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PIPPARD RELATIONS MODIFIED FOR THE RAMAN FREQUENCY SHIFTS CLOSE TO I-II PHASE TRANSITION IN S-TRIAZINE

The pressure dependence of the frequency shifts 1/omega(partial derivative omega/partial derivative T)(P) is calculated from the 1/omega(partial derivative omega/partial derivative P)(T) for the Raman modes I and IV according to the spectroscopic modifications of the Pippard relations. The observed Raman frequencies of those modes are used for this calculation close to the I-II phase transition in s-triazine. From the frequency shifts, the isothermal compressibility kappa(T) and the specific heat C-P are also calculated as a function of pressure close to the I-II phase transition in s-triazine. Our calculated values of 1/omega(partial derivative omega/partial derivative T)(P) kappa(T) and C-P can be compared with the experimental measurements at various pressures in the phases I and II of s-triazine.