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R Flesch

Publications and source records attributed to R Flesch.

At least 19 recordsLinked to original sources
PubMed2006

Radiative relaxation and fragmentation dynamics of S 2p-excited hydrogen sulfide.

Radiative relaxation of S 2p-excited hydrogen sulfide (H(2)S) is investigated by dispersed ultraviolet and visible fluorescence spectroscopies. We observe distinct changes in the fluorescence spectra as a function of excitation energy. Excitation to Rydberg states below the S 2p ionization threshold yields intense fluorescence from neutral and ionic atomic fragments (H, S(+), and S(2+)). In addition to the atomic emission, fluorescence of the molecular fragment ion HS(+) is preferably found after excitation of the S 2p electron into the unoccupied 6a(1) and 3b(2) orbitals with sigma(*) character. This is interpreted as evidence for ultrafast dissociation of the core-excited molecule prior to electronic relaxation. The rotationally resolved fluorescence spectra of the A (3)Pi-->X (3)Sigma(-) transition are analyzed in terms of the fragmentation dynamics leading to the formation of the excited molecular fragment ion, where changes in bond angle are discussed in terms of the rotational population.

Journal Article↗
PubMed2006

Shape resonances in molecular clusters: the 2t(2g) shape resonances in S 2p-excited sulfur hexafluoride clusters.

Sulfur hexafluoride clusters are investigated in the S 2p excitation regime. For the first time special emphasis is put on high-energy resolution spectroscopy of shape resonances in free clusters. We have investigated the 2t(2g)-shape resonance occurring above the S 2p threshold as one typical example to study size effects that are related to shape resonances. A small redshift of this resonance of 30 +/- 5 meV occurs in clusters relative to the free molecule and changes in line shape are observed. A double-barrier optical potential model is applied for the analysis of intra- and intermolecular effects occurring in SF6 clusters, which is suitable for rationalizing the experimentally observed spectral changes. The experimental and theoretical results are briefly discussed in comparison to previous work on core-excited van der Waals clusters containing diatomic molecules.

Cluster Analysis↗
PubMed2006

C 1s -->pi* excitation in variable size benzene clusters.

The C 1s -->pi* transition in molecular benzene and benzene clusters is investigated by photoion yields at high energy resolution. The vibrationally resolved band shows the same shape in clusters as in the bare molecule, but it is redshifted by 50 meV in small clusters, i.e. near the threshold of cluster formation. This redshift increases to 70 meV with increasing cluster size. The results are assigned in comparison with ab initio calculations on model structures of dimers, trimers, and tetramers. These indicate that different carbon sites in the molecular moieties give rise to distinct spectral shifts, where carbon sites that are pointing to the pi-system of another molecule show a larger redshift than the other ones. Such structural properties are found in solid benzene, so that the gas-to-solid shift of C 1s -->pi* excited benzene is derived to be a redshift which is of the order of 100-180 meV.

Benzene↗
PubMed2006

Charging mechanisms of trapped element-selectively excited nanoparticles exposed to soft x rays.

Charging mechanisms of trapped, element-selectively excited free SiO2 nanoparticles by soft x rays are reported. The absolute charge state of the particles is measured and the electron emission probability is derived. Changes in electron emission processes as a function of photon energy and particle charge are obtained from the charging current. This allows us to distinguish contributions from primary photoelectrons, Auger electrons, and secondary electrons. Processes leading to no change in charge state after absorption of x-ray photons are identified. O 1s-excited SiO2 particles of low charge state indicate that the charging current follows the inner-shell absorption. In contrast, highly charged SiO2 nanoparticles are efficiently charged by resonant Auger processes, whereas direct photoemission and normal Auger processes do not contribute to changes in particle charge. These results are discussed in terms of an electrostatic model.

Journal Article↗
PubMed2005

Bond strength of chlorine peroxide.

The bond strength of chlorine peroxide (ClOOCl) is studied by photoionization mass spectrometry. The experimental results are obtained from the fragmentation threshold yielding ClO+, which is observed at 11.52 +/- 0.025 eV. The O-O bond strength D(o) is derived from this value in comparison to the first ionization energy of ClO, yielding D(o)298 = 72.39 +/- 2.8 kJ mol(-1). The present work provides a new and independent method to examine the equilibrium constant K(eq) for chlorine peroxide formation via dimerization of ClO in the stratosphere. This yields an approximation for the equilibrium constant in the stratospheric temperature regime between 190 and 230 K of the form K(eq) = 1.92 x 10(-27) cm3 molecules(-1) x exp(8430 K/T). This value of K(eq) is lower than current reference data and agrees well with high altitude aircraft measurements within their scattering range. Considering the error limits of the present experimental results and the resulting equilibrium constant, there is agreement with previous works, but the upper limit of current reference values appears to be too high. This result is discussed along with possible atmospheric implications.

Journal Article↗
PubMed2004

Cluster size effects in core excitons of 1s-excited nitrogen.

Cluster size effects in core excitons below the N 1s ionization energy of nitrogen clusters are reported in the energy regime 405-410 eV. These results are compared to the molecular Rydberg states as well as the corresponding bulk excitons of condensed nitrogen. The experimental results are assigned using ab initio calculations. It is found that the lowest excitons (N 1s-->3ssigma and N 1s-->3ppi) are blueshifted relative to the molecular Rydberg transitions, whereas others (N 1s-->3dpi and N 1s-->4ppi) show a redshift. Results from ab initio calculations on (N(2))(13) clearly indicate that the molecular orientation within a cluster is critical to the spectral shift, where bulk sites as well as inner- and outer-surface sites are characterized by different inner-shell absorption energies. These results are compared to the experimental spectra as well as previous work on site-selectively excited atomic van der Waals clusters, providing an improved spectral assignment of core exciton states in weakly bound molecular clusters and the corresponding condensed phase.

Journal Article↗
PubMed2004

Mechanism of anion formation in C 1s-->pi*-excited carbon dioxide.

The mechanism of anion formation from core-excited carbon dioxide is investigated in the C 1s-excitation regime (280-340 eV), where negative-ion-positive-ion coincidences and negative-ion-positive-ion-positive-ion coincidences experiments are performed. O(-) formation occurs efficiently upon C 1s-->pi(*)-excitation (290.7 eV) from the singly charged cation CO(2) (+). This anion is measured in coincidence with the singly charged atoms C(+) and O(+). The formation of atomic cations is accompanied by a substantial kinetic energy release. This suggests that an intermediate CO(++) is formed together with O(-), where the dication decays via fission. The results are discussed in terms of an anion formation mechanism from core-excited molecules considering previous experimental results.

Journal Article↗
PubMed2002

Charge localization in collision-induced multiple ionization of van der Waals clusters with highly charged ions.

Charge localization in multiple ionization and fragmentation of small argon clusters is reported. The processes are initiated by interaction of the neutral cluster with highly charged Xe(q+) (5< or =q< or =25). Products are detected by means of multicoincidence time-of-flight methods. A strong dependence of the fragmentation pattern on the Xe charge state q is observed. In particular, we find evidence for formation of multiply charged atomic Ar(r+) fragment ions up to r = 7. Such high charge states have neither been observed in fission of multiply charged van der Waals clusters nor in ion-induced fragmentation of fullerenes or metal clusters. This hints at fundamentally different excitation and fragmentation dynamics.

Journal Article↗
PubMed2001

Dynamic stabilization in 1sigma(u)-->1pi(g) excited nitrogen clusters.

High-resolution 1s near-edge spectra of molecular nitrogen and variable size nitrogen clusters obtained using monochromatic synchrotron radiation from the high brilliance BESSY-II storage ring facility are reported. The vibrationally resolved 1sigma(u)-->1pi(g) core-to-valence excitation band of clusters shows a distinct redshift of 6+/-1 meV relative to the isolated molecule, but the vibrational structure and linewidths are essentially unchanged. This shift is assigned to dynamic stabilization of 1sigma(u)-->1pi(g) excited molecules in clusters, arising from the dynamic dipole moment generated by core-hole localization in the low-symmetry cluster field. This leads to changes in intermolecular interactions compared to the ground-state cluster. Such spectral shifts are expected to occur generally in molecular clusters and in the corresponding condensed phase.

Journal Article↗
PubMed2001

Progress on inner-shell excitations of molecular van der Waals clusters.

Recent progress on core-level excitation of molecular van der Waals clusters is reported. Resonant excitation near element K edges of isolated and clustered molecules gives rise to small spectral shifts that can only be detected with high spectral resolution. This requires the use of state-of-the-art storage-ring facilities along with insertion devices and high-resolution soft X-ray monochromators. Selected experimental results on carbon monoxide clusters are reported. For the vibrationally resolved C 1s --> pi* (v = 0) band of clustered CO, these indicate characteristic line broadening as well as a small red shift of 2 +/- 1 meV compared with the isolated molecule. The results are discussed within the framework of the quasi-atomic approach with respect to intermolecular interactions, freezing of molecular rotations in clusters, and dynamic localization of resonant core-to-valence excitations.

Journal Article↗
PubMed1989

Antibacterial chemotherapy for treatment of infections in outpatient surgery.

126 patients with surgical infections of different severity were treated intravenously with ceftriaxone (Rocephin) 2 or 1 g once a day in less serious cases. We did not observe any severe drug reaction; the duration of therapy varied between 1 and 7 days. Ceftriaxone is a very powerful broad-spectrum antibacterial drug. Treatment with a single injection or infusion per day saves costs and avoids hospitalisation: ceftriaxone is thus the ideal antibacterial drug for the ambulatory patient.

Ambulatory Surgical Procedures↗
PubMed1984

[Radiation-induced chondrosarcoma of the scapula following mastectomy].

In the medical literature we found published four cases of irradiation induced chondrosarcoma of the scapula. We present a fifth one and report about a 63 year old female patient. She underwent a left radical mastectomy for breast cancer. Pre- and postoperatively a local irradiation of 140,00 Gy was applied. After a disease free interval of 18 years a large tumor in the left scapula was histologically confirmed as a chondrosarcoma. All criterias of Cahan for an irradiation induced sarcoma are fulfilled.

Bone Neoplasms↗
PubMed1981

[The physician's liability from the viewpoint of a university surgery department].

Malpractice suits against physicians have increased tremendously during the last years. We have analysed 108 cases with alleged malpractice. Twenty-two suits had not been settled yet at the time of this study. The documents were not available in twenty-one cases. There were court decisions in 65 cases. Fourty-eight times the accused physicians could be exculpated. In 12 cases a settlement out of court could be reached. The accused physician was found guilty in 4 cases. Reduction in the number of malpractice suits can be achieved in our opinion by exact documentation of clinical findings and laboratory results as well as by a better and more detailed information of the patients.

Abdomen↗
PubMed1976

[Nodular fascitis].

Since 1971 four cases of Fasciitis nodularis were treated by the outpatient-department of the Surgical Clinic, Univ. of Erlangen. Alieno loco one patient's disease had been diagnosed as sarcoma, another patient had a lesion operated on which had been suggested being malignant by a pathologist. The danger in Fasciitis nodularis is, that it is easily considered a malignant process and therefore too radical a tumor therapy is performed. The differential diagnosis from clinical and histological point of view between Fasciitis nodularis and soft tissue tumors is presented.

Adult↗