Philippe Lerch

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. The spectrometer is connected to the infrared port available at the Swiss Light Source (SLS) at the Paul-Scherrer-Institute (PSI). Due to the high brightness of the synchrotron radiation in the spectral region of interest, effectively up to 20 times brighter than thermal sources, and the high resolution of the new interferometer, it was possible to record the rotationally resolved infrared spectra of naphthalene and indole at room temperature, and to analyse the ν46 c-type band (ν̃(0) = 782.330949 cm(-1)) of naphthalene as well as the ν35 c-type band (ν̃(0) = 738.483592 cm(-1)) of indole and an a-type band at ν̃(0) = 790.864370 cm(-1) tentatively assigned as the overtone 2ν(40) of indole. The results of the naphthalene band analysis are discussed in relation to the Unidentified Infrared Band (UIB) found in interstellar spectra at 12.8 μm.

Amorphous mAteriAls: properties, structure, And durAbility† Compositional dependent compressibility of dissolved water in silicate glasses

Abstract The sound velocities and elastic properties of a series of hydrous rhyolite, andesite, and basalt glasses have been determined by Brillouin scattering spectroscopy at ambient conditions to elucidate the effect of glass composition on the compressibility of dissolved water. Both the adiabatic bulk (KS) and shear modulus (μ) of the dry glasses decrease with increasing silica content (KS,basalt > KS,andesite > KS,rhyolite and μbasalt > μandesite > μrhyolite). For each composition, the shear modulus systematically decreases with increasing water content. Although the addition of up to 14 mol% water decreases the KS of andesite and basalt glasses by up to 6%, there is no discernable effect of water on the KS of the rhyolite glasses. The partial molar KS of dissolved water (KS) in rhyolite, andesite, and basalt glasses are 37 ± 5, 19 ± 7, and 40 ± 3 GPa, corresponding to partial molar isothermal compressibilities (β̅T) of 0.029 ± 0.005, 0.042 ± 0.004, and 0.026 ± 0.002 GPa−1, respectively. These results indicate that the compressibility of dissolved water strongly depends on the bulk composition of the glass; hence, the partial molar volume of water cannot be independent of the bulk composition at elevated pressure. If the compressibility of dissolved water also depends on composition in the analog melts at high temperature and pressure, these observations will have important consequences for magmatic processes such as magma mixing/unmixing and fractional crystallization.

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.

Ultra-broadband infrared pump-probe spectroscopy using synchrotron radiation and a tuneable pump.

Synchrotron infrared sources have become popular mainly because of their excellent broadband brilliance, which enables spectroscopically resolved spatial-mapping of stationary objects at the diffraction limit. In this article we focus on an often-neglected further advantage of such sources - their unique time-structure - to bring such broadband spectroscopy to the time domain, for studying dynamic phenomenon down to the 100 ps limit. We describe the ultra-broadband (12.5 to 1.1 μm) Fourier transform pump-probe setup, for condensed matter transmission- and reflection-spectroscopy, installed at the X01DC infrared beam-line of the Swiss Light Source (SLS). The optical pump consists of a widely tuneable 100 ps 1 kHz laser system, covering 94% of the 16 to 1.1 μm range. A thorough description of the system is given, including (i) the vector-modulator providing purely electronic tuning of the pump-probe overlap up to 1 ms with sub-ps time resolution, (ii) the 500 MHz data acquisition system interfaced with the experimental physics and industrial control system (EPICS) based SLS control system for consecutive pulse sampling, and (iii) the step-scan time-slice Fourier transform scheme for simultaneous recording of the dual-channel pumped, un-pumped, and difference spectra. The typical signal/noise ratio of a single interferogram in a 100 ps time slice is 300 (measured during one single 140 s TopUp period). This signal/noise ratio is comparable to that of existing gated Globar pump-probe Fourier transform spectroscopy, but brings up to four orders of magnitude better time resolution. To showcase the utility of broadband pump-probe spectroscopy, we investigate a Ge-on-Si material system similar to that in which optically pumped direct-gap lasing was recently reported. We show that the mid-infrared reflection-spectra can be used to determine the optically injected carrier density, while the mid- and near-infrared transmission-spectra can be used to separate the strong pump-induced absorption and inversion processes present at the direct-gap energy.

Transient mid-IR study of electron dynamics in TiO2 conduction band

The dynamics of TiO2 conduction band electrons were followed with a novel broadband synchrotron-based transient mid-IR spectroscopy setup. The lifetime of conduction band electrons was found to be dependent on the injection method used. Direct band gap excitation results in a lifetime of 2.5 ns, whereas indirect excitation at 532 nm via Ru-N719 dye followed by injection from the dye into TiO2 results in a lifetime of 5.9 ns.

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 13.55 and 14.6 μm with biphenyl bands, but excluding azulene as a strong absorber.

Magnetic Determination of the Current Center Line for the Superconducting ITER TF Coils

The ITER tokamak includes 18 superconducting D-shaped toroidal field (TF) coils. Unavoidable shape deformations as well as assembly errors will lead to error fields in the final configuration, which can be modeled with the knowledge of the current center line (CCL). We are building a room temperature magnetic measurement system using low-frequency ac excitation current through the TF coil and arrays of pickup coils, fabricated with printed circuit board technology. Deviations from the expected shape of the CCL will be obtained by comparing the amplitude of magnetic flux measured at several locations around the perimeter of the TF coil, with values computed assuming the nominal current distribution. We present experimental results obtained with a cable placed in one-turn groove of a full scale radial plate.

Room Temperature Magnetic Determination of the Current Center Line for the ITER TF Coils

The ITER tokamak includes 18 superconducting D-shaped toroidal field (TF) coils. Unavoidable shape deformations as well as assembly errors will lead to field errors, which can be modeled with the knowledge of the current center line (CCL). Accurate survey during the entire manufacturing and assembly process, including transfer of survey points, is complex. In order to increase the level of confidence, a room temperature magnetic measurement of the CCL on assembled and closed winding packs is foreseen, prior to insertion into their cold case. In this contribution, we discuss the principle of the CCL determination and present a low frequency ac measurement system under development at PSI, within an ITER framework contract. The largest current allowed to flow in the TF coil at room temperature and the precision requirements for the determination of the CCL loci of the coil are hard boundaries. Eddy currents in the radial plates, the winding pack enclosures, and possibly from iron in the reinforced concrete floor of the assembly hall are more subtle to bring under control quantitatively, and will limit the highest frequency that can be used to measure reliable values of the field gradients. Our objective is to measure the CCL loci by combining magnetic data obtained with printed circuit board flux coils and survey data gathered around the perimeter of the D-shaped coil.

A combined Gigahertz and Terahertz (FTIR) spectroscopic investigation of meta-D-phenol: observation of tunnelling switching

ABSTRACT We report results on the dynamics of tunnelling switching based on a high-resolution spectroscopic investigation of meta-D-phenol in GHz and THz ranges. The pure rotational spectra were recorded in the range of 72–117 GHz and assigned to the localized syn- and anti-structures in the ground and the first excited torsional states. Specific torsional states were unambiguously assigned by comparison of the experimental rotational constants with theoretical results from quasiadiabatic channel reaction path Hamiltonian (RPH) calculations. The torsional fundamental νT at ≈ 309 cm−1 and the first hot band (2νT – νT) at ≈ 277 cm−1 were subsequently assigned in synchrotron based high-resolution Fourier transform infrared (FTIR, THz) spectra. The analyses provided accurate spectroscopic constants of all six states involved. It was found that the 2νT states are interacting through anharmonic resonances, indicating tunnelling switching as predicted by theory. Furthermore, tunnelling–rotation–vibration transitions were assigned and the tunnelling splitting in 2νT was determined as 1.72450(17) cm−1. This key result allowed the assignment of two Q branches at 275.21303(9) and 277.67127(9) cm−1 to vibration-tunnelling transitions of the (syn ← anti) type, hence confirming tunnelling switching dynamics in m-D-phenol. The ground-state energy difference of the syn- and anti-isotopomers is obtained experimentally as E0 (syn) - E0 (anti) = (hc)0.82 cm−1 in satisfactory agreement with the theoretical ab initio predictions of (hc)1.5 cm−1 given the small absolute values arising from the tiny zero point energy effects. The results are discussed in relation to further fundamental aspects of tunnelling in slightly asymmetric potentials including the effects of the parity violating electroweak interaction in chiral molecules.

submitter : Magnetic Determination of the Current Center Line for the Superconducting ITER Toroidal Field Coils: Results on a Double-Pancake Prototype

In the context of the ITER project, the winding geometry of the large-scale magnetic field coils has to be validated. A geometrical survey during manufacturing is combined with a magnetic survey of finished assemblies. We are developing a fluxmeter system, which is capable of sampling magnetic flux density values (or gradients thereof) at many locations distributed around the assembly. The measurement method uses low-frequency (300 mHz-1.2 Hz) ac excitation of the coil under study and acquires induced voltage values sensed by magnetic flux pickup coils. The sampling strategy leverages on the use of calibrated arrays of coils mounted on rigid supports. The supports, whose positions in space are measured with a laser tracker, carry 48 distinct coils and are placed at several locations around the perimeter of the magnet under study. Maps of induced voltage values, corresponding to time-varying magnetic flux, are recorded. In this contribution, we present experimental results obtained on the first available European double-pancake prototype (12 turns) for the toroidal field coils and compare the results with feedforward computation using magnetostatics. At 300 mHz, the global relative agreement between measured and computed signal amplitude is in the % range. It is necessary to take into account the knowledge of the actual shape of the 12-turn current filament.