Calculation of the Raman frequencies using volume data close to the tricritical and second order phase transitions in NH4Cl

YURTSEVEN H. H., Kavruk D.

JOURNAL OF MOLECULAR STRUCTURE, vol.924, pp.544-547, 2009 (SCI-Expanded) identifier identifier

  • Publication Type: Article / Article
  • Volume: 924
  • Publication Date: 2009
  • Doi Number: 10.1016/j.molstruc.2008.10.069
  • Journal Name: JOURNAL OF MOLECULAR STRUCTURE
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Page Numbers: pp.544-547
  • Middle East Technical University Affiliated: Yes

Abstract

We calculate here the Raman frequencies of the v(5) TO(174 cm(-1)) and v(2) (1708 cm(-1)) modes as a function of temperature in the region of the tricritical (P = 1.6 kbar) and the second order (P = 2.8 kbar) phase transitions in NH4Cl. This calculation of the Raman frequencies is performed through the mode Gruneisen parameter by using the experimental length-change data obtained at zero pressure where the NH4Cl crystal exhibits a weakly first order phase transition (T-lambda = 242 K). The predicted Raman frequencies of the modes studied here, agree with our observed frequencies for the tricritical (T-c = 257 K) and second order (T-c = 268 K) transitions in NH4Cl.