A review of two decades of the analysis of hyperfine parameter distributions in Mössbauer spectroscopy: Difficulties,progress and prospects

We present a review of the most used methods used to obtain hyperfine parameter distributions and discuss the mathematical problems. The Czjzek model and extensions for an EFG distribution in random systems is critically reviewed     

Amplitude modulation of submillimeter wave gyrotron output

Amplitude modulation of gyrotron by a small modulation of the anode voltage is calculated using an energy transfer formula. Experimental measurements using a submillimeter wave gyrotron are in good agreement. One hundred percent modulation of the output at frequencies up to several hundred kilohertz has been achieved with anode modulation levels of only a few percent. Numerical calculations lend further support to the experimental results.     

How and why do transition dipole moment orientations depend on conformer structure?

A remarkable influence of the orientation of a polar side chain on the direction of the S(1) ← S(0) transition dipole moment of monosubstituted benzenes was previously reported from high-resolution electronic spectroscopy. In search for a more general understanding of this non-Condon behavior, we investigated ethylamino-substituted indole and benzene (tryptamine and 2-phenylethylamine) using ab initio theory and compared the results to rotationally resolved laser-induced fluorescence measurements. The interaction of the ethylamino side chain with the benzene chromophore can evoke a rotation and a change of ordering of the molecular orbitals involved in the excitation, leading to state mixing and large changes in the orientation of the excited-state transition dipole moment. These changes are much less pronounced in tryptamine with the indole chromophore, where a rotation of the transition dipole moment is attributed to Rydberg contributions of the nitrogen atom of the chromophore. For phenylethylamine, a strong dependence of the oscillator strengths of the lowest two singlet states from the conformation of the side chain is found, which makes the use of experimental vibronic intensities for assessment of relative conformer stabilities at least questionable.     

A rotationally-resolved Rydberg transition of I2

Rotationally-resolved bands leading to a Rydberg state R 0 _u ⁺ of molecular I₂ are observed in a two-stage, three-photon transition from the ground state. The R 0 _u ⁺ state interacts homogeneously with high vibrational levels, ν_F ≈ 200–250, of an ionic state F 0 _u ⁺, the perturbation being directed by the vibrational overlap integrals towards even-numbered vibrational levels of R. Spectral constants of R 0 _u ⁺ are (in cm^-1): T _e = 61665·15, ω_e = 209.29, ω_e x _e = 0·859, B _e = 0·03842 and α_e = 1·6 × 10^-4. The electronic matrix element for the R, F interaction (excluding one deviant result) is |W _e| = 107 ± 1 cm^-1; thus W _e/ω_e ≈ 0·5, corresponding to ‘intermediate’ coupling. Energy considerations indicate that R should be assigned to the 0 _u ⁺ state of either the configuration (2430 Π_1/2g )6pσ _u , or of (2421 ⁴Σ _u ^-)6sσ _g . This state is the first extra-valence state of I₂ to be rotationally analysed.     

External noise and its interaction with spatial degrees of freedom in nonlinear dissipative systems

A brief introduction to the field is given together with an overview of the lectures given at the workshop on External Noise and its Interaction with Spatial Degrees of Freedom in Nonlinear Dissipative Systems organized by the Center for Nonlinear Studies at Los Alamos, March 28–31, 1988. It is hoped that the publication of papers presented at the workshop in a single issue of theJournal of Statistical Physics will help draw attention to the recent developments in this rapidly area of nonequilibrium phenomena.