Molecules' Rotation Signals (and Their Observation): Torsion, Inversion, Flexibility, Chirality, Phase

All molecular system come with their own set of challenges for rotational spectroscopy, theoretically and experimentally: (Multiple) internal interactions might cause complicated energy level schemes and the resulting spectra will be rather difficult to predict theoretically. Experimentally, these spectra are difficult to assess and assign. With today’s broad-band microwave (MW) techniques, finding and identifying such spectral features have lost their major drawback of being very time consuming for many molecules. The unrivalled resolution of advanced fast-passage spectrometers, previously only available for narrow-banded MW techniques, now also allows to tackle - at the highest precision – very subtle effects. Historically, (very) low barriers to large amplitude motions leading to (very) large tunnelling splittings often prevented an experimental assessment or, if identified, their analysis to experimental accuracy. Barriers to large amplitude motions can not only be related to the local atom arrangement but also to the molecular orbital and electron density structure, e.g. chemical information relayed through conjugated $\pi$-systems, of the molecule. Theoretically, such systems require calculations at elevated levels, e.g. CCSD(T)/cc-pcVTZ or beyond, but quantitative predictions of the dynamical features often still fall behind those of equilibrium structures. Experimentally, the analysis might require the measurement of tunneling species (in the cm- and mm-wave regions) beyond the torsional ground state to reveal the origin of the observed spectrum and underlying hindering potential. Furthermore - in the realm of barriers to large amplitude motions - details on internal dynamics and the (stereo-chemical) molecular structure encode their nature in the coherent signature of molecular rotation spectra obtained after single- and/or double-resonance excitation. Phase, indeed, provides pitfalls here and elsewhere. Current examples and new directions together with an outlook will be given

Precise dipole moment and quadrupole coupling constants of benzonitrile

We have performed Fourier transform microwave spectroscopy of benzonitrile, without and with applied electric fields. From the field-free hyperfine-resolved microwave transitions we simultaneously derive accurate values for the rotational constants, centrifugal distortion constants, and nitrogen nuclear quadrupole coupling constants of benzonitrile. By measuring the Stark shift of selected hyperfine transitions the electric dipole moment of benzonitrile is determined to $\mu=\mu_a=4.5152 (68)$ D.Comment: 6 pages, 2 tables (elsart

Dual excitation-emission propagation (deep) impact- FTMW spectrometer

The in-phase/quadrature phase modulation passage-acquired coherence technique(IMPACT) Fourier-transform microwave (FT-MW) spectrometer utilizing two off-axis parabolic reflectors delivers broadband capabilities at a spectral resolution similar to the resolving power of the narrowband but more sensitive coaxial beam-resonator arrangement (COBRA) FT-MW spectroscopy. Nevertheless, due to the signal pathway in the dual-path reflector arrangement, the high-frequency setup imposes a maximum applicable excitation power, thus limiting the polarization efficiency. Hence, less polar molecules were difficult to study. In a novel approach this disadvantage could be circumvented by rotating of the field vector direction of the linearly polarized microwave radiation. The setup prevails the high spectral resolution but increases the sensitivity dramatically while allowing the utilisation of very high power tube amplifiers. In this contribution we present the novel apparatus in detail as well as experimental results obtained with the modified spectrometer

Experimentelle Nachbildung von internen Kurzschlüssen in Lithium-Ionen-Pouchzellen mittels präziser Nadelpenetration

Die Lithium-Ionen-Zelle ist ein weit verbreiteter elektrischer Energiespeicher und Bestandteil vielfältiger technischer Produkte. Die bekannte Sicherheitsproblematik dieser Speichertechnologie stellt häufig größere Herausforderungen für den praktischen Einsatz dar. Das Verlassen der Betriebsgrenzen, die Einwirkung mechanischer Kräfte oder interne Produktionsfehler können aufgrund der hohen Energiedichte und der Verwendung reaktionsfreudiger Materialien zu einem „Thermischen Durchgehen“ der Zelle führen. Der interne Kurzschluss, also der zellinterne elektrisch leitende Kontakt beider Elektroden stellt hierbei einen besonders relevanten und gefährlichen Fehlerfall dar. Genau dieser Fehlerfall ist derzeit jedoch noch nicht vollständig verstanden. Ein wesentlicher Grund hierfür ist die fehlende Möglichkeit einen realitätsnahen internen Kurzschluss zuverlässig nachbilden zu können. Die derzeit häufig angewandte Nagelpenetration, als Bestandteil vieler Normen, bildet viele Fehlerursachen des internen Kurzschlusses, insbesondere die Dendritenbildung und die Partikelkontamination, aufgrund geringer Lokalität nicht realistisch nach. Sie liefert somit nur unzureichende Erkenntnisse zur Charakteristik eines solchen internen Kurzschlusses. In dieser Arbeit wird eine neue Methode zur realitätsnahen Nachbildung von internen Kurzschlüssen in Pouchzellen entwickelt und an mehr als 30 Zellen erfolgreich angewendet. Hierfür wird als Nadelpenetration eine dünne Nadel (Kanüle) präzise und mit einer geringen Vorschubgeschwindigkeit (1 µm/s) von außen in die Zelle eingestochen. Die Minimierung von äußeren Störgrößen (z.B. eine konstante Zelltemperatur) ermöglicht es, die auftretenden Streuungen auf den internen Kurzschluss selbst zurückzuführen und so eine fundierte Fehlerbewertung abzuleiten. Aus der umfangreichen Zustandscharakterisierung leitet sich bisher fehlendes Wissen zur Entstehung, Entwicklung und möglichen Detektion des internen Kurzschlusses ab, welche für die praktische Anwendung hohe Relevanz besitzen und dabei helfen, das ausgehende Risiko eines internen Kurzschlusses zu minimieren. Die Ergebnisse zeigen, dass es in vielen Fällen zu einem dynamischen Prozess der Fehlerentwicklung kommt, welcher sich insbesondere durch wiederholte kurzzeitige Spannungsabsenkung mit darauffolgender schneller Spannungserholung (Relaxation) charakterisiert. Dieser dynamische Zustand kann zum spontanen „Thermischen Durchgehen“ der Zelle führen. Oftmals bildet sich jedoch nach einigen Minuten ein konstanter hochohmiger interner Kurzschluss aus, welcher die Zelle zunächst unauffällig aussehen lässt. Besonders kritisch ist hierbei, dass für den weiteren Betrieb eine Gefährdung durch eine irreversible Strukturbeschädigung gegeben ist, die sich allerdings durch keine zerstörungsfreie elektrochemische Messmethode zuverlässig nachweisen lässt. Hieraus leitet sich als neue Erkenntnis die Notwendigkeit ab, den internen Kurzschluss sofort bei der ersten Entstehung durch eine genaue, hinreichend schnelle Spannungserfassung frühzeitig zu erkennen und daraufhin Maßnahmen zur Gefährdungsminimierung einzuleiten.The lithium-ion cell is a widely used electrical energy storage and a key component of many technical products. However, the well-known safety issues associated with this storage technology often pose major challenges for practical use. Running the cell out of operating limits, the effect of mechanical forces or internal production defects can lead to a "thermal runaway" of the cell due to the high energy density in combination with the use of reactive materials. The internal short circuit, which means the electrically conductive contact between the two electrodes inside the cell, is a particularly relevant and dangerous failure mode. Exactly this type of failure is currently not yet fully understood. One of the main reasons for this is the missing possibility to reliably reproduce a close to reality internal short circuit. Nail penetration, which is currently often used in many standards, does not realistically replicate many of the causes of internal short-circuits, particularly dendrite formation and particle contamination, due to its limited locality. Therefore, this method only provides insufficient information on the characteristics of such an internal short circuit. In this work, a new method for the realistic replication of internal short circuits in pouch cells is developed and successfully applied to more than 30 cells. For this method, a thin needle (cannula) is precisely penetrated into the cell from the outside with a low speed (1 µm/s). The minimisation of external disturbance (e.g. a constant cell temperature) makes it possible to attribute the occurring scattering to the internal short circuit itself and thus derive a well-founded failure evaluation. Comprehensive state characterisation has provided the missing knowledge on the triggering, development and possible detection of the internal short circuit, which is highly relevant for practical applications in order to minimise the outgoing risk of an internal short circuit. The results show that in many cases a dynamic process of fault development occurs, which is characterised in particular by repeated short-term voltage drops followed by rapid voltage recovery (relaxation). This dynamic state can lead to spontaneous "thermal runaway" of the cell. However, a constant high-resistance internal short circuit often develops after a few minutes, which initially makes the cell look inconspicuous. In this case, it is particularly critical that further operation is risky due to irreversible structural damage, which cannot be reliably detected by any non-destructive electrochemical measurement method. The new insight derived from this is the need to detect the internal short circuit immediately when it first occurs by precise, sufficiently fast voltage detection and then initiate actions to minimise the danger

MOLECULAR ROTATION SIGNALS: MOLECULE CHEMISTRY AND PARTICLE PHYSICS

Molecules - large or small - are attractive academic resources, with numerous questions on their chemical behaviour as well as problems in fundamental physics now (or still) waiting to be answered: Targeted by high-resolution spectroscopy, a rotating molecular top can turn into a laboratory for molecule chemistry or a laboratory for particle physics. Once successfully entrained (many species - depending on size and chemical composition - have insufficient vapour pressures or are of transient nature, such that specifically designed pulsed-jet sources are required for their transfer into the gas phase or in-situ generation) into the collision-free environment of a supersonic-jet expansion, each molecular top comes with its own set of challenges, theoretically and experimentally: Multiple internal interactions are causing complicated energy level schemes and the resulting spectra will be rather difficult to predict theoretically. Experimentally, these spectra are difficult to assess and assign. With today�s broad-banded chirp microwave techniques, finding and identifying such spectral features have lost their major drawback of being very time consuming for many molecules. For other molecules, the unrivalled resolution and sensitivity of the narrow-banded impulse microwave techniques provide a window to tackle - at the highest precision available to date � fundamental questions in physics, even particle physics � potentially beyond the standard model. Molecular charge distribution, properties of the chemical bond, details on internal dynamics and intermolecular interaction, the (stereo-chemical) molecular structure (including the possibility of their spatial separation) as well as potential evidence for tiny yet significant interactions encode their signature in pure molecular rotation subjected to time-domain microwave spectroscopic techniques. Ongoing exciting technical developments promise rapid progress. We present recent examples from Hannover, new directions, and an outlook at the future of molecular rotation spectroscopy

A HIGHLY-INTEGRATED SUPERSONIC-JET FOURIER TRANSFORM MICROWAVE SPECTROMETER

A highly integrated supersonic-jet Fourier-transform microwave spectrometer of coaxially oriented beam-resonator arrangement (COBRA) type, covering 2-20GHz, has been recently built at Chongqing University, China. _x000d_ Built up almost entirely in an NI PXIe chassis, we take the advantage of the NI PXIe-5451 Dual-channel arbitrary waveform generator and the PXIe-5654 RF signal generator to create a spectrometer with wobbling capacity for fast resonator tuning. Based on the I/Q modulation, associate with PXI control and sequence boards built at the Leibniz Universitat Hannover, the design of the spectrometer is much simpler and very compact._x000d_ The Fabry–Pérot resonator is semi-confocal with a spherical reflector of 630 mm diameter and a radius of 900 mm curvature and one circulator plate reflector of 630 mm diameter. The vacuum is effectuated by a three-stage mechanical (two-stage rotary vane and roots booster) pump at the fore line of a DN630 ISO-F 20000 L/s oil-diffusion pump. The supersonic-jet expansion is pulsed by a general valve Series 9 solenoid valve which is controlled by a general valve IOTA one driver governed by the experiment-sequence generation._x000d_ First molecular examples to illustrate the performance of the new setup will include OCS and chem{CF_3CHFCl}._x000d

The LAM of the Rings: Large Amplitude Motions in Aromatic Molecules Studied by Microwave Spectroscopy

Large amplitude motions (LAMs) form a fundamental phenomenon that demands the development of specific theoretical and Hamiltonian models. In recent years, along with the strong progress in instrumental techniques on high-resolution microwave spectroscopy and computational capacity in quantum chemistry, studies on LAMs have become very diverse. Larger and more complex molecular systems have been taken under investigation, ranging from series of heteroaromatic molecules from five-and six-membered rings to polycyclic-aromatic-hydrocarbon derivatives. Such systems are ideally suited to create families of molecules in which the positions and the number of LAMs can be varied, while the heteroatoms often provide a sufficient dipole moment to the systems to warrant the observation of their rotational spectra. This review will summarize three types of LAMs: internal rotation, inversion tunneling, and ring puckering, which are frequently observed in aromatic five-membered rings such as furan, thiophene, pyrrole, thiazole, and oxazole derivatives, in aromatic six-membered rings such as benzene, pyridine, and pyrimidine derivatives, and larger combined rings such as naphthalene, indole, and indan derivatives. For each molecular class, we will present the representatives and summarize the recent insights on the molecular structure and internal dynamics and how they help to advance the field of quantum mechanics

Precise dipole moments and quadrupole coupling constants of the cis and trans conformers of 3-aminophenol: Determination of the absolute conformation

The rotational constants and the nitrogen nuclear quadrupole coupling constants of cis-3-aminophenol and trans-3-aminophenol are determined using Fourier-transform microwave spectroscopy. We examine several $J=2\leftarrow{}1$ and $1\leftarrow{}0$ hyperfine-resolved rotational transitions for both conformers. The transitions are fit to a rigid rotor Hamiltonian including nuclear quadrupole coupling to account for the nitrogen nucleus. For cis-3-aminophenol we obtain rotational constants of A=3734.930 MHz, B=1823.2095 MHz, and C=1226.493 MHz, for trans-3-aminophenol of A=3730.1676 MHz, B=1828.25774 MHz, and C=1228.1948 MHz. The dipole moments are precisely determined using Stark effect measurements for several hyperfine transitions to $\mu_a=1.7735$ D, $\mu_b=1.5195$ D for cis-3-aminophenol and $\mu_a=0.5563$ D, $\mu_b=0.5376$ D for trans-3-aminophenol. Whereas the rotational constants and quadrupole coupling constants do not allow to determinate the absolute configuration of the two conformers, this assignment is straight-forward based on the dipole moments. High-level \emph{ab initio} calculations (B3LYP/6-31G^* to MP2/aug-cc-pVTZ) are performed providing error estimates of rotational constants and dipole moments obtained for large molecules by these theoretical methods.Comment: 9 pages, 4 tables, 3 figures (RevTeX

Systematic approach for the test data generation and validation of ISC/ ESC detection methods

Various methods published in recent years for reliable detection of battery faults (mainly internal short circuit (ISC)) raise the question of comparability and cross-method evaluation, which cannot yet be answered due to significant differences in training data and boundary conditions. This paper provides a Monte Carlo-like simulation approach to generate a reproducible, comprehensible and large dataset based on an extensive literature background on common assumptions and simulation parameters. In some cases, these assumptions are quite different from field data, as shown by comparison with experimentally determined values. Two relatively simple ISC detection methods are tested on the generated dataset and their performance is evaluated to illustrate the proposed approach. The evaluation of the detection performance by quantitative measures such as the Youden-index shows a high divergence with respect to internal and external parameters such as threshold level and cell-to-cell variations (CtCV), respectively. These results underline the importance of quantitative evaluations based on identical test data. The proposed approach is able to support this task by providing cost-effective test data generation with incorporation of known factors affecting detection quality