With Pulsed-Jet Fourier Transform MicroWave (PJ-FTMW) spectroscopy and Stark modulated Free Jet Millimeter-Wave absorption (FJ-AMMW) spectroscopy, the rotational spectra of two conformers of 1,2-Dimethoxyethane were identified and characterized. Besides the normal species, the spectra of all the mono-substituted ¹³C isotopologues in natural abundance were also measured. By fitting the rotational transitions split by the methyl internal rotations using both XIAM and ERHAM programs, the spectroscopic parameters were obtained and compared. The rotational constants indicated the conformers to be TGT and TGG', respectively. With the rotational constants of the normal and ¹³C species, the coordinates of the substituted carbon atoms could be calculated with Kraitchmann’s equations. The carbon-frameworks further confirmed the assignment of the two conformations. The V₃ barriers of the two methyl groups’ internal rotations were also experimentally determined.

Accurate predictions of spectroscopic constants for non-rigid molecules are particularly challenging for ab initio theory. For all but the smallest systems, "brute force" diagonalization of the full rovibrational Hamiltonian is computationally prohibitive, leaving us at the mercy of perturbative approaches. However, standard perturbative techniques, such as second order vibrational perturbation theory (VPT2), are based on the approximation that a molecule makes small amplitude vibrations about a well defined equilibrium structure. Such assumptions are physically inappropriate for non-rigid systems. In this talk, we will describe extensions to curvilinear vibrational Møller-Plesset perturbation theory (VMP2) that account for rotational and rovibrational effects in the molecular Hamiltonian. Through several examples, we will show that this approach provides predictions to nearly microwave accuracy of molecular constants including rotational and centrifugal distortion parameters, Coriolis coupling constants, and anharmonic vibrational and tunneling frequencies.

The radical spectrum, first observed by Herzberg and Ramsay,Herzberg and Ramsay, J. Chem.\ Phys. 20 (1952) 347s dominated by a strong Renner-Teller effectDressler and Ramsay, Phil.\ Trans. R. Soc. A 25 (1959) 553iving rise to two electronic states: the bent X ²B₁ ground state and the quasi-linear A ²A₁ excited state. The radical has been the subject of numerous high-resolution investigations and its electronic and ro-vibrational transitionsHadj Bachir, Huet, Destombes, and Vervloet, J. Molec. Spectrosc.  193 (1999) 326; McKellar, Vervloet, Burkholder, and Howard, J. Molec. Spectrosc. 142 (1990) 319; Morino and Kawaguchi, J. Molec. Spectrosc. 182 (1997) 428ave been measured. Using synchrotron radiation, new rotational transitions have been recently recorded and a value of the rotational quantum number N as large as 26 could be reached.Martin-Drumel, Pirali, and Vervloet, J. Phys. Chem. A 118 (2014) 1331n the X ²B₁ ground state, the radical behaves like a triatomic molecule displaying spin-rotation splittings. Due to the lightness of the molecule, a strong coupling between the overall rotation and the bending mode arises whose effects increase with N and lead to the anomalous centrifugal distortion evidenced in the new measurements.^d In this talk the Bending-Rotation approachCoudert, J. Molec. Spectrosc. 165 (1994) 406eveloped to account for the anomalous centrifugal distortion of the water molecule is modified to include spin-rotation coupling and applied to the fitting of high-resolution data pertaining to the ground electronic state of . A preliminary line position analysis of the available data^c,d allowed us to account for 1681 transitions with a unitless standard deviation of 1.2. New transitions could also be assigned in the spectrum recorded by Martin-Drumel et al.^d In the talk, the results obtained with the new theoretical approach will be compared to those retrieved with a Watson-type Hamiltonian and the effects of the vibronic coupling between the ground X ²B₁ and the excited A ²A₁ electronic state will be discussed.

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Herzberg and Ramsay, J. Chem.\ Phys. 20 (1952) 347i Dressler and Ramsay, Phil.\ Trans. R. Soc. A 25 (1959) 553g Hadj Bachir, Huet, Destombes, and Vervloet, J. Molec. Spectrosc.  193 (1999) 326; McKellar, Vervloet, Burkholder, and Howard, J. Molec. Spectrosc. 142 (1990) 319; Morino and Kawaguchi, J. Molec. Spectrosc. 182 (1997) 428h Martin-Drumel, Pirali, and Vervloet, J. Phys. Chem. A 118 (2014) 1331I Coudert, J. Molec. Spectrosc. 165 (1994) 406d

There are three CH stretch modes in the CH₃OO·, namely the totally symmetric stretch, ν₂, the out-of-phase symmetric stretch, ν₁, and the antisymmetric stretch, ν₉. However, only two strong partially rotationally resolved vibrational transitions are observed in the CH stretch region of the infrared spectrum of CH₃OO·. Moreover, the Q-branches of both bands are significantly broader than the simulations using an asymmetric rigid rotor model. Previously, the rotational contour of the ν₂ band in the experimental spectrum has been simulated by considering the fundamental as well as sequence band transitions involving torsionally excited levels populated at room temperatureK.-H. Hsu, Y.-H. Huang, Y.-P. Lee, M. Huang, T. A. Miller and A. B. McCoy J. Phys. Chem. A, 2016, 120 (27), 4827 Using a four dimension Hamiltonian that involves the three CH stretches and the CH₃ torsion, the torsional sequence bands of the ν₂ stretch were calculated to be slightly shifted from the origin band as a result of the couplings between the CH stretches and CH₃ torsion which are particularly large due to an accidental degeneracy between the combination level involving the ν₂ stretch and n quanta in the CH₃ torsion and the combination level involving the ν₁ or ν₉ stretch and n−1 quanta in the CH₃ torsion. In this study we focus on the part of CH₃OO· vibrational spectrum containing the ν₁ and ν₉ bands. Along with the 4-dimensional Hamiltonian which was used to simulate the spectra in the ν₂ region, we analyze the effect of torsion-stretch couplings on the ν₁ and ν₉ bands based on the model developed by HougenJ.-T. Hougen J. Mol. Spec., 2001, 207, 60o describe methanol. To account for the accidental degeneracies in CH₃OO, we extend the previous model to include the combination levels involving the ν₂ stretch and the CH₃ torsion. Unlike the torsional sequence bands and fundamental of ν₂, the tunneling splittings of the torsional sequence bands and fundamentals of ν₁ and ν₉ have different signs, which results in the weak intensity of ν₁ fundamental and broadening in the rotational contour of the torsional sequence bands of ν₉.The simulation of the ν₉ and ν₁ bands including the torsional sequence bands using the parameters which are consistent with the ones used in the simulation of the ν₂ band is in good agreement with the experimental spectrum. K.-H. Hsu, Y.-H. Huang, Y.-P. Lee, M. Huang, T. A. Miller and A. B. McCoy J. Phys. Chem. A, 2016, 120 (27), 4827. J.-T. Hougen J. Mol. Spec., 2001, 207, 60t

The challenging quantum dynamical description of the CH₄·H₂O complex has been solved variationally¹ to provide theoretical explanation and assignment to the high-resolution spectroscopic measurements of the methane-water dimer carried out some twenty years ago.² The computational results are in excellent agreement with the reported experimental transitions and the experimentally observed reversed rovibrational sequences, i.e., formally negative rotational excitation energies, are also obtained in the computations. In order to better understand the origin of these peculiar features in the energy-level spectrum, we studied³ all four possible combinations of the light and heavy isotopologues of methane and water and analyzed their rovibrational states using two limiting model systems: the rigidly rotating (RR) molecule and the coupled rotor (CR) system corresponding to the coupling of the two rotating monomers. All rovibrational quantum dynamical computations^1,3 were carried out with rigid monomers and J = 0,1,2 total angular momentum quantum numbers using the fourth-age quantum chemical code GENIUSH^4,5 and two different methane-water potential energy surfaces (PES).^6,7 The numerical and formal analysis of the wave functions give insight into a fascinating complex world worth for further theoretical and experimental inquiries. ¹ J. Sarka, A. G. Császár, S. C. Althorpe, D. J. Wales and E. Mátyus, Phys. Chem. Chem. Phys. 18, 22816 (2016). ² L. Dore, R. C. Cohen, C. A. Schmuttenmaer, K. L. Busarow, M. J. Elrod, J. G. Loeser and R. J. Saykally, J. Chem. Phys. 100, 863 (1994). ³ J. Sarka, A. G. Császár, and E. Mátyus, Phys. Chem. Chem. Phys. accepted for publication (2017). ⁴ E. Mátyus, G. Czakó, and A. G. Császár, J. Chem. Phys. 130, 134112 (2009). ⁵ C. Fábri, E. Mátyus, and A. G. Császár, J. Chem. Phys. 134, 074105 (2011). ⁶ O. Akin-Ojo and K. Szalewicz, J. Chem. Phys. 123, 134311 (2005). ⁷ C. Qu, R. Conte, P. L. Houston and J. M. Bowman, Phys. Chem. Chem. Phys. 17, 8172 (2015).

Tunneling switching is a fundamental phenomenon of interest in molecular quantum dynamics including also chiral molecules and parity violation.M. Quack , Fundamental Symmetries and Symmetry Violations from High-resolution Spectroscopy, Handbook of High Resolution Spectroscopy, M. Quack and F. Merkt eds.,John Wiley & Sons Ltd, Chichester, New York, 2001, vol. 1, ch. 18, pp. 659-722.^,R. Prentner, M. Quack, J. Stohner and M. Willeke, J. Phys. Chem. A 119, 12805−12822 (2015).^,S. Albert, Z. Chen, C. Fábri, R. Prentner M. Quack and D. Zindel, paper at this meeting.euterated phenols have been identified as prototypical achrial candidates.S. Albert, Ph. Lerch, R. Prentner and M. Quack, Angew. Chem. Int. Ed. 52, 346-349 (2013).e report the high resolution spectroscopic investigation of the ortho-D-phenol in the GHz and THz ranges following our recent discovery of tunneling switching in its isotopomer meta-D-phenol.S. Albert, Z. Chen, C. Fábri,P. Lerch, R. Prentner and M. Quack, Mol.Phys. 114, 2751-2768 (2016) and 71st International Symposium on Molecular Spectroscopy, Urbana-Champaign, USA, June 20-24, Talk FE04 (2016).ere we report new results on ortho-D-phenol.The pure rotational spectra were recorded in the range of 72-117 GHz and assigned to the syn- and anti- structures in the ground and the first excited torsional states. Specific torsional states were assigned based on a comparison of experimental rotational constants with the quasiadiabatic channel reaction path Hamiltonian (RPH) calculations. The torsional fundamental at  308 cm⁻¹ and the first hot band at 275 cm⁻¹ were subsequently assigned. The analyses of pure rotational and rovibrational spectra shall be discussed in detail in relation to possible tunneling switching. M. Quack , Fundamental Symmetries and Symmetry Violations from High-resolution Spectroscopy, Handbook of High Resolution Spectroscopy, M. Quack and F. Merkt eds.,John Wiley & Sons Ltd, Chichester, New York, 2001, vol. 1, ch. 18, pp. 659-722.\end R. Prentner, M. Quack, J. Stohner and M. Willeke, J. Phys. Chem. A 119, 12805−12822 (2015). S. Albert, Z. Chen, C. Fábri, R. Prentner M. Quack and D. Zindel, paper at this meeting.D S. Albert, Ph. Lerch, R. Prentner and M. Quack, Angew. Chem. Int. Ed. 52, 346-349 (2013).W S. Albert, Z. Chen, C. Fábri,P. Lerch, R. Prentner and M. Quack, Mol.Phys. 114, 2751-2768 (2016) and 71st International Symposium on Molecular Spectroscopy, Urbana-Champaign, USA, June 20-24, Talk FE04 (2016).H

The b-type band near 1583 cm⁻¹has been assigned for m ≤ 3, K"_a ≤ 10, J" ≤ 20. The ground state combination differences derived from these assigned levels were fit with the RAM36 program with an RMS deviation of 0.0006 cm⁻¹. The upper state levels are split into multiplets by perturbations. A subset of the available upper state combination differences for m = 0, K′_a ≤ 7, J′ ≤ 10 were fit with the same program, but with rather poorer precision (0.01 cm⁻¹) than for the ground state.

The S₁ electronic state and ground state of the cation of para-fluorotoluene (pFT) have been investigated using resonance-enhanced multiphoton ionization (REMPI) spectroscopy and zero-kinetic-energy (ZEKE) spectroscopy.A. M. Gardner, W. D. Tuttle, L. Whalley, A. Claydon, J. H. Carter and T. G. Wright, J. Chem. Phys., 145, 124307 (2016).ere we focus on the low wavenumber region where a number of “pure” torsional, fundamental vibrational and vibration-torsional levels are expected; assignments of observed transitions are discussed, which are compared to results of published work on toluene (methylbenzene) from the Lawrance group.J. R. Gascooke, E. A. Virgo, and W. D. Lawrance J. Chem. Phys., 143, 044313 (2015).he similarity in the activity observed in the excitation spectrum of the two molecules is striking.

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A. M. Gardner, W. D. Tuttle, L. Whalley, A. Claydon, J. H. Carter and T. G. Wright, J. Chem. Phys., 145, 124307 (2016).H J. R. Gascooke, E. A. Virgo, and W. D. Lawrance J. Chem. Phys., 143, 044313 (2015).T

The electronic transition S₁ ← S₀ of p-xylene (pXyl) has been observed by REMPI spectroscopy.AM Gardner, WD Tuttle, P. Groner, TG Wright, J. Chem. Phys., submitted Dec 2016ts analysis required a detailed investigation of the molecular symmetry of pXyl whose methyl groups are almost free internal rotors. The molecular symmetry group of pXyl has 72 operators.P Groner, JR Durig, J. Chem. Phys., 66 (1977) 1856his group, called [33]D_2h, is isomorphic to G₃₆(EM),PR Bunker, P Jensen, Molecular Symmetry and Spectroscopy (1998, NRC Research Press, Ottawa, 2nd ed.)he double group for ethane and dimethyl acetylene even though it is NOT a double group for pXyl. Loosely speaking, the group symbol, [33]D_2h, indicates that is for a molecule with two threefold rotors on a molecular frame with D_2h point group symmetry. The transformation properties of the (i) free internal rotor basis functions for the torsional coordinates, (ii) the asymmetric rotor (Wang) basis functions for the Eulerian angles, (iii) nuclear spin functions, (iv) potential function, and (v) transitions dipole moment functions were determined. The forms of the torsional potential in the S₀ and S₁ states and the dependence of the first order torsional splittings on the potential coefficients have been obtained.

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AM Gardner, WD Tuttle, P. Groner, TG Wright, J. Chem. Phys., submitted Dec 2016I P Groner, JR Durig, J. Chem. Phys., 66 (1977) 1856T PR Bunker, P Jensen, Molecular Symmetry and Spectroscopy (1998, NRC Research Press, Ottawa, 2nd ed.)t

Insight gained from examining the “pure” torsional, vibrational and vibration-torsional (vibtor) levels of the single rotor molecules: toluene (methylbenzene)J. R. Gascooke, E. A. Virgo, and W. D. Lawrance, J. Chem. Phys., 143, 044313 (2015).nd para-fluorotoluene (pFT),A. M. Gardner, W. D. Tuttle, L. Whalley, A. Claydon, J. H. Carter and T. G. Wright, J. Chem. Phys., 145, 124307 (2016).s applied to the double rotor para-xylene (p-dimethylbenzene) molecule .A. M. Gardner, W. D. Tuttle, P. Groner and T. G. Wright, J. Chem. Phys., (2017, in press).esonance-enhanced multiphoton ionization (REMPI) spectroscopy and zero-kinetic-energy (ZEKE) spectroscopy are employed in order to investigate the S₁ and ground cationic states of para-xylene. Observed transitions are assigned in the full molecular symmetry group (G₇₂) for the first time.

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Footnotes:

J. R. Gascooke, E. A. Virgo, and W. D. Lawrance, J. Chem. Phys., 143, 044313 (2015).a A. M. Gardner, W. D. Tuttle, L. Whalley, A. Claydon, J. H. Carter and T. G. Wright, J. Chem. Phys., 145, 124307 (2016).i A. M. Gardner, W. D. Tuttle, P. Groner and T. G. Wright, J. Chem. Phys., (2017, in press).R