title: Second-order correction to the Bigeleisen-Mayer equation due to the nuclear field shift.
abstract: The nuclear field shift affects the electronic, rotational, and vibrational energies of polyatomic molecules. The theory of the shifts in molecular spectra has been studied by Schlembach and Tiemann [Schlembach, J. & Tiemann, E. (1982) Chem. Phys. 68, 21]; measurements of the electronic and rotational shifts of the diatomic halides of Pb and Tl have been made by Tiemann et al. [Tiemann, E., Knöckel, H. & Schlembach, J. (1982) Ber. Bunsenges. Phys. Chem. 86, 821]. These authors have estimated the relative shifts in the harmonic frequencies of these compounds due to the nuclear field shift to be of the order of 10(-6). I have used this estimate of the relative shift in vibrational frequency to calculate the correction to the harmonic oscillator approximation to the isotopic reduced partition-function ratio (208)Pb(32)S/(207)Pb(32)S. The correction is 0.3% of the harmonic oscillator value at 300 K. In the absence of compelling evidence to the contrary, it suffices to calculate the nuclear field effect on the total isotopic partition-function ratio from its shift of the electronic zero point energy and the unperturbed molecular vibration.
authors.affiliation: Department of Chemistry, State University of New York at Stony Brook, Stony Brook, NY 11794-3400, USA.
authors.forename: J
authors.initials: J
authors.lastname: Bigeleisen
mesh_terms: D055598:Chemical Phenomena; D002627:Chemistry, Physical; D007554:Isotopes; D007854:Lead / Q000737:chemistry*; D008433:Mathematics; D013057:Spectrum Analysis; D013440:Sulfides / Q000737:chemistry*
chemical_list: D007554:Isotopes; D013440:Sulfides; C018391:lead sulfide; D007854:Lead