This study gives an evidence for the validity of our spectroscopic modification of the Pippard relation as apphed to ammonia solid I close to the melting point. We use our calculated frequencies for the rotatory lattice (librational) mode in ammonia solid I for the pressures of 0, 1.93 and 3.07 kbars. We obtain that the specific heat C-p varies linearly with the frequency shifts 1/v(delta v/delta T)(p) for this Raman mode at those pressures studied in this crystalline system. Our values of the slope dP(m)/dT that we deduced from the linear plots, are not in satisfactory agreement with the experimental values in ammonia solid I near the melting point. (c) 2005 Elsevier Ltd. All rights reserved.