Stereomutation Tunneling Switching Dynamics and Parity Violation in Chlorineperoxide Cl−O−O−Cl

High resolution spectroscopy of the ν1+ν3 band of the 35ClO2 free radical: Spin-rotation-vibration interactions

The high resolution spectrum of the ν₁+ν₃ band of the ³⁵ClO₂ free radical was recorded with a Bruker IFS 125HR Fourier transform infrared spectrometer and theoretically analysed with an improved theoretical basis including the reduced effective spin-rotation Hamiltonian (which takes into account sixth order operators describing spin-rotational interactions) and a newly created computer code ROVDES for the ro-vibrational spectra of open-shell free radicals. About 2600 spin-ro-vibrational transitions with the values N^max=59 and K_a^max=17 (being about 2.4 times higher in comparison with the number of assigned transitions known in the literature) were assigned to the ν₁+ν₃ band of ³⁵ClO₂ and 1049 spin-ro-vibrational energies (produced only from unblended non-saturated and not very weak experimental lines) of the (101) upper vibrational state were obtained. A set of 30 varied parameters of the effective spin-rotation-vibration Hamiltonian of the (101) vibrational state (vibrational energy, 17 rotational and centrifugal distortion parameters and 12 are spin-rotational ones) was determined from the weighted fit of parameters of the effective spin-rotational Hamiltonian in A-reduction and I^r-representation. The obtained set of parameters reproduces the initial 1049 "experimental" upper state energies with the d_rms=2.5×10^-4 cm^-1 which is close to the experimental uncertainty of the recorded spectra and is almost 70 times higher in comparison with the analogous reproduction of the same initial upper energies with the use of parameters from (J.Mol.Spectrosc.,158,347-356(1993)).

Perspectives on parity violation in chiral molecules: theory, spectroscopic experiment and biomolecular homochirality

The reflection (or ‘mirror’) symmetry of space is among the fundamental symmetries of physics. It is connected to the conservation law for the quantum number parity and a fundamental ‘non-observable’ property of space (as defined by an absolute ‘left-handed’ or ‘right-handed’ coordinate system). The discovery of the violation of this symmetry – the non-conservation of parity or ‘parity violation’ – in 1956/1957 had an important influence on the further development of physics. In chemistry the mirror symmetry of space is connected to the existence of enantiomers as isomers of chiral (‘handed’) molecules. These isomers would relate to each other as idealized left or right hand or as image and mirror image and would be energetically exactly equivalent with perfect space inversion symmetry. Parity violation results in an extremely small ‘parity violating’ energy difference between the ground states of the enantiomers which can be theoretically calculated to be about 100 aeV to 1 feV (equivalent to 10⁻¹¹ to 10⁻¹⁰ J mol⁻¹), depending on the molecule, but which has not yet been detected experimentally. Its detection remains one of the great challenges of current physical–chemical stereochemistry, with implications also for fundamental problems in physics. In biochemistry and molecular biology one finds a related fundamental question unanswered for more than 100 years: the evolution of ‘homochirality’, which is the practically exclusive preference of one chiral, enantiomeric form as building blocks in the biopolymers of all known forms of life (the l-amino acids in proteins and d-sugars in DNA, not the reverse d-amino acids or l-sugars). In astrobiology the spectroscopic detection of homochirality could be used as strong evidence for the existence of extraterrestrial life, if any. After a brief conceptual and historical introduction we review the development, current status, and progress along these three lines of research: theory, spectroscopic experiment and the outlook towards an understanding of the evolution of biomolecular homochirality.

The reflection (or ‘mirror’) symmetry of space is among the fundamental symmetries of physics. It is connected to the conservation law for the quantum number purity and its violation and has a fundamental relation to stereochemistry and molecular chirality.

High resolution ro-vibrational analysis of molecules in doublet electronic states: the ν1 fundamental of chlorine dioxide (16O35Cl16O) in the X2B1 electronic ground state

We report the spectrum of the ν1 fundamental of chlorine dioxide centered in the infrared atmospheric window at 945.592 cm-1 measured with essentially Doppler limited resolution at an instrumental line width of 0.001 cm-1 using the Zürich prototype ZP2001 Bruker IFS 125 HR Fourier transform infrared spectrometer. The ro-vibrational line analysis is carried out with an improved effective Hamiltonian and a newly developed computer code ROVDES for the ro-vibrational spectra of open-shell free radical molecules including spin-rotation interactions. Accurate values of rotational, centrifugal and spin-rotational parameters were determined for 16O35Cl16O in the vibronic ground state X2B1 from more than 3500 ground state combination differences. The 7239 assigned transitions for the ν1 fundamental with Nmax = 76 and Kmaxa = 26 provide a set of 32 accurate effective Hamiltonian parameters for the ν1 fundamental (v1v2v3) = (100) (21 rotational and centrifugal distortion parameters and 11 spin-rotational interaction parameters). This effective Hamiltonian (A - reduction and Ir - representation) reproduces 1703 upper state energies from the experiment with a root-mean-square deviation drms = 1.67 × 10-4 cm-1 and the 7239 transition wavenumbers with drms = 3.45 × 10-4 cm-1. Our results provide a considerable improvement over previous results with which we compare and should provide a benchmark for theoretical studies with applications to atmospheric spectroscopy and laser chemistry, which are discussed in relation to our spectra.

Dichlorine peroxide (ClOOCl), chloryl chloride (ClCl(O)O) and chlorine chlorite (ClOClO): very accurateab initiostructures and actinic degradation

The structural parameters of the three most stable isomers with formula Cl₂O₂, dichlorine peroxide, chloryl chloride and chlorine chlorite, were determined by high-levelab initiotheory. The photodissociation pathways were investigated.

Synchrotron-Based Highest Resolution Terahertz Spectroscopy of the ν24 Band System of 1,2-Dithiine (C4H4S2): A Candidate for Measuring the Parity Violating Energy Difference between Enantiomers of Chiral Molecules

The chiral C₂ symmetric molecule 1,2-dithiine (1,2-dithia-3,5-hexadiene, C₄H₄S₂) has been identified as a possible candidate for measuring the parity violating energy difference between enantiomers. We report here the observation and analysis of the low-frequency fundamental ν₂₄ using highest resolution synchrotron-based interferometric Fourier transform infrared (FTIR) spectroscopy in the terahertz range with a band center of ν₀ = 6.95375559 THz (ν̃₀ = 231.952319 (10) cm^-1) and two related hot bands, the (ν₁₃ + ν₂₄) ← ν₁₃ band at ν₀ = 6.97256882 THz (ν̃₀ = 232.579861 (33) cm^-1) and the 2ν₂₄ ← ν₂₄ band at ν₀ = 7.01400434 THz (ν̃₀ = 233.962001 (14) cm^-1). This success in the difficult analyses of the THz spectrum of a complex chiral molecule of importance for fundamental tests on molecular parity violation is enabled by the ideal setup of an FTIR experiment of currently unique resolution with the very stable and bright synchrotron radiation at the Swiss Light Source (SLS).

High resolution GHz and THz (FTIR) spectroscopy and theory of parity violation and tunneling for 1,2-dithiine (C4H4S2) as a candidate for measuring the parity violating energy difference between enantiomers of chiral molecules

Our results show that this molecule is a suitable candidate for a possible first determination of the parity violating energy difference Δ_pvE between enantiomers.

Line shape of amplitude or frequency-modulated spectral profiles including resonator distortions

We report experiments and an improved method of analysis for any harmonics of frequency-modulated spectral line shapes allowing for very precise determinations of the resonance frequency of single absorption lines for gigahertz spectroscopy in the gas phase. Resonator perturbations are implemented into the formalism of modulation spectroscopy by means of a full complex transmission function being able to model the asymmetrically distorted absorption line shapes for arbitrary modulation depths, modulation frequencies, and resonator reflectivities. Exact equations of the in-phase and the quadrature modulation signal, taking into account a full resonator transmission function, are simultaneously adjusted to two-channel lock-in measurements performed in the gigahertz regime to obtain the spectral line position. The determination of the absorption line position of the rotational transition J' = 7 ← J" = 6 of (16)O(12)C(32)S in the vibrational ground state is investigated while changing the resonator distortions. The results are subjected to the approach proposed here and compared to standard methods known from the literature.

Tunneling and tunneling switching dynamics in phenol and its isotopomers from high-resolution FTIR spectroscopy with synchrotron radiation

Tunneling and chemical reactions by tunneling switching are reported for phenol and ortho-deuterophenol on the basis of high-resolution FTIR spectroscopy. Tunneling splittings are measured for the torsional motion in the ground and several vibrationally excited states of phenol. Tunneling times range from 10 ns to 1 ps, depending on excitation. For more-highly excited torsional levels in ortho-deuterophenol, delocalization and chemical reaction by tunneling switching is found.

Frontiers in spectroscopy

We review the frontiers of spectroscopy from a historical perspective, starting with the development of atomic spectroscopy about 150 years ago, followed by some comments on selected previous Faraday Discussions. As the spectrum of frontiers at the Faraday Discussion 150 is very broad, we give only a brief survey providing a map of the various frontiers approached today. This is followed by an exemplary discussion of one particular frontier towards the spectroscopic detection of symmetry violations in fundamental physics. In particular the understanding of parity violation in chiral molecules has recently made great progress. We briefly describe the advances made in recent decades as well as the current status of theory and experiments in this exciting field of research. We conclude with an outlook on open questions and frontiers of the future in spectroscopy.

Chiral oxorhenium(V) complexes as candidates for the experimental observation of molecular parity violation: a structural, synthetic and theoretical study

We report the synthesis and resolution of a series of new chiral "3 + 1" oxorhenium(V) complexes, designed for high-resolution laser spectroscopy experiments probing molecular parity-violation (PV) effects in the Re=O stretching mode frequency. These complexes display a particularly simple chemical structure, with the rhenium atom as the stereogenic center, and show large PV energy differences according to our calculations. They were obtained in the racemic and enantioenriched forms, in the latter case by using either semi-preparative chiral HPLC resolution or enantioselective synthesis. The vibrational transition frequency differences between the enantiomeric pairs due to PV have been calculated with two- and four-component relativistic Hamiltonians using Hartree-Fock (HF) and density functional theory (DFT). For three complexes, including one synthesized in enantioenriched form, our HF calculations predict frequency differences above the present resolution limit of 1 Hz. These results confirm the order of magnitude for the calculated HF PV vibrational frequency differences reported earlier for this class of compounds [P. Schwerdtfeger and R. Bast, J. Am. Chem. Soc., 2004, 126, 1652]. However, at the DFT level the PV vibrational frequency differences are in some cases reduced by an order of magnitude, but are still within the sensitivity of 0.01 Hz, which is the anticipated sensitivity in a new proposed experiment. We therefore believe that the present study represents an important step towards the experimental observation of PV in molecular systems, and emphasizes the extreme sensitivity of the PV vibrational frequency difference to the chemical environment around the rhenium center.

High-Resolution Spectroscopic Studies and Theory of Parity Violation in Chiral Molecules

We review the high-resolution spectroscopic approach toward the study of intramolecular dynamics, emphasizing molecular parity violation. Theoretical work in the past decade has shown that parity-violating potentials in chiral molecules are much larger (typically one to two orders of magnitude) than anticipated on the basis of older theories. This makes experimental approaches toward small molecular parity-violating effects promising. The concepts and results of intramolecular dynamics derived from spectroscopy are analyzed as a sequence of symmetry breakings. We summarize the concepts of symmetry breakings (de facto and de lege) in view of parity violation in chiral molecules. The experimental schemes and the current status of spectroscopic experiments on molecular parity violation are established. We discuss the promises of detecting and accurately measuring parity-violating energy differences Δpv E on the order of 10−11 J mol−1 (approximately 100 aeV) in enantiomers of chiral molecules with regard to their contribution to fundamental physics in the framework of the standard model of particle physics and more speculative future fundamental symmetry tests such as for the combined charge conjugation, parity, and time-reversal (CPT) symmetry violation.