Overtone spectroscopy of some benzaldehyde derivatives

Overtone spectrum of o, m and p-nitrobenzaldehydes and p-chlorobenzaldehyde has been studied in 2000–12000 cm⁻¹ region. Vibrational frequencies and anharmonicity constants for aryl as well as alkyl CH stretch vibrations have been determined. We have also determined the internuclear distances for the aryl CH bond in the different molecules. The small variation observed in these distances is an indication of the substitution effect. It is observed that in the case of p-disubstituted benzens, the shift in aryl CH bond is proportional to sum of the Hammet σ of the substituents. However in the case of o-disubstituted benzenes it is only 80% of the para-substituted shift.     

Resistance minima in amorphous PdSi alloy

The resistivity minimum in amorphous PdSi containing transition metals is magnetic in origin. For high purity samples a weak minimum, possibly associated with residual Fe impurity, is removed by a mild heat-treatment known to reduce the density of localized “tunneling” states.     

NSLS‐II: A proposed new synchrotron at Brookhaven National Laboratory

A workshop on high-resolution X-ray emission spectroscopy was held in conjunction with the joint NSLS/CFN 2006 Users' Meeting. With the availability of high-brightness X-ray sources, and the development of improved optics and detectors for high-resolution (millivolt to volt) X-ray detection, X-ray emission spectroscopy (XES) has become one of the more rapidly growing areas of condensed matter synchrotron science. Most of the applications to date have focused on using XES for problems in condensed matter physics. The goal of this workshop was to illustrate the potential of XES for addressing important questions in chemistry and biology.     

Development of new apertures for coherent X‐ray experiments

When one performs a coherent small‐angle X‐ray scattering experiment, the incident beam must be spatially filtered by slits on a length scale smaller than the transverse coherence length of the source which is typically around 10 µm. The Fraunhofer diffraction pattern of the slit is one of the important sources of background in these experiments. New slits which minimize this parasitic background have been designed and tested. The slit configuration apodizes the beam by the use of partially transmitting inclined slit jaws. A model is presented which predicts that the high wavevector tails of the diffraction pattern fall as the inverse fourth power of the wavevector instead of the inverse second power that is observed for standard slits. Using cleaved GaAs single‐crystal edges, Fraunhofer diffraction patterns from 3 and 5.5 keV X‐rays were measured, in agreement with the theoretical model proposed. A novel phase‐peak diffraction pattern associated with phase variations of the transmitted electric field was also observed. The model proposed adequately accounts for this phenomenon.