The electron spin resonance line shape for the Δm=2 transition of randomly oriented aromatic molecules in a triplet state is analyzed. This is an extension of the treatment of van der Waals and de Groot to molecules having less than ternary symmetry. In the present paper the spectrum of a molecule is approximated by a Gaussian function of constant width and the electron g tensor is assumed to be isotropic. The various stages of the calculation have been fitted into a computer program, using as input data the principal values of the electron spin-spin coupling tensor. The calculations show that a characteristic structure may be present in the spectrum. The experimental spectra of naphthalene and its deuterated homologue present in effect enough of this structure to make it possible to determine the absolute values of the two constants characterizing the electron spin—spin interaction.
The structure in the electron-spin-resonance spectrum of randomly oriented molecules in a triplet state is due to resonance fields stationary with respect to a change in the molecular orientation. This is the basis for the derivation of the electron spin—spin coupling constants from such spectra. In this paper we investigate this structure with the help of a computer program which generalizes the one described in Part I to deal with the so-called Δm=2 spectra. Some rules are derived for the interpretation of spectra. We then examine the possibility of including in such calculations the anisotropy of the electron g tensor and some dependence on the orientation of the linewidth. For the canonical orientations, the linewidth in a variable-magnetic-field experiment is shown not to depend on the microwave quantum.
The dynamics of the Time-Dependent Fluorescence Shift (TDFS) of a rigid polar excited probe dissolved in alcohol solvents at different temperatures have been studied by picosecond time-resolved spectroscopy. The results are compared to previously published results on well characterized polar systems. These results show that solvation dynamics in such systems are strongly scaled by the microscopic (singleparticle) reorientation time xM of the solvent molecules and/or by the (macroscopic) longitudinal relaxation time XL of the solvent. The key point governing this scaling is the relative interaction between the solvent molecules and the probe compared to the interaction between the solvent molecules. It is also shown that specific interactions, such as hydrogen bonded-complex formation, may play an important role. KEY WORDS" Solvation dynamics, picosecond TDFS, dielectric phenomena.
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