Vinyl alcohol has two rotameric forms, known as syn- and anti-vinyl alcohol, where syn is the most stable. While both have been investigated by microwaveM. Rodler, J. Mol. Spec. 114, 23 (1985);S. Saito, Chem. Phys. Lett. 42, 3 (1976)nd far-infraredH. Bunn, R. Hudson, A. S. Gentleman, and P. L. Raston, ACS Earth Space Chem. DOI: 10.1021/acsearthspacechem.6b00008 (2017)pectroscopy, only the syn rotamer has been investigated by mid-infrared spectroscopyD-L Joo, A. J. Merer, D. J. Clouthier, J. Mol. Spec. 197, 68 (1999) This is due to the low anti rotamer population (15%) at room temperature, in addition to the closeness in proximity of the mid-infrared bands between the rotamers; this results in overlapping bands that are dominated by syn-vinyl alcohol absorptions. In this investigation we increase the anti-vinyl alcohol population to  40% by using a high temperature “pyrolysis” source, and eliminate the spectral overlap by recording the spectra at low temperature in helium nanodroplets. We observe a number of bands of both rotamers in the OH, CH, and CO stretching regions that display rotational substructure. A highlight of this work is the observation of a Fermi dyad in the OH stretching region of anti-vinyl alcohol. Anharmonic frequency calculations suggest that this is due to a near degeneracy of the OH stretching state (ν₁) with a triple combination involving ν₇, ν₈, and ν₉.

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Footnotes:

M. Rodler, J. Mol. Spec. 114, 23 (1985);S. Saito, Chem. Phys. Lett. 42, 3 (1976)a H. Bunn, R. Hudson, A. S. Gentleman, and P. L. Raston, ACS Earth Space Chem. DOI: 10.1021/acsearthspacechem.6b00008 (2017)s D-L Joo, A. J. Merer, D. J. Clouthier, J. Mol. Spec. 197, 68 (1999).

We report the infrared spectra of the n-propyl and i-propyl radicals measured in solid para-hydrogen (p-H₂) matrices at 3.2 K. n-Propyl and i-propyl radicals were produced via the 248 nm irradiation of matrices formed by co-depositing p-H₂ and either 1-Iodopropane (n-propyl) or 2-Iodopropane (i-propyl). Secondary photolysis was used to group spectral lines all due to the same species. Lines in the C-H stretching region were compared to previous work using the Helium Nanodroplet Isolation (HENDI) technique,Peter R. Franke, Daniel P. Tabor, Christopher P. Moradi, Gary E. Douberly, Jay Agarwal, Henry F. Schaefer III, and Edwin L. Sibert III, Journal of Chemical Physics 145, 224304 (2016).nd are in excellent agreement. In addition to a few lines previously measured in Ar matrices, we observe many previously unreported bands below 2000 cm⁻¹, which we attribute to the n-propyl and i-propyl radicals. The assignment of features below 2000 cm⁻¹are made via comparisons to anharmonic VPT2+K frequency computations.

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Footnotes:

Peter R. Franke, Daniel P. Tabor, Christopher P. Moradi, Gary E. Douberly, Jay Agarwal, Henry F. Schaefer III, and Edwin L. Sibert III, Journal of Chemical Physics 145, 224304 (2016).a

Scalar relativistic coupled cluster calculations are presented for the infrared spectrum of the xenon hexafluoride (XeF6) molecule in its Oh and C3v structures. Anharmonic contributions to vibrational frequencies and infrared intensities of the C3v structure are taken into account using second order vibrational perturbation theory (VPT2). The effect due to Fermi resonances in the VPT2 calculations is analyzed. A transition state linking the C3v and Oh structures has also been located in the potential energy surface. The fluxional character of the molecule is discussed.

Time-resolved resonance-enhanced Stokes and anti-Stokes Raman spectra of the thiocyanate dimer radical anion, (SCN)₂⁻, prepared by pulse radiolysis in water, have been obtained and interpreted in conjunction with theoretical calculations to provide detailed information on the molecular geometry and bond properties of the species. The structural properties of the radical are used to develop a molecular perspective on its thermochemistry in aqueous solution. Twenty-nine Stokes Raman bands of the radical observed in the 120-4200 cm⁻¹region are assigned in terms of the strongly enhanced 220 cm⁻¹fundamental, weakly enhanced 721 cm⁻¹, and moderately enhanced 2073 cm⁻¹fundamentals, their overtones and combinations. Calculations by range-separated hybrid (RSH) density functionals (ωB97x and LC-ωPBE) support the spectroscopic assignments of the 220 cm⁻¹vibration to a predominantly SS stretching mode and the features at 721 cm⁻¹and 2073 cm⁻¹to CS and CN stretching modes, respectively. The corresponding bond lengths are 2.705 (+0.036) Å, 1.663 (+0.001) Å and 1.158 (+0.002) Å. A first order anharmonicity of 1 cm⁻¹determined for the SS stretching mode suggests a convergence of vibrational states at an energy  1.5 eV, using the Birch-Sponer extrapolation. This value, estimated for the radical confined in solvent cage, compares well with the calculated gas-phase energy required for the radical (1.22 eV) to dissociate into SCN and SCN⁻ fragments. The enthalpy of dissociation drops to 0.63 eV in water when solvent dielectric effects on the radical and its dissociation products upon S-S bond scission are incorporated in the calculations. No frequency shift or spectral broadening was observed between light and heavy water solvents, indicating that the motion of solvent molecules in the hydration shell have no perceptible effect on the intramolecular dynamics of the radical. The Stokes and anti-Stokes Raman frequencies were found to be identical within the experimental uncertainty, suggesting that the frequency difference between the thermally relaxed and spontaneously created vibrational states of (SCN)₂⁻ in water is too small to be observable.

With increasing vibrational wavenumber, the density of states of a molecule is expected to rise dramatically, especially so when low wavenumber torsions (internal rotations) are present, as in the case of para-fluorotoluene (pFT). This in turn is expected to lead to more opportunities for coupling between vibrational modes, which is the driving force for intramolecular vibrational energy redistribution (IVR). Previous studiesC. J. Hammond, V. L. Ayles, D. E. Bergeron, K. L. Reid and T. G. Wright, J. Chem. Phys., 125, 124308 (2006)^,J. A. Davies, A. M. Green, A. M. Gardner, C. D. Withers, T. G. Wright and K. L. Reid, Phys. Chem. Chem. Phys., 16, 430 (2014)t higher energies have focussed on the two close lying vibrational levels at  1200 cm^-1 in the S_1 electronic state of pFT which were assigned to two zero−order bright states (ZOBSs), whose characters predominantly involve C−CH_3 and C−F stretching modes. A surprising result of these studies was that the photoelectron spectra showed evidence that IVR is more extensive following excitation of the C−F mode than it is following excitation of the C−CH_3 mode, despite these levels being separated by only 35 cm^-1. This observation provides evidence that the IVR dynamics are mode−specific, which in turn may be a consequence of the IVR route being dependent on couplings to nearby states that are only available to the C−F mode. In this work, in order to further investigate this behaviour, we have employed resonance−enhanced multiphoton ionisation (REMPI) spectroscopy and zero−kinetic−energy (ZEKE) spectroscopy to probe S_1 levels above 1000 cm^-1 in pFT. Such ZEKE spectra have been recorded via a number of S_1 J. A. Davies, A. M. Green, A. M. Gardner, C. D. Withers, T. G. Wright and K. L. Reid, Phys. Chem. Chem. Phys., 16, 430 (2014)a

We have employed resonance-enhanced multiphoton ionisation (REMPI) spectroscopy and zero-kinetic-energy (ZEKE) spectroscopy to investigate the first excited electronic singlet (S₁) state and the cationic ground state (D₀⁺) of para-fluorotoluene (pFT) and para-xylene (pXyl). Spectra have been recorded via a large number of selected intermediate levels, to support assignment of the vibration and vibration-torsion levels in these molecules and to investigate possible couplings. The study of levels in this region builds upon previous work on the lower energy regions of pFT and pXylA. M. Gardner, W. D. Tuttle, L. Whalley, A. Claydon, J. H. Carter and T. G. Wright, J. Chem. Phys., 145, 124307 (2016).^,A. M. Gardner, W. D. Tuttle, P. Groner and T. G. Wright, J. Chem. Phys., (2017, in press).^,W. D. Tuttle, A. M. Gardner, K. O’Regan, W. Malewicz and T. G. Wright, J. Chem. Phys., (2017, in press).nd here we are interested in how vibration-torsion (vibtor) levels might combine and interact with vibrational ones, and so we consider the possible couplings which occur. Comparisons between the spectra of the two molecules show a close correspondence, and the influence of the second methyl rotor in para-xylene on the onset of intramolecular vibrational redistribution (IVR) in the S₁ state is a point of interest. This has bearing on future work which will need to consider the role of both more flexible side chains of substituted benzene molecules, and multiple side chains.

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Footnotes:

A. M. Gardner, W. D. Tuttle, L. Whalley, A. Claydon, J. H. Carter and T. G. Wright, J. Chem. Phys., 145, 124307 (2016).\end A. M. Gardner, W. D. Tuttle, P. Groner and T. G. Wright, J. Chem. Phys., (2017, in press). W. D. Tuttle, A. M. Gardner, K. O’Regan, W. Malewicz and T. G. Wright, J. Chem. Phys., (2017, in press).a