Spin-lattice relaxation of linear triplet excitons in tetrachlorobenzene at high magnetic fields

Spin-lattice relaxation of linear triplet excitons in 1,2,4,5-tetrachlorobenzene has been studied by an optical method at high magnetic fields B and at low crystal temperature. We find the interesting result that the field dependence of the relaxation rate constants for the direct processes cannot be described by a simple B³ law. The experimental relaxation rate for the Δm = 2 transition increases as B², and for the Δm = 1 transition as B^2,6.     

Über die ozonisierungsreaktion von jod in wasserfreiem fluorwasserstoff und die hydrolyse von jodtrifluorid

From the reaction of elemental iodine with ozone in anhydrous HF crystalline iodine trifluoride is formed. The hydrolysis of iodine trifluoride in HF yields a colourless crystalline solid. The Raman spectra of both compounds are described.     

FLUORESCENCE YIELD PROPERTIES OF A FRACTION ENRICHED IN NEWLY SYNTHESIZED BACTERIOCHLOROPHYLL U-PROTEIN COMPLEXES FROM RHODOPSEUDOMONAS SPHAEROIDES

Abstract— A membrane fraction enriched in newly synthesized bacteriochlorophyll a-protein complexes was isolated from Rhodopseudomoms sphaeroides by rate-zone sedimentation. An examination of the fluorescence yield properties showed that the ratio of the maximal fluorescence emission near 910 nm (with all photochemical traps closed) to that of the initial fluorescence rise (with all traps open) was 2.2 compared to 2.9 in chromatophores. The spectrum for the variable portion of the fluorescence emission (the slow rise between the initial and maximal levels) was essentially the same in both fractions, but that observed for the initial rise in the newly synthesized material showed a greater fluorescence yield with a broad peak near 865 nm. This extra emission is thought to arise from the light-harvesting bacteriochlorophyll complex with an absorption maximum at 850 nm and suggests that this component is only partially connected to photosynthetic units. In contrast, the little extra emission observed at the longer wavelengths in this fraction indicated that energy is transferred more efficiently between the 875 nm antenna complex and photochemical reaction centers. The kinetics of the fluorescence rise suggest that photosynthetic units exist at separate sites in newly synthesized membrane regions.     

Pulsed ion beam irradiation effects on surfaces of polymeric materials

Various polymers were irradiated with high energy ( keV) carbon and hydrogen ion beams obtained from a high intensity pulsed power source. Energy deposition was in the range of 0.1–5 J/cm² during each pulse, and ion penetration was limited to a few microns. The rapid energy deposition (<500 ns) corresponded to a dose rate of approximately 10¹² Gy/s and resulted in a considerable temperature rise in the surface material accompanied by the formation of gaseous radiolysis products in amounts as high as the volume of the surface layer in which they were formed. Analysis by scanning electron microscopy revealed that dramatic changes to the polymer surface had occurred in some (but not all) of the materials, which took the form of extensive porosity or roughening. © 1998 John Wiley & Sons, Ltd.     

Generation of far-infrared pulses by use of a passively mode-locked high-pressure CO2 laser

Summary Our present study demonstrates for the first time generation of frequency-tunable intense infrared radiation pulses in the nanosecond time regime by mode-locking a high pressure CO₂ laser using p-doped germanium as a saturable absorber. These pulses were transferred into the FIR region via stimulated Raman scattering of the CO₂ laser radiation in CH₃F resulting in subnanosecond FIR laser pulses.     

Metallocenylborane III. Darstellung und eigenschaften von ferrocenyl- und cymantrenylboranen

Ferrocene, cymantrene and methylcymantrene react with BI₃, BBr₃, C₆H₅BI₂ and CH₃BI₂ in boiling CS₂ or C₆H₁₂ forming air-sensitive metallocenylhaloboranes. The direct dichloroborylation is only possible with ferrocene. Starting from metallocenyliodoboranes the corresponding substituted metallocenylboranes are obtained by halogen exchange with AsF₃ or AsCl₃, by methylation with Sn(CH₃)₄, by ether cleavage of (C₂H₅)₂O, by redox reaction with (CH₃S)₂ and by reaction with R₂NH. ¹H and ¹³C NMR spectra indicate that in contrast to cymantrenylhaloboranes, in ferrocenylhaloboranes the 3,4-protons are more deshielded than the 2,5-protons. The metallocenylboranes, isoelectronic with α-metallocenylcarbenium ions, are weaker Lewis acids than phenylboranes; they form donor-acceptor compounds with pyridine and dimethylsulfane, respectively.     

Are there “prompt” like-sign dimuons?

From exposures of the CDHS detector at the CERN SPS we have obtained 367μ ⁺ μ ^? events in neutrino beams and 73μ ⁺ μ ⁺ events in an antineutrino beam. The magnitude of a prompt like-sign signal has been controversial in the past and moreover could not be explained by known production mechanisms. A critical discussion of the experimental situation is given. We have tried to reduce the systematic uncertainties of previous experiments and to get more information on the dependence of the signal with energy and the muon momentum cut-off. This experiment yields a signal of 2.8σ (2.4σ) of prompt like-sign dimuon events in the case of neutrinos (antineutrinos). The rate to charged current events is of the order of 10^?4 forp _μ<9GeV andE>100 GeV. The prompt signal has all the properties expected from the production and decay of charm-anticharm events. The magnitude, however, is substantially higher then the prediction of perturbative QCD but lower than some other experiments.     

Response of a Bloch oscillator to a THz-field

In this paper we report on the observation of response of a Bloch oscillator at room temperature to a THz-field of a frequency larger than the Bloch frequency. The oscillator consisted of a semiconductor superlattice structure, with an applied dc voltage giving rise to a dc electron drift current. Submitting the oscillator to a field at a frequency of 3.3 THz caused a sizeable reduction of the current; the THz-field was generated by use of intense THz-radiation pulses focused on an antenna coupled to the superlattice. We attribute the THz-field induced reduction of the current to a frequency modulation of the Bloch oscillations of electrons at the frequency of the THz-field, leading to reduction of the electron drift velocity and, consequently, of the current.