Index of content:
Volume 117, Issue 23, 15 December 2002
Dramatic relativistic effects in atomization energy and volatility of the superheavy Hassium tetroxide and117(2002); http://dx.doi.org/10.1063/1.1527057View Description Hide Description
Ab initio all-electron relativistic Dirac–Fock (DF) and nonrelativistic (NR) Hartree–Fock (HF) self-consistent field (SCF) molecular calculations are reported for the tetrahedral superheavy hassium tetroxide and its lighter congener at various M–O bond lengths. Our relativistic DF and NR HF wave functions predict the ground state of the tetrahedral and to be bound and the predicted relativistic (nonrelativistic) atomization energy for and is 15.35 (6.83) and 10.32 (5.59) eV, respectively. Relativistic effects lead to dramatic increase of ∼225% and 185% in the predicted of and respectively. Mulliken population analysis of our relativistic DF (NR HF) wave functions for the and yields a charge on Hs of +1.06 (+1.14) and Os of +0.88 (+1.94), respectively. Our DF SCF wave function, in contrast to our NR HF wave function, predicts to be more ionic, i.e., less volatile than and our prediction is in agreement with the recent experimental work for the superheavy element hassium (http://enews.lbl.gov/Science-Articles/Archive/108-chemistry.html, dated 4 June 2001).
117(2002); http://dx.doi.org/10.1063/1.1527893View Description Hide Description
Pulsed, visible and near-infrared laser light is coupled into an optical fiber, which is wound into a loop using a fiber splice connector. The light pulses traveling through the fiber-loop are detected using a photomultiplier detector. It is found that once the light is coupled into the fiber it experiences very little loss and the light pulses do a large number of round trips before their intensity is below the detection threshold. Measurements of the loss-per-pass and of the ring-down time allow for characterization of the different loss mechanisms of the light pulses in the fiber and splice connector. This method resembles “cavity ring-down absorptionspectroscopy” and is well suited to characterize low-loss processes in fiber optic transmission independent from power fluctuations of the light source. It is demonstrated that by measuring the ring-down times one can accurately determine the absolute transmission of an optical fiber and of the fiber connector. In addition it is demonstrated that the technique is useful as an absorptionspectroscopic technique of very small sample volumes. A solution of an organic dye was placed between the fiber ends instead of the usual index matching fluid, and an absorptionspectrum of of the dye -diethyl--dicarbocyanine iodide in of dimethylsulfoxide was recorded.
117(2002); http://dx.doi.org/10.1063/1.1527943View Description Hide Description
Entanglement effects in polymer melts are investigated using mode coupling theory. For a system of long thin rods that perform only translation motion, we find an exact solution to the mode coupling theory, and demonstrate that it predicts that the self-diffusion coefficient becomes isotropic as the aspect ratio becomes infinite, i.e., it does not describe entanglement effects. One has to go beyond the usual Gaussian approximation in mode coupling theory to obtain nontrivial results for the self-diffusion coefficient, and a simple approximation is investigated which gives results consistent with the reptation theory and a dynamical mean field theory.