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.

High resolution ro-vibrational analysis of molecules in doublet electronic states: the fundamental of chlorine dioxide (OClO) in the 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.

Nuclear Spin Symmetry Conservation Studied for Symmetric Top Molecules (CHD, CHD, CHF, and CHCl) in Supersonic Jet Expansions.

We report results on nuclear spin symmetry conservation studied by high resolution spectroscopy of relative line intensities for the A and E nuclear spin isomers of symmetric top molecules CHD, CHD, CHF, and CHCl in supersonic jet expansions with He and Ar as carrier gases. Infrared absorption spectra were measured around 3000 cm by an infrared (lead salt) diode laser and a continuous wave IR-OPO (infrared optical parametric oscillator) locked to a frequency comb. A detailed analysis of the R(2)-line intensities of the CH-stretching fundamental shows that nuclear spin symmetry is conserved for CHD, CHF, and CHCl during the expansion.

Controlling tunneling in ammonia isotopomers.

We report results of full-dimensional variational rovibrational quantum-dynamical computations for several ammonia isotopomers, based on selected potential energy and electric dipole moment hypersurfaces. The variational rovibrational eigenstates have been used as a basis for the solution of the time-dependent Schrödinger equation for nuclear motion including coherent infrared multiphoton excitation. The theoretical and computational framework developed during this study enables the investigation of the coherent inhibition or enhancement of tunneling in ammonia isotopomers by appropriately chosen laser fields.

The Gigahertz and Terahertz spectrum of monodeutero-oxirane (c-CHDO).

The rotational spectrum of monodeutero-oxirane was analysed as measured using the Zurich Gigahertz (GHz) spectrometer and our highest resolution Fourier Transform Infrared (FTIR) spectrometer system coupled to synchrotron radiation at the Swiss Light Source (SLS). 112 distinct line frequencies have been newly assigned in the GHz range (extended to 120 GHz, compared to previous work extending to only 59 GHz) including rotational states up to J = 23. We have furthermore assigned 398 lines in the far infrared or Terahertz range (0.

Intramolecular vibrational energy redistribution in HCCCHX (X = Cl, Br, I) measured by femtosecond pump-probe experiments in a hollow waveguide.

From the analysis of high resolution overtone spectra it is well established that intramolecular vibrational energy redistribution (IVR) from an initially excited CH-stretching vibration is strongly influenced by its chemical environment. Due to a pronounced Fermi resonance between the CH-stretching and CH-bending vibrations a vibrational energy redistribution on the subpicosecond time scale (∼100 fs) is found for alkyl (sp3) CH-chromophores, whereas this doorway for energy flow is blocked for the acetylenic (sp) CH-stretching vibration because of the much lower CH-bending frequency. From the analysis of the high resolution spectra lifetimes for the initial CH-vibrational excitation of 10-100 ps or longer have been derived.

A molecular quantum switch based on tunneling in meta-d-phenol CHDOH.

We introduce the concept of a molecular quantum switch and demonstrate it with the example of meta-d-phenol, based on recent theoretical and high-resolution spectroscopic results for this molecule. We show that in the regime of tunneling switching with localized low-energy states and delocalized high-energy states the molecular quantum switch can be operated in two different ways: (i) a quasiclassical switching by coherent infrared radiation between the two isomeric structures syn- and anti-m-d-phenol; and (ii) a highly nonclassical switching making use of bistructural quantum superposition states of the syn and anti structures, which can be observed by their time-dependent spectra after preparation.

On the use of nonrigid-molecular symmetry in nuclear motion computations employing a discrete variable representation: A case study of the bending energy levels of CH.

A discrete-variable-representation-based symmetry adaptation algorithm is presented and implemented in the fourth-age quantum-chemical rotational-vibrational code GENIUSH. The utility of the symmetry-adapted version of GENIUSH is demonstrated by the computation of seven-dimensional bend-only vibrational and rovibrational eigenstates of the highly fluxionally symmetric CH molecular ion, a prototypical astructural system. While the numerical results obtained and the symmetry labels of the computed rovibrational states of CH are of considerable utility by themselves, it must also be noted that the present study confirms that the nearly unconstrained motion of the five hydrogen atoms orbiting around the central carbon atom results in highly complex rotational-vibrational quantum dynamics and renders the understanding of the high-resolution spectra of CH extremely challenging.

Isotope effects on the resonance interactions and vibrational quantum dynamics of fluoroform CHF.

We report a comparison of the analysis of the low energy spectrum of CHF and CHF from the THz (FIR) range to the ν fundamental at high resolution (δ[small nu, Greek, tilde] < 0.001 cm or otherwise Doppler limited) on the basis of FTIR spectra taken both with ordinary light sources and with the synchrotron radiation from the Swiss Light Source. Several vibrational levels are accurately determined including, in particular, the 2ν CH-bending overtone and the ν CH-stretching fundamental of CHF.

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

The chiral C symmetric molecule 1,2-dithiine (1,2-dithia-3,5-hexadiene, CHS) 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 ν using highest resolution synchrotron-based interferometric Fourier transform infrared (FTIR) spectroscopy in the terahertz range with a band center of ν = 6.95375559 THz (ν̃ = 231.

Wavepacket Dynamics of the Axially Chiral Molecule Cl-O-O-Cl under Coherent Radiative Excitation and Including Electroweak Parity Violation.

We report detailed calculations of the quantum wavepacket dynamics of Cl-O-O-Cl, which serves as a prototype molecule for the stereomutation dynamics of an axially chiral molecule. We include the effects both from electroweak parity violation and from the interaction with a coherent monochromatic laser field. We use the quasiadiabatic channel reaction path Hamiltonian approach to approximately solve the six-dimensional Schrödinger equation describing the vibrational motion, including rotation by an effective Hamiltonian.

Tunneling and Parity Violation in Trisulfane (HSSSH): An Almost Ideal Molecule for Detecting Parity Violation in Chiral Molecules.

Measuring the parity-violating energy difference Δpv E between the enantiomers of chiral molecules is a major challenge of current physical-chemical stereochemistry. An important step towards this goal is to identify suitable molecules for such experiments by means of theory. This step has been made by calculations for the complex dynamics of tunneling and electroweak quantum chemistry of parity violation in the "classic" molecule trisulfane, HSSSH, which satisfies the relevant conditions for experiments almost ideally, as the molecule is comparatively simple and parity violation clearly dominates over tunneling in the ground state.

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.

Synchrotron-based rotationally resolved high-resolution FTIR spectroscopy of azulene and the unidentified infrared bands of astronomy.

Chasing the unidentified IR bands: The first rotationally resolved high-resolution infrared spectrum of azulene is reported using synchrotron Fourier transform infrared spectroscopy including a rovibrational analysis of the out-of-plane fundamental ν44. Comparison of azulene, naphthalene, indole, and biphenyl infrared bands leads to coincidences with UIR bands at 12.8 μm with naphthalene and at 13.

Global analytical potential energy surface for the electronic ground state of NH3 from high level ab initio calculations.

The analytical, full-dimensional, and global representation of the potential energy surface of NH(3) in the lowest adiabatic electronic state developed previously (Marquardt, R.; et al. J.

Nuclear spin symmetry conservation and relaxation in water ((1)H2(16)O) studied by cavity ring-down (CRD) spectroscopy of supersonic jets.

We report high resolution near-infrared laser spectra of water seeded in a supersonic jet expansion of argon probed by cavity ring-down spectroscopy (CRDS) in the R branch of the 2ν3 band (above 7500 cm(-1)) at several effective temperatures T < 30 K. Our goal is to study nuclear spin symmetry conservation and relaxation. For low mole fractions of water in the gas mixture, we obtained the lowest rotational temperatures and observed nuclear spin symmetry conservation, in agreement with theoretical expectation for inelastic collisions of isolated H2O molecules with Ar and similar to a previous series of experiments with other small molecules in supersonic jet expansions.

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.

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.

Synchrotron-based highest resolution Fourier Transform infrared spectroscopy of naphthalene (C10H8) and indole (C8H7N) and its application to astrophysical problems.

We report a rotationally resolved analysis of the high resolution FTIR spectrum of naphthalene which can be considered as a prototypical molecule for polycyclic aromatic hydrocarbons (PAHs), and a similar analysis for the prototypical heterocyclic aromatic molecule indole. The spectra have been measured using a resolution of 0.0008 cm(-1) (21 MHz) with the new high resolution FTIR prototype spectrometer of the Molecular Kinetics and Spectroscopy Group at ETH Zürich.

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.

High-resolution continuous-wave-diode laser cavity ring-down spectroscopy of the hydrogen fluoride dimer in a pulsed slit jet expansion: two components of the N=2 triad near 1.3 microm.

The near-infrared overtone spectra of the prototypical hydrogen-bond hydrogen fluoride dimer (HF)2 contain rich information on hydrogen bond dynamics. We report a study of the N=2 triad involving excitations with two quanta of HF stretching in (HF)2 around 1.3 microm (7500-7800 cm(-1)) by means of continuous-wave-diode laser cavity ring-down spectroscopy in a pulsed supersonic slit jet expansion.

Spectroscopic properties of trichlorofluoromethane CCl(3)F calculated by density functional theory.

Density functional theory is used to generate local potential energy surfaces in normal coordinates for several chlorine isotopomers of trichlorofluoromethane (CCl(3)F, CFC11). An examination of predicted structures suggested that the PBE0 functional would be suitable. Anharmonic surfaces around the equilibrium geometries are reported, as determined by energies, gradients, and second derivatives.

High resolution rovibrational spectroscopy of chiral and aromatic compounds.

The analysis of selected rovibrationally resolved infrared spectra of some relatively heavy and large polyatomic molecules is reviewed. A short historical summary of the development of high resolution interferometric Fourier transform infrared (FTIR) spectrometers is given and the possibilities of the currently most highly resolving FTIR spectrometer, which is commercially available in the Bruker IFS 125 series, are discussed. The computational tools necessary to analyse FTIR spectra are described briefly.