Critical behaviour of the thermodynamic quantities close to phase transitions in molecular crystals using raman data

---

Tezin Türü: Doktora

Tezin Yürütüldüğü Kurum: Orta Doğu Teknik Üniversitesi, Fen Edebiyat Fakültesi, Fizik Bölümü, Türkiye

Tezin Onay Tarihi: 2017

Öğrenci: HİLAL ÖZDEMİR

Danışman: HASAN HAMİT YURTSEVEN

Özet:

In this thesis we investigate the pressure and temperature dependence of the Raman frequencies for diffirent modes of benzene at ambient conditions (P=0 GPa and T=300 K). By using the experimental data we calculated the volume and frequency as a function of pressure at constant temperature and as a function of temperature at constant pressure, thus isothermal and isobaric mode Grüneisen parameter has been inferred in the diffrent modes. Our calculations show that calculated Raman frequencies agree well with the observed data for each mode in solid benzene. In a more generalized way, Raman frequencies were calculated as a function of pressure and temperature for different modes of solid naphthalene and anthracene. Our calculations are in a good agreement with the observed data. Thermodynamic quantities such as heat capacity Cp, entropy S was analyzed using the experimental data at various temperatures and pressures through the Raman frequencies and crystal volume for the different modes in solid benzene, naphthalene and anthracene. Our results agree better with the observed data at higher pressures and temperatures. Also, quasi-harmonic approximation is used to calculate thermodynamic quantities for solid benzene, naphthalene and anthracene. Quasi-harmonic vibrational energy is defined as a function of temperature to originate of deriving other thermodynamic quantities of solid benzene, naphthalene and anthracene. When the experimental data is avalaible our calculations through the quasi-harmonic vibrational energy can be compared with the observed data for solid benzene, naphthalene and anthracene.