“…Although the evaluation of RFPR's from the vibrational frequencies is straightforward, it presents an additional step, which may have discouraged some researchers from pursuing the topic. Since the RFPR approach also relies upon the Teller-Redlich product rule (given in Teller's personal communication to Angus et al (1936); see Wilson, Decius and Cross, 1955 for a more modern derivation and applications) it makes it difficult to separate vibrational, rotational and translational contributions or to separate enthalpic and entropic contributions to the free energy. It is also based on the harmonic oscillator approximation, which may not be adequate in all cases.…”