The Raman spectrum of NH4Cl has been studied as a function of temperature and pressure close to the multicritical point at which the λ-transition changes from first to second order. Variations in the intensities of appropriate bands have been used to calculate the critical exponents for the order parameter. By varying the temperature at fixed pressures of zero, 3.0 k bar and 1.5 k bar, exponent values of β = 0.154 ± 0.012, β = 0.33 ± 0.06 and β = 0.26 ± 0.06 have been obtained for the first-order, second-order and multicritical regions respectively. Our first-order exponent value is close to that observed by previous workers, our second-order value is close to that predicted by the three dimensional Ising model, and our multicritical value is close to that predicted by mean field theory.


SHERMAN, WF; Yurtseven, Hasan Hamit (1986-03-01)
Raman spectroscopy has been used to study the λ-transition regions of NH4Cl and NH4Br. An Ising pseudospin-phonon coupled model has been fitted to the observed Raman data. In particular we report here the results of fitting the model to the frequencies and damping constants of the non-soft TO component of the lattice modes of NH4Cl and NH4Br. Both crystals have the orientations of their NH+4 ions disordered at temperatures above their λ transitions, and have (orientation-ignored) Oh structures (β) containin...
Dielectric Properties of Ethanol and Gasoline Mixtures by Terahertz Spectroscopy and an Effective Method for Determination of Ethanol Content of Gasoline
ARIK, Enis; Altan, Hakan; Esentürk, Okan (American Chemical Society (ACS), 2014-05-01)
Investigation of frequency dependent permittivity of mixture solutions provides information on the role of intermolecular interactions on relaxation processes of solvent and solute molecules. In this study the dielectric properties of ethanol/gasoline mixtures in the terahertz spectral region are investigated. Frequency dependent absorption coefficients, refractive indices, and complex permittivities of pure ethanol and gasoline, and their mixtures at varying ethanol volume percentages (v/v %) are reported....
Raman Study of Solid Nitrogen in the beta Phase and Close to the Melting Line
Iseri, E. Cetinbas; Yurtseven, Hasan Hamit (Walter de Gruyter GmbH, 2013-02-01)
This study gives the Raman frequencies calculated as functions of temperature and pressure for the lattice modes in the solid beta phase and close to the melting line (beta-fluid transition). The experimental volume data from the literature is used to calculate the Raman frequencies for the molecular nitrogen system. Some observed Raman frequencies are also used as the initial data to perform our calculations given here.
Thermodynamic Parameters of Cholesteric/Smectic A Transition in Cholesteric Myristate and Its Binary Mixture CM/PCPB
Yurtseven, Hasan Hamit (Pleiades Publishing Ltd, 2018-06-01)
Thermodynamic properties of the cholesteryl myristate (CM) and its binary mixture CM/PCPB (p-pentylphenyl-2-chloro-4(p-pentylbenzoyl)-benzoate) are studied at the concentrations of x (PCPB) = 0.052 and 0.219 as a function of temperature near the cholosteric/smectic A transition. By analyzing the observed molar volume from the literature, the temperature dependences of the thermal expansion, isothermal compressibility and the difference in the specific heat are calculated and, the Pippard relations are estab...
Raman bandwidths calculated for the librational ( a -phase) and internal (8, d loc and d phases) modes in solid N 2 using pseudospin-phonon coupling (PS) and energy-fluctuation (EF) models
Yurtseven, Hasan Hamit (Elsevier BV, 2020-10-01)
This study gives the calculation of the Raman bandwidths using the models of the pseudospin-phonon coupling (PS) and energy fluctuation (EF) where the Raman frequency calculated from the molecular field theory, is considered as the order parameter close to the phase transitions in nitrogen. In particular, we study the temperature dependence of the Raman bandwidths and frequency shifts of the Eg librational mode (zero pressure) and the internal modes of and (at various pressures) for the solid nitrogen by ...
Citation Formats
H. H. Yurtseven, “RAMAN-STUDY NH4C1 NEAR THE TRICRITICAL POINT,” JOURNAL OF MOLECULAR STRUCTURE, pp. 217–220, 1982, Accessed: 00, 2020. [Online]. Available: https://hdl.handle.net/11511/56613.