Hans Bettermann

Aggregation and Interface Behaviour of Carotenoids

Molecular aggregates attract considerable attention, as they bridge the gap between the physics of single molecules and structurally ordered crystals. Molecular self-assembly in biological systems is highly specific and fundamentally important for correct functioning in living organisms.

Identification of Xylene Isomers in High-Pressure Liquid Chromatography Eluates by Raman Spectroscopy

This contribution presents a combination of high-pressure liquid chromatography (HPLC) with a Raman spectrometer. With this approach, we have identified both isomer m-xylene and isomer p-xylene in solution at concentrations down to 10−5 mol/L. The setup was developed to analyze compounds that cannot be separated by using standard HPLC techniques.

Kinetic studies of the laser-induced photodecarbonylation of 3,5-di-tert-butyl-1,2-benzoquinone

Abstract The photodecarbonylation of 3,5-di-tert-butyl-1,2-benzoquinone was initiated by excitation of the 1 (π−π*) and the 1 ( n −π*) state, respectively, with the use of emission lines of an argon ion laser. The UV—vis reaction spectra exhibit a strong sensitivity to the selected solvents. Both UV—vis spectra and MR spectra show the existence of a persistent bis-ketene intermediate. The kinetic analysis yields that the course of reaction can be described as a consecutive process. The primary step acts as a light-induced electrocyclic ring cleavage generating the intermediate. In the second step, the CO abstraction leads to the corresponding monoketone.

Laser-induced intermolecular photocycloaddition of 3,4,5,6-tetrachloro-1,2-benzoquinone

Abstract An intermolecular [4+2] photocycloaddition was initiated by excitation of the lowest energetic 1 (π—π*) state of o -chloranil (3,4,5,6-tetr

Force field calculations for ethanedial, butanedione and some cyclic 1,2-diketones with respect to the influence of the intercarbonyl dihedral angle on their vibrational frequencies

Abstract The molecular vibrations of ethanedial, butanedione and some cyclic 1,2-diketones are calculated by means of normal coordinate analyses. Starting from published ab initio force constants, Simplex-optimized force fields are developed. Using these force fields, all vibrational frequencies of ethanedial and the carbonyl stretching vibrations of the cyclic 1,2-diketones are calculated for different intercarbonyl dihedral angles.

Local In-Situ Analysis of PEM Fuel Cells by Impedance Spectoscopy and Raman Measurements

An understanding of the processes inside of low temperature fuel cells on a local scale is required for an effective improvement strategy. For this purpose in situ Raman spectroscopy and local impedance spectroscopy is being developed. The contribution describes the modifications to the cell, and installations of additional devices and the experimental detection systems for integrating both methods into a single cell set up. First results to verify the combined results were carried out and are presented. In the case of the local impedance with segmented cells the additional effort for the simultaneous frequency analysis of all segments is described. The Raman signals of hydrogen, oxygen and water from the channels of the flow field are shown and first measurements of gas composition along the fuel path are analyzed.

Identification of Triplet States in Carotenoids by Intracavity Absorption Spectroscopy and Measurements of Delayed Fluorescence

Owing to the low quantum yield of phosphorescence, triplet states of carotenoids have been very difficult to identify. These states can be characterized by intracavity absorption spectroscopy, which allows the direct measurement of the spin-forbidden singlet-triplet transitions in low concentrated solutions, and by delayed fluorescence measurements.

Dual fluorescence of diapocarotenoids

Abstract This article presents syntheses, absorption spectra and fluorescence measurements of three diapocarotenoids with different chain lengths (7,9 and 11 conjugated double bonds). These compounds exhibit S2-S0 as well as S1-S0 fluorescence. The feature of total luminescence depends strongly on the choice of the solvents and the concentrations of the solutes.

Scanning tunneling microscopy of laser excited graphite

Under normal scanning conditions, only each second carbon atom of the top layer of highly-oriented pyrolytic graphite (HOPG) is usually visible in scanning tunneling microscopy (STM). When irradiating HOPG with a HeNe laser light (623 nm), each carbon atom of the top layer is visible and the STM image changes from trigonal to hexagonal symmetry. This effect is reversible by simply interrupting the laser light flux.

The quantitative determination of the S0—T1 absorption in pyrene with the use of intracavity absorption spectroscopy

Abstract The spin-forbidden S 0 — T 1 transition of pyrene was quantitatively investigated by applying intracavity absorption spectroscopy. The measurements were carried out in benzolic solutions. The molar decadic extinction coefficient of the 0—0 transition was determined to 6.0 × 10 −4 dm 3 mol −1 cm −1 . The integral absorptivity was calculated to 2.94 × 10 −2 dm 3 mol −1 cm −1 and yielded an intrinsic phosphorescence lifetime of 55.4 s. The intracavity absorptions were measured in a cavity-dumped Rhodamine 6G dye laser. Absorbances were recorded in the range between 8 × 10 −4 and 5 × 10 −6 .