A Combined Spectrophotometer and Fluorometer to Demonstrate the Principles of Absorption Spectroscopy

A dual-function student-crafted instrument is described as part of a laboratory activity aimed to teach both the principles and practical aspects of absorption spectroscopy to secondary and introductory undergraduate students. Using minimal changes in an arrangement that is based on interlocking bricks and low-cost components, both a fluorometer and photometer have been constructed. The former demonstrates the principles of the Beer–Lambert law visually and quantitatively by acquiring the spatial light attenuation through a fluorescent sample. The latter then demonstrates its practical application in a visible-light spectrometer by measuring the absorption spectrum of an aqueous permanganate solution

Nonthermal fragmentation of C60

A theoretical study of the subpicosecond fragmentation of C60 clusters in response to ultrafast laser pulses is presented. We simulate the laser excitation and the consequent nonequilibrium relaxation dynamics of the electronic and nuclear degrees of freedom. The first stages of the nonequilibrium dynamics are dominated by a coherent breathing mode followed by the cold ejection of single C atoms, in contrast to the dimer emission which characterizes the thermal relaxation. We also determine the nonequilibrium damage thresholds as a function of the pulse duration.Comment: 5 pages, 4 figures, submitted to Chem. Phys. Let

Metastable Dynamics of the Hard-Sphere System

The reformulation of the mode-coupling theory (MCT) of the liquid-glass transition which incorporates the element of metastability is applied to the hard-sphere system. It is shown that the glass transition in this system is not a sharp one at the special value of the density or the packing fraction, which is in contrast to the prediction by the conventional MCT. Instead we find that the slowing down of the dynamics occurs over a range of values of the packing fraction. Consequently, the exponents governing the sequence of time relaxations in the intermediate time regime are given as functions of packing fraction with one additional parameter which describes the overall scale of the metastable potential energy for defects in the hard-sphere system. Implications of the present model on the recent experiments on colloidal systems are also discussed.Comment: 21 pages, 5 figures (available upon request), RevTEX3.0, JFI Preprint