Abstract: | Using methods of statistical thermodynamics, it is shown that after pulse excitation the evolution of a “polar luminescent
probe—polar disordered medium” system is described by an equation of damping vibrations. This allows the conclusion that in
the solvate shell of the probe molecule synchronous rotational vibrations (librations) of the molecules of the medium occur,
whose damping is caused by dielectric friction. Such a collective synchronous motion is considered as a motion of a quasiparticle
called a hyston. The moment of inertia Jn and mass Mh of a hyston are defined as Jh=2m2
1a-3Ω0
-2(ε-1)/(2ε+1), Mh=JhMs/Js, where m1 is the dipole moment of the probe molecule in the excited S1-stute; a is the Onsager radius; Ω0 is the cyclic frequency of harmonic vibrations of the hyston; ε is the dielectric constant; Ms and Js are the mass and moment of inertia of a molecule of the medium, respectively. The correlation function of the motion of the
molecules c(t) is a solution of the equation of hyston motion. The fluorescence response s(t) in measurements with time resolution
coincides with the correlation function: s(t)=c(t). The concepts concerning hystons make it possible to describe macroscopic
photoinduced coherent motion that is manifested against a background of thermal motion of the medium molecules.
Institute of Molecular and Atomic Physics, National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus.
Translated from Zhurnal Prikladnei Spektroskopii, Vol 65, No. 2, pp. 176–183, March–April, 1998. |