search for this molecule. Additionally, a study of pyrimidine, using 16 isotopologues, demonstrated that it is possible to determine very accurate semi-experimental equilibrium structures (r_e^SE) using multiple isotopic substitution combined with coupled-cluster calculations treating the vibration-rotation interaction and the electron mass correction. With the goal of such a structure determination for methacrylonitrile, we have analyzed the spectra of all singly-substituted heavy-atom isotopologues (¹³C and ¹⁵N), which were detectable at natural abundance, and least-squares fit them to sextic Hamiltonians. To obtain deuterated isotopologues, the synthesis of methacrylonitrile was modified by using partially deuterated or fully deuterated acetone to yield samples of varying deuterium incorporation. We have currently assigned the rotational spectra of 22 isotopologues, with additional isotopologues yet to be analyzed. The current r_e^SE will be presented and compared to theoretical r_e structures.

In a recent publication by Kraus and Frank,J. Phys. Chem. A 2018, 122, 21, 4894-49019 computational methods were used to predict the gas-phase geometries of 16 dimers and trimers whose structures we determined using rotational spectroscopy of isotopically substituted species. The experimental data set, called NCDT16, sampled various non-covalent interaction of four categories: dispersion dominated interactions, hydrogen bonded dimers, CH…π & π…π interactions, and a general category for trimers. For each method, a least-squares structure fit of experimental rotational constants was carried out using the respective predicted geometry as input, and the mean absolute errors were used to gauge the value of the method. The top performing methods of each category, as well as an overall category, are prescribed by the authors. This represents one of the few benchmarking studies of non-covalent interactions against experimental structures in the gas-phase. From the prescribed methods, we test the quality of the benchmarking study. With a focus specifically on CH…π interactions, we compare 7 complexes containing a halogenated methane and either acetylene or propyne (a C ≡ C bond). All compared complexes have structures determined by rotational spectroscopy. Our computational and fitting methods are outlined, and we discuss the strengths and weaknesses of such a study, with an emphasis on the benefits to spectroscopic research. J. Phys. Chem. A 2018, 122, 21, 4894-49018

l0pt Figure We are continuing our project of obtaining high resolution vibration-rotation spectra of propane isotopologues using the Far-IR beamline at the Canadian National Synchrotron (CLS). We have already reported on all the singly ¹³C and singly D substituted varieties as well as the 2,2-D₂ species at previous ISMS meetings (2017-19) and in a recent paper on 2-¹³C-Propane Daunt, Grzywacz, Western, Lafferty, Flaud, Billinghurst, and Hutchings, J. Mol. Structure, in press (doi:10.1016/j.molstruc.2020.127851). These studies have allowed us to determine ground state inertial and centrifugal distortion rotational constants for these molecules that have no pure rotational spectra in the literature except for the 6 lines reported by LideD. R. Lide, J. Chem. Physics 33, 1514-1518 (1960).n 1960 of normal propane and two ¹³C and D versions. In this talk we will present the high resolution spectra (0.00096 cm⁻¹) for the CCC skeletal bendings of CH₃CH₂CD₃, CD₃CH₂CD₃ and C₃D₈. These studies have yielded corrected observed band originsGayles and King, Spectrochim. Acta 21, 543-557 (1965); K. M. Gough, W. F. Murphy and K. Raghavachari, J. Chem. Phys. 87, 3332-3340 (1987).nd rotational constants for the three species. Preliminary values for each species are listed here in wavenumbers. CH₃CH₂CD₃: ν₉ = 335.664740(40), A₀ = 0.8185513(12), B₀ = 0.24400666(39), C₀ = 0.21852642(41); CD₃CH₂CD₃: ν₁₆ = 306.4, A₀ = 0.711202, B₀ = 0.213021, C₀ = 0.193244; C₃D₈: ν₉ = 303.936065(23), A₀ = 0.58742224(42), B₀ = 0.20872437(23), C₀ = 0.18588200(18).

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Footnotes:

Daunt, Grzywacz, Western, Lafferty, Flaud, Billinghurst, and Hutchings, J. Mol. Structure, in press (doi:10.1016/j.molstruc.2020.127851).. D. R. Lide, J. Chem. Physics 33, 1514-1518 (1960).i Gayles and King, Spectrochim. Acta 21, 543-557 (1965); K. M. Gough, W. F. Murphy and K. Raghavachari, J. Chem. Phys. 87, 3332-3340 (1987).a

Production of H₂ gas via water splitting reactions facilitated by solar light harvesting, can be a solution to the constant increase of energy demand. Water splitting is an endothermic process which requires about 2.69 eV per water molecule. High endothermicity of this process can be overcome by exploiting the sun light and using a suitable catalyst. Transition metal oxide (MO) catalysts are promising candidates for this process because of their multiple low-lying electronic states. The rate determining step in the water splitting reactions is often the activation of the O-H bonds. Here we have tested water activation strengths of several neutral and charged MOs computationally. The complicated electronic structures of these MOs forced us to perform multi-reference calculations. For these MOs the water activation process can be partitioned into three major processes. 1) Formation of the H₂O…OM interacting complex. 2) Surpass the transition state barrier which involve H-O bond cleavage of metal bound water. 3) HO-M-OH product formation. Due to the multiple low-lying excited states of these species, spin crossovers and electron excitation from ground to higher states are expected. Among the considered H₂O+[MoO]^−/+/2+ reactions, the anionic system is the best candidate for the water activation, which has a lower activation energy barrier and create a more stabilized product than interacting complex. On the contrary, MoO^2+/+ stabilizes the MoO^2+/+…H₂O interacting complex over products. A similar pattern was observed for the H₂O+[RuO]^−/0/+/2+ reactions. The suitability of RuO species for the water activation vary in RuO²⁺ < RuO⁺ < RuO < RuO⁻ order.

Only a few molecules with two iodine atoms have been studied using rotational spectroscopy probably due to the complex hyperfine splitting structure arising from the presence of two iodine nuclei. We report the high resolution rotational spectroscopic observation of the 1,1-diiodoethane for the first time. The spectrum was observed at 11-18 GHz frequency range in a jet-pulsed cavity-based Fourier transform microwave spectrometer. The observed transition frequencies were analyzed to yield the rotational constants, centrifugal distortion constants, the nuclear quadrupole coupling constants, and nuclear-spin rotation constants. The analysis was aided by quantum chemical calculations. Ab initio calculations were carried out at the CCSD(T) level along with the aug-cc-pVTZ-pp basis set, in order to help predict the molecular geometry. A single point calculation at MP2 level was performed to calculate the hyperfine parameters.

A computer algorithm is developed to narrow down the list of possible structural geometries of a molecule from the analysis of its isotopologue rotational constants. Based on Kraitchman's equation, the absolute values of the position coordinates of the atoms in a molecule may be obtained from the corresponding isotopologue rotational constants. The algorithm, in attempt to take a step further, narrows down the list of possible combinations of atom positions and bond connections within the molecule. Compared to a previous work by Mayer et al.Mayer, Kevin J., et al. "The Feasibility of Determining the Carbon Framework Geometry of a Molecule from Analysis of the CARBON-13 Isotopologue Rotational Spectra in Natural Abundance." 74th International Symposium on Molecular Spectroscopy. 2019.hich focused on carbon atoms, the algorithm extends the application to more atoms including oxygen, nitrogen, etc. More molecular geometry filters are integrated in the algorithm as well. Five filters involving interatomic distance, bond type, valence, bond angles, and coplanarity based on VSEPR theory are developed. As a result, the algorithm was able to narrow down the number of possible structures for Aspirin, a molecule with 13 non-hydrogen atoms, from 10¹⁰ to 110. However, the exact geometry of molecules could not be determined by the algorithm directly, especially when the molecule is large (usually more than five non-hydrogen atoms). In addition, large errors from Kraitchman's equation near the principle axes of the molecule leads to ambiguous results on those atoms. It leads to the belief that our current understanding may be insufficient to resolve the molecular geometry directly from the isotopologue rotational constants.

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Footnotes:

Mayer, Kevin J., et al. "The Feasibility of Determining the Carbon Framework Geometry of a Molecule from Analysis of the CARBON-13 Isotopologue Rotational Spectra in Natural Abundance." 74th International Symposium on Molecular Spectroscopy. 2019.w

In spectroscopic parlance, a linear triatomic molecule is one whose potential energy minimum occurs at a linear geometry. We have recently discussedT. Hirano, U. Nagashima, P. Jensen, H. Li, Journal of Molecular Spectroscopy 362 (2019) 29-36. URL https://doi.org/10.1016/j.jms.2019.05.005; P. Jensen, Canadian Journal of Physics (2020). URL https://doi.org/10.1139/cjp-2019-0395, and references therein.ow any linear triatomic molecule will be observed as being bent on ro-vibronic average in any ro-vibronic state. To provide further support for this idea we make here an ab initio calculation of the bending distribution functions for low lying vibrational states of the CO₂ molecule (which is well known to be linear in the sense mentioned above) in its ground electronic state. These functions have their maximum values at a non-linear geometry, and the value zero at linearity, despite the fact that the potential surface has its minimum value at linearity. They are in accord with experimental distribution functions inferred by analysis of Coulomb Explosion Imaging experiments.B. Siegmann, U. Werner, H. O. Lutz, R. Mann, Journal of Physics B: Atomic, Molecular and Optical Physics 35(17) (2002) 3755-3765. URL https://doi.org/10.1088%2F0953-4075%2F35%2F17%2F311; J. P. Brichta, S. J. Walker, R. Helsten, J. H. Sanderson, Journal of Physics B: Atomic, Molecular and Optical Physics 40(1) (2006) 117-129. URL https://doi.org/10.1088%2F0953-4075%2F40%2F1%2F011.hus in a femto-second `snapshot' of a room temperature ensemble of gas phase rotating-vibrating CO₂ molecules, none would be linear. The same can be said for any triatomic molecule or, for that matter, for any chain molecule with a linear equilibrium structure.

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Footnotes:

T. Hirano, U. Nagashima, P. Jensen, H. Li, Journal of Molecular Spectroscopy 362 (2019) 29-36. URL https://doi.org/10.1016/j.jms.2019.05.005; P. Jensen, Canadian Journal of Physics (2020). URL https://doi.org/10.1139/cjp-2019-0395, and references therein.h B. Siegmann, U. Werner, H. O. Lutz, R. Mann, Journal of Physics B: Atomic, Molecular and Optical Physics 35(17) (2002) 3755-3765. URL https://doi.org/10.1088%2F0953-4075%2F35%2F17%2F311; J. P. Brichta, S. J. Walker, R. Helsten, J. H. Sanderson, Journal of Physics B: Atomic, Molecular and Optical Physics 40(1) (2006) 117-129. URL https://doi.org/10.1088%2F0953-4075%2F40%2F1%2F011.T

Rotational constants in the ground states of benzene and its deuterated isotopologues were accurately determined by high-resolution spectroscopy [1]. It was demonstrated that the averaged bond length r_0,eff(C-H) is approximately identical to the r_0,eff(C-D). Bearing in mind that the experimentally observed rotational constants correspond to the averaged ro-vibrating structure projected onto each principal axis [2], we discussed this finding in terms of wavefunction for the local modes derived from the CCSD(T)/[aVQZ (C, H)] ab initio potential energy surface. Due to the anharmonicity in the C-H stretching motion, r_str,0(C-H) is calculated to be longer than r_str,0(C-D) by 0.0024 Å. Since the vibrationally averaged projection-angle of the C-H(D) bond with respect to the principal axis is larger for the C-H bond (having lighter H atom) than the C-D bond, the projected bond-lengths r_proj,0(C-H) in the out-of-plane and in-plane bending motions become shorter than r_proj,0(C-D) by 0.0017 Å and 0.0011 Å, respectively. Thus, in the sum of r_str,0 and r_proj,0, the difference in r_0,eff(C-H) and r_0,eff(C-D) becomes negligibly small value of 0.0004 Å, which explains why we observed r_0,eff(C-H) ≈ r_0,eff(C-D).
[1] S. Kunishige, M. Baba, et al., J. Chem. Phys., 143, 244302 (2015).
[2] T. Hirano, U. Nagashima, and M. Baba, J. Mol. Spectrosc., in press.

Connected to our efforts in characterizing substituted oxiranes for use as potential chiral tags for the conversion of enantiomeric molecules into spectroscopically distinct diastereomeric complexes for chiral analysis, we are exploring how argon binding to these species is modulated by varying the identity of the substituents on the epoxy ring. Previously studied systems generally showed close contacts primarily to atoms contained in the ring, but in complexes with cis-1,3,3,3-tetrafluoro-1,2-epoxypropane and oxiranylmethanol, multiple minima of similar energies are predicted by quantum chemistry calculations, including some with significant interactions between the argon atom and substituent atoms. Progress on assigning and analyzing the spectra of these complexes will be reported.

r0pt Figure The amino alcohol prolinol is a reduction product of the chiral amino acid proline, which is widely used as a chiral auxiliary in noted reactions. Up to date, only IR data for prolinol is available.J.J. Lee, S. Hesse, M.A. Suhm. Journal of Molecular Structure, 2010, 976, 397–404ere, we report the first high-resolution microwave study of this system. Two endo-like and exo-like conformations stabilized by strong intramolecular hydrogen bonds O-H···N have been detected in the supersonic expansion of our CP-FTMW technique.I. Uriarte, C. Pérez, E. Caballero-Mancebo, F. J. Basterretxea, A. Lesarri, J. A. Fernández and E. J. Cocinero, Chem. - A Eur. J., 2017, 23, 7156^,C. Calabrese, W. Li, G. Prampolini, L. Evangelisti, I. Uriarte, I. Cacelli, S. Melandri,and E. J. Cocinero, Angew.Chem., 2019, 131,8525–8530hese structures have been successfully identified by comparison of the experimental rotational and ^14N nuclear quadrupole coupling constants with those predicted theoretically. Given the high sensitivity reached in our experiment, the seven monosubstituted species of ^13C, ^15N and ^18O have also been observed in their natural abundance for both conformers, and the corresponding r_s C. Calabrese, W. Li, G. Prampolini, L. Evangelisti, I. Uriarte, I. Cacelli, S. Melandri,and E. J. Cocinero, Angew.Chem., 2019, 131,8525–8530T