ISSN 0030-400X, Optics and Spectroscopy, 2006, Vol. 100, No. 6, pp. 877–880. © Pleiades Publishing, Inc., 2006. Original Russian Text © L.M. Sabirov, D.I. Semenov, 2006, published in Optika i Spektroskopiya, 2006, Vol. 100, No. 6, pp. 952–955. 877 INTRODUCTION Molecular light scattering spectroscopy is one of the most informative methods for studying liquids [1]. At low intensities of exciting radiation, a sample is mini- mally affected. For this reason, investigation of the spectral characteristics of scattered light makes it pos- sible to obtain valuable information about the behavior of static and dynamic parameters of liquid crystals (LCs) near the phase transition from an isotropic liquid (IL) to an LC. Near this transition, the susceptibility of the medium is extremely high [2]. Since the IL–LC phase transition is only slightly first-order, many properties of the isotropic phase exhibit critical behavior when the temperature approaches the phase transition temperature T c [3]. Pre- transition phenomena in the LC isotropic phase are due to the presence of correlations in the orientations of the long axes of molecules, which arise on small space– time scales through fluctuations [2]. Within the Lan- dau–de Gennes theory [4], the temperature behavior of the correlation radius ξ of fluctuations of the order parameter can be described as (1) where ξ 0 is a value of about the molecule length and T * is the temperature of the second-order phase transition (T * < T c ). At the temperature T *, the size of the ordered region (the correlation radius) becomes infinitely large. For most LCs, T c – T * ≈ 1 K. When the temperature approaches T c , the correlation radius of fluctuations increases; however, due to the first-order character of the transition, it barely reaches 10–12 nm (about 20ξ 0 ) [3]. Since fluctuations of the order parameter on the IL– LC transition are fluctuations in the spatial distribution ξ T ( ) ξ 0 T */ T T * – ( ) [ ] 1/2 , = of the axes of anisotropic molecules, the velocity of spread of these fluctuations is related to the half-width of the depolarized component of scattered light (the Rayleigh line wing) [1]: (2) where ∆ν 1/2 is the half-width of the Rayleigh line wing in inverse centimeters, c is the speed of light, and τ is the relaxation time of fluctuations of the order para- meter. For conventional liquids, the temperature behavior of the width of the Rayleigh line wing (which is caused by orientational jumps of molecules by large angles) is described well by the Debye–Stokes–Einstein hydro- dynamic equation [1] (3) Here, k is the Boltzmann constant, η is the viscosity, and V eff is the effective volume of a molecule. Within the Landau–de Gennes theory, to describe the tempera- ture behavior of the Rayleigh line wing in the LC iso- tropic phase, Eq. (3) is modified to the form [5] (4) where γ is the critical index of susceptibility of the iso- tropic phase and is a quantity having some other meaning than in (3) [6]. Experimental investigations of the birefringence in electric [7] and magnetic [8] fields, the optical Kerr effect [9], the nuclear spin–lattice relaxation [10], and the temperature behavior of the scattered light intensity [8] show that γ ≈ 1 in the LC isotropic phase. This fact ∆ν 1/2 1 π c τ --------, = ∆ν 1/2 kT π c η V eff ------------------. = ∆ν 1/2 kT T * – ( ) γ π c η V eff * --------------------------, = V eff * CONDENSED-MATTER SPECTROSCOPY Depolarized Light Scattering Spectra of the Isotropic Phase of Nematic Liquid Crystals L. M. Sabirov and D. I. Semenov Navoi State University, Samarkand, 703029 Uzbekistan e-mail: sabirov@uni.uzsci.net Received June 6, 2005 Abstract—The depolarized light scattering spectra of the isotropic phase of N-(p-methoxybenzylidene)-p- butylaniline and p-azoxy-anisole nematic liquid crystals were experimentally investigated. The limits of appli- cability of the mean field approximation of the Landau–de Gennes theory to the description of the temperature behavior of the depolarized scattering linewidth are determined. PACS numbers: 78.20.C DOI: 10.1134/S0030400X06060117