Communication: Molecular gears.

The (1)H nuclear magnetic resonance spectrum of hexamethylbenzene orientationally ordered in the nematic liquid crystal ZLI-1132 is analysed using covariance matrix adaptation evolution strategy. The spectrum contains over 350 000 lines with many overlapping transitions, from which four independent direct dipolar couplings are obtained. The rotations of the six methyl groups appear to be correlated due to mutual steric hindrance.

Communication: molecular dynamics and (1)H NMR of n-hexane in liquid crystals.

The NMR spectrum of n-hexane orientationally ordered in the nematic liquid crystal ZLI-1132 is analysed using covariance matrix adaptation evolution strategy (CMA-ES). The spectrum contains over 150 000 transitions, with many sharp features appearing above a broad, underlying background signal that results from the plethora of overlapping transitions from the n-hexane as well as from the liquid crystal. The CMA-ES requires initial search ranges for NMR spectral parameters, notably the direct dipolar couplings.

A model-free temperature-dependent conformational study of n-pentane in nematic liquid crystals.

The proton NMR spectra of n-pentane orientationally ordered in two nematic liquid-crystal solvents are studied over a wide temperature range and analysed using covariance matrix adaptation evolutionary strategy. Since alkanes possess small electrostatic moments, their anisotropic intermolecular interactions are dominated by short-range size-and-shape effects. As we assumed for n-butane, the anisotropic energy parameters of each n-pentane conformer are taken to be proportional to those of ethane and propane, independent of temperature.

Efficient analysis of highly complex nuclear magnetic resonance spectra of flexible solutes in ordered liquids by using molecular dynamics.

The NMR spectra of n-pentane as solute in the liquid crystal 5CB are measured at several temperatures in the nematic phase. Atomistic molecular dynamics simulations of this system are carried out to predict the dipolar couplings of the orientationally ordered pentane, and the spectra predicted from these simulations are compared with the NMR experimental ones. The simulation predictions provide an excellent starting point for analysis of the experimental NMR spectra using the covariance matrix adaptation evolutionary strategy.

Nuclear magnetic resonance study of alkane conformational statistics.

NMR spectra of ethane, propane, and n-butane as solutes in the nematic liquid crystals 4-n-pentyl-4(')-cyanobiphenyl (5CB) and Merck ZLI 1132 (1132) are investigated over a wide temperature range. The ratios of dipolar couplings of ethane to propane are constant over the entire temperature range. Assuming that this constancy applies to the butane conformers facilitates the separation of probability from order parameter.

Spectral identification of diffuse resonances in H2 above the n = 2 dissociation limit.

The resonance structure in molecular hydrogen above the n = 2 dissociation limit is experimentally investigated in a 1 XUV + 1 VIS coherent two-step laser excitation process, with subsequent ionization of H(n = 2) products. Diffuse spectral features exhibiting widths of several cm(-1) in the excitation range of 118,500-120,500 cm(-1) are probed. Information on angular momentum selection rules for parallel and crossed polarizations, combination differences, the para-ortho distinction, extrapolation from rovibrational structure in the bound region below the n = 2 threshold, and mass-selective detection of H(2)(+) parent and H(+) daughter fragments is used as input.

Scope and limitations of accurate structure determination of solutes dissolved in liquid crystals.

The determination of accurate structures of relatively small molecules dissolved in liquid-crystal solvents is no trivial matter. Extensive vibrational corrections to the observed dipolar couplings are required. Vibrational force fields are often available, but the usual harmonic corrections are strictly limited to small-amplitude internal motions.

Spectroscopic observation and characterization of H(+)H(-) heavy Rydberg states.

A series of discrete resonances was observed in the spectrum of H2, which can be unambiguously assigned to bound quantum states in the 1/R Coulombic potential of the H+H- ion-pair system. Two-step laser excitation was performed, using tunable extreme ultraviolet radiation at lambda = 94-96 nm in the first step, and tunable ultraviolet radiation in the range lambda = 310-350 nm in the second step. The resonances, detected via H+ and H2+ ions produced in the decay process, follow a sequence of principal quantum numbers (n = 140-230) associated with a Rydberg formula in which the Rydberg constant is mass scaled.

Evolutionary algorithms to solve complicated NMR spectra.

The complexity of (1)H NMR spectra of solutes in partially ordered solvents such as liquid crystals increases rapidly with the number of spins. Spectra of simple solutes with sufficient symmetry and containing not too many spins (typically View Article and Find Full Text PDF

Observation of a Rydberg series in H+H-: a heavy Bohr atom.

We report on the realization of a heavy "Bohr atom," through the spectroscopic observation of a Rydberg series of bound quantum states at principal quantum numbers n=140 to 230. The system is made heavy by replacing an electron inside a hydrogen atom by a composite H- particle, thus forming a H+H- Coulombically bound system obeying the physical laws of a generalized atom with appropriate mass scaling.

Interactions of the 3ppi u c1Pi u(v=2) Rydberg-complex member in isotopic N2.

The 3ppi u c1Pi u-X 1Sigmag+(2,0) Rydberg and b' 1Sigmau+-X 1Sigmag+(7,0) valence transitions of 14N2, 14N15N, and 15N2 are studied using laser-based 1 extreme ultraviolet (XUV)+1' UV two-photon-ionization spectroscopy, supplemented by synchrotron-based hotoabsorption measurements in the case of 14N2. For each isotopomer, effective rotational interactions between the c(v=2) and b'(v=7) levels are found to cause strong Lambda-doubling in c(v=2) and dramatic P/R-branch intensity anomalies in the b'-X(7,0) band due to the effects of quantum interference. Local perturbations in energy and predissociation line width for the c(v=2) Rydberg level are observed and attributed to a spin-orbit interaction with the crossing, short-lived C 3Pi u(v=17) valence level.

HD as a probe for detecting mass variation on a cosmological time scale.

The strong electronic absorption systems of the B1 Sigma u+-X1 Sigma g+ Lyman and the C1Pi u-X1 Sigma g+ Werner bands can be used to probe possible mass-variation effects on a cosmological time scale from spectra observed at high redshift, not only in H2 but also in the second most abundant hydrogen isotopomer HD. High resolution laboratory determination of the most prominent HD lines at extreme ultraviolet wavelengths is performed at an accuracy of delta lambda/lambda approximately 5 x 10(-8), forming a database for comparison with astrophysical data. Sensitivity coefficients Ki = d ln lambda i/d ln mu are determined for HD from quantum ab initio calculations as a function of the proton-electron mass ratio mu.

Molecules with large-amplitude torsional motion partially oriented in a nematic liquid crystal: ethane and isotopomers.

An NMR study on ethane and five isotopomers dissolved in the nematic liquid crystal Merck ZLI 1132 is performed. A consistent set of dipolar and quadrupolar couplings is obtained. The dipolar couplings are corrected for harmonic vibrational effects, while the contribution from the torsional motion is incorporated classically.

NMR as a tool in the investigation of fundamental problems in ordered liquids.

An overview is presented of modern NMR techniques and a variety of experimental and theoretical tools employed in the study of solutes dissolved in liquid crystals. The NMR techniques involve multiple quantum and spectral subtraction methods. In addition, various experimental and theoretical tools are discussed, including: the theoretical background of observed order parameters; the use of 'magic mixtures' to separate orientational contributions; the reorientation-vibration interaction; the use of model calculations based on size and shape of the various solutes; and the use of computer simulations.

Absolute ionization rates of multielectron transition metal atoms in strong infrared laser fields.

We report on nonresonant strong field ionization of the multielectron transition metal atoms V, Nb, Ta, Ni, and Pd. Operating in the adiabatic regime (lambda = 1.5 microm), we quantitatively determined both (i) the first charge state saturation intensities and (ii) the absolute ionization rates for intensities ranging from threshold up to 3 x 10(14) W/cm2.

Dynamic polarization in the strong-field ionization of small metal clusters.

We report on the strong field ionization of small transition metal clusters (nickel, Ni(n) n=1-36) within the quasistatic regime at an infrared wavelength of 1.5 microm and at intensities up to 2 x 10(14) W/cm(2). From ion yields in a constant axial intensity beam, we obtained saturation intensities for the individual Ni(n) clusters.

Resonance-enhanced multiphoton ionisation photoelectron spectroscopy of the ClO radical: the C 2 sigma- state.

A (2 + 1) one-colour resonance-enhanced multiphoton ionisation study is carried out on the C 2 sigma- state of the ClO radical in the one-photon energy range 29,500-31,250 cm-1. The ClO radical is produced by one-photon photolysis of ClO2 employing 359.2 nm photons derived from a separate laser.

CARS microscopy with folded BoxCARS phasematching.

Three-dimensional microscopy based on coherent anti-Stokes Raman scattering (CARS) is a powerful new imaging technique, in which the contrast arises from molecular vibrations. Based on a simple numerical model, it is shown how the CARS interaction volume depends on the focusing parameters and the type of phasematching used. Collinear phasematching yields an ellipsoidal interaction volume, with lateral dimensions that readily cause vignetting of the CARS signal emission at the collection microscope objective.