The microwave spectrum of teflic acid (TeF₅OH) in the range of 3 to 25 GHz was analyzed. Though teflic acid is an asymmetric top in its equilibrium structure, it behaves like a symmetric top because of the OH group internal rotation. The strongest transitions in the spectrum originate from the ¹³⁰TeF₅OH, ¹²⁸TeF₅OH and ¹²⁶TeF₅OH species as shown in the figure below. The TeF₅¹⁸OH, TeF₅OD and TeF₅¹⁸OD isotopologues were also analyzed. From the rotational constants of the different istopologues and with help of quantum chemical calculations a semi empirical equilibrium structure of teflic acid was determined. The Te-O equilibrium bondlength was determined with accuracy to the hundredth of an angstrom. [0]r[-90pt]0pt Figure

CO is the second most abundant molecule in the universe. Precise spectrum of the carbon monoxide molecule is great importance in astrophysical observation and in the test of the quantum chemistry model. Thirty-nine ro-vibrational transitions of ¹²C¹⁶O in the second overtone band were measured by a comb-locked cavity ring-down spectrometer. The line positions were determined with kHz accuracy, or relatively 10⁻¹² level, which is over two orders of magnitude more accurate than previous Doppler-limited studies. Comparisons of the line positions determined in this work with literature experimental values and the calculations by the Dunham-Watson model are given. The bond length in the second overtone vibrational state was determined for carbon monoixde. The calculated pure rotational line positions agree with the experimental values recorded by lamb-dip spectrometer within the experimental uncertainties.

Next autumn, the redefinition of the international System of Units (SI) will be accepted by the General Conference on Weights and Measures. This major reform will establish a new definition of units in terms of a set of 7 defining constants. The temperature unit, the kelvin, the definition of which is currently based on the triple point of water (TPW), will for example be redefined by fixing the value of the Boltzmann constant k_B. For the implementation of the new kelvin, various primary thermometry methods are currently being developed such as Doppler-broadening thermometry (DBT), acoustic gas thermometry, Johnson noise thermometry, dielectric constant gas thermometry, etc... We have previously proposed and developped the DBT method and have used it to demonstrate an accurate determination of k_BC. Daussy et al., First direct determination of the Boltzmann constant by an optical method, Phys. Rev. Lett. 98, 250801 (2007).^S. Mejri et al., Measuring the Boltzmann constant by mid−infrared laser spectroscopy of ammonia, Metrologia 52, S314 (2015). Once k_ fixed in the new SI, DBT will become a primary spectroscopic method for thermodynamic temperature measurements and thus for the implementation of the new kelvin. DBT is based on the precise measurement of the Doppler broadening of absorption line of a gaz phase atomic or molecular species, an ammonia ro−vibrational transition in the mid−infrared range (10m) in our case, combined with some highly accurate modeling of the line profile.We are currently developing DBT in the temperature range 300−430K, in order to demonstrate its potential and study its limitations beyond the temperature of the TPW. We will present our progress towards temprature measurements with uncertainties at the 25ppm level. The existing set−up (previously used for the determination of k_ S. Mejri et al., Measuring the Boltzmann constant by mid-infrared laser spectroscopy of ammonia, Metrologia 52, S314 (2015)..

Parity violation (PV) has never been observed in chiral molecules. Caused by the weak nuclear force, PV should lead to a tiny energy difference between the enantiomers of a chiral molecule, and in turn to frequency differences in the rovibrational spectra of the two enantiomers of a chiral molecule. A successful PV measurement will shed some light on the origins of biomolecular homochirality. It can also constitute a test of the standard model in the low-energy regime and a probe of physics beyond it, and serve as a stringent benchmark in relativistic quantum chemistry calculations. We present our ongoing work towards developing the technologies needed for measuring PV in chiral molecules via Ramsey interferometry in the mid-infrared. This includes amongst other things developing frequency stabilised quantum cascade lasers calibrated against primary standards and a buffer-gas source of organo-metallic species of interest for a PV measurement formed using laser ablation of solid-state molecules in a cryogenic cell containing gaseous helium at 4 K. We also present the results of preliminary spectroscopic investigations conducted on various species, in particular methyltrioxorhenium (MTO), an achiral test molecule from which promising chiral derivatives have recently been synthesized. We report on the high-resolution spectroscopy of MTO, both in cells and in molecular beams, at various temperatures and resolutions.

H-bonded complexes between CHCl₃ and CH/D₃CN have been identified by FTIR spectroscopy in the gas phase at room temperature. With increasing partial pressure of the components, The C-H stretching fundamental shifts to the blue which has been identified as due to C-H...N interaction. The C-H stretching frequency of CHCl₃ with CH₃CN and CD₃CN are shifted by +8.7 and +8.6 cm⁻¹,respectively. By using quantum chemical calculations at the MP2/6-311++G^** level, we predict the geometry, electronic structural parameters, binding energy, and spectral shift in the H-bonded complexes. The potential energy scans of the above complexes as a function of C...N distance shows that the H-bonding interaction is predominantly due to contribution of two opposing forces i.e.,electrostatic attraction between H and N which leads to the C-H bond elongation with consequent red-shift and the electronic and nuclear repulsion between the C and N which results in C-H bond contraction and blue-shift of the C-H stretching frequency. The net effect of these two opposing forces at the equilibrium complex geometry dictates the nature of the shift although the influence of the surrounding atoms bonded to the atoms that are directly involved in the H-bonding cannot be fully underestimated. The total interaction energy (-14.23 kJ/mol) is characterized by Morokuma energy decomposition analysis where the binding in CH/D₃CN ...CHCl₃ is dominated by electrostatic attraction (-25.86 kJ/mol). The attraction, however, is considerably suppressed by exchange repulsion (+19.54 kJ/mol). Other components like polarization (-5.44 kJ/mol) and charge transfer (-5.06 kJ/mol) make significant contribution to the interaction energy.

The two titled molecules have been studied in the past by one of us (RKB) and coworkers. Due to unassigned splittings of the methyl internal rotations, and inconsistencies in the spectroscopic fits the studies were deemed incomplete for a manuscript but were previously presented in isolation at ISMS in Columbus.Microwave study of 2-Methyl-Hexene-3-yne; Ground state and tortionally excited state; Yeager. Joseph, Bohn. Robert.K ISMS 2007Rotational spectrum and structure of 3-Hexyn-2-one; Bohn. Robert.K ISMS 1997y re-measurement we have identified new small splittings and added breadth the spectral fits to allow improved fitting. Parameters characterizing internal rotation have been determined for 2-methyl-1-hexen-3-yne for the first time. This work is part of a larger series of work which attempts to rationalize how molecules undergo structural and dynamical changes when altering one moiety, for example how an environment surrounding a double bond hinders the free rotation of an adjacent methyl group.

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Footnotes:

Microwave study of 2-Methyl-Hexene-3-yne; Ground state and tortionally excited state; Yeager. Joseph, Bohn. Robert.K ISMS 2007^, Rotational spectrum and structure of 3-Hexyn-2-one; Bohn. Robert.K ISMS 1997B

Cation-Helium complexes are interesting spectroscopic systems due to the floppy bond of the helium atom. He-HCO⁺ is a particularly interesting test system, as it is linear and has a ¹Σ ground state. So far experimental data have been limited to infrared studies on the ν₁ C-H stretching mode of He-HCO⁺. In order to obtain high-resolution rotational data the recently developed rotational-predissociation double resonance method has been applied to this complex. Accurate molecular parameters will be presented and discussed.

The ν₂ band of NH₃ and ND₃ in solid Ar at 8K inside an ice-film nanocapacitor is observed by reflection-absorption infrared spectroscopy (RAIRS). Ammonia is an almost-free rotor in the Ar matrix. As the electric field is increased up to 1x10⁶ V/cm, the spectrum undergoes a sequence of (reversible) changes driven by two kinds of Stark effect: mixing of inversion doublet components (for K_c ≥ 1) and c-dipole type ∆K=0, ∆J=±1 J-mixing. Mixing of inversion doublets results in quenching of the inversion dynamics and J-mixing leads toward pendularization. H vs. D nuclear permutation symmetry effects are clearly visible in the spectrum. At 10⁶ V/cm and 8 K, the Stark interaction energy, μE = 25 cm⁻¹, is larger than kBT = 5.6 cm⁻¹ and intermediate between the inversion splittings in the NH₃ v=0 and v₂=1 levels, 0.79 and 36.5 cm⁻¹. This frequency domain spectrum in a scanned DC electric field encodes a more complete dynamical picture than experiments in which an extremely high electric field is generated by a focused ultrafast laser pulse.

Samsung Science and Technology Foundation (SSTF-BA1301-04)

Superfluid helium nanodroplets present a unique environment for the investigation of the coupling of solvent density to the rotation of embedded molecules [1]. This coupling results in a reduction of the gas phase rotational constant, B_gas, by an amount that depends on both the gas phase rotational velocity and the anisotropy of the helium-rotor interaction potential [2]. We can gain insight into the dependence of B_gas on the coupling by investigating different isotopologues of a given molecule, such as HCN/DCN [3] (since the interaction potential is approximately the same between them). With this in mind, we recorded the high-resolution infrared spectra of carbonyl sulfide and methanol isotopologues from 4.7 to 5.0 μm, using a newly built spectrometer. This spectral region allows for coverage of the CO stretching and third overtone bending bands of carbonyl sulfide, and the symmetric CD₃ stretching band of methanol. For both systems, we find that the heavier isotopologues couple to more helium density, and explore the connection between the two molecules in terms of their dependence of B_gas on the amount of coupled helium density. [1] S. Grebenev, J. P. Toennies, and A. F. Vilesov, Science 279, 2083 (1998). [2] S. Paolini, S. Fantoni, S. Moroni, and S. Baroni, J. Chem. Phys. 123, 114306 (2005). [3] A. Conjusteau, C. Callegari, I. Reinhard, K. K. Lehmann, and G. Scoles, J. Chem. Phys. 113, 4840 (2000).

The temperature dependence of the vacuum ultraviolet charge transfer to solvent (CTTS) absorption spectra of aqueous halide and hydroxide ions was measured up to 300 ^°C in subcritical water. With increasing temperature, absorption spectra are observed to broaden and redshift, much in agreement with previous measurements below 100 ^°C. We discuss these changes alongside classic cavity models of the solvated species, where a gradual increase in cavity size is observed as a function of temperature while the Gibbs energy of hydration is largely unaffected. The changes in solvation properties are considered in the context of recent studies of the ultraviolet spectroscopy of subcritical water and historic studies of the CTTS absorption.