We examine here our spectroscopic modification of the Pippard relation which is a linear variation of the thermal expansivity alpha(p) with the frequency shifts (1/nu)(partial derivative nu/partial derivative p)(T) close to the melting point in ammonia solid II. For this we use our calculated frequencies for the Raman mode of nu (51 cm(-1)) in ammonia solid II for the pressures of 3.65, 5.02 and 6.57 kbars. We establish this linearity between alpha(p) and (I/nu)(partial derivative nu/partial derivative(p))(T) for the pressures studied in ammonia solid II close to the melting point. The observed behaviour of ammonia solid II is explained in terms of our spectroscopic relation given here. (C) 2007 Elsevier B.V. All rights reserved.