¹³C and ^33,34S isotope effects on the vapor pressure of liquid carbon disulfide

Abstract

GLBOR J A N C S~ and W. ALEXANDER VAN HOOK. Can. J. Chem. 55,3371 (1977). Prompted by the experimental investigation of Betts and Buchannon a thorough analysis of CS2 vapor pressure isotope effects has been made in the context of the theory of isotope effects in condensed phases and the available spectroscopic information. The agreement between the calculated and experimental results is satisfactory. The calculated results may be empirically described by the equations -0.529 In (PIICJIS2/PIJCJIS2) = + 0.00035 and The analysis indicates that the principal contribution to the 13C isotope effect is due to the shift on condensation of the asymmetric stretching frequency Av3, and quantitatively corroborates the theoretical conclusion reached earlier by Akopyan, Girin, and Bakshiev and others of the magnitude of the dielectric correction for this band. The 34S effects are principally determined by the hindered rotation and translation in the liquid and the shift in the symmetric stretching motion Av,. GABOR J A N C S~ et W. ALEXANDER VAN HOOK. Can. J. Chem. 55,3371 (1977).A la lumitre des rksultats expkrimentaux obtenus par Betts et Buchannon, on a fait une analyse compltte des effets isotopiques de la pression de vapeur du CS, en tenant compte de la thtorie des effets isotopiques en phase condenstes et des informations spectroscopiques disponibles. Les valeurs calculkes sont en bon accord avec les rksultats expkrimentaux. Les rksultats calculks peuvent Ctre empiriquement dtcrits par les kquations; L'analyse indique que la contribution principale a l'effet isotopique 13C est due au dtplacement sur la condensation de la frkquence assymetrique d'tlongation Av3 et confirme entierement la conclusion thkorique postulk antkrieurement par Akopyan, Girin et Bakshiev puis d'autres, sur I'ampleur de la correction diklectrique de cette bande. Les effets du 34S sont determines principalement par la rotation et la translation empCchke dans le liquide et par le dtplacement dans le mouvement d'klongation symktrique Av,.[Traduit par le journal]

Estimates of Dielectric Shifts in Infrared Spectra of Pure Liquids for Use in the Theoretical Evaluation of Vapor Pressure Isotope Effects

“…In a study of 13 C/ 12 C vapor pressure isotope effects in carbon disulfide, Jancso and Van Hook [3] found that, when the usual procedure is followed of deducing the isotope effect on the zero-point energy Reprint requests to Prof. M. Wolfsberg, Department of Chemistry, University of California, Irvine, California 92717, USA.…”

“…Thus, the observed spectroscopic fundamentals v max should be blue shifted by their respective dielectric shifts Av before the fundamentals are used for force constant calculations which in turn are used to calculate isotope effects on zeropoint energies in the condensed phase. This is just the procedure proposed by Jancsö and Van Hook [3]. Since dielectric shift values (Av L or zJv 0 ) are easily available for relatively few infrared absorptions.…”

“…Moreover, this quantity is frequently deduced from the observed fundamentals in the liquid phase and in the gas phase. Often the observed fundamentals are converted into appropriate force constants for liquid phase and gas phase molecules, and these force constants are then used to deduce isotope effects on the zero-point energy difference between the 3N-6 internal vibraional degrees of freedom in gas and in liquid.In a study of 13 C/ 12 C vapor pressure isotope effects in carbon disulfide, Jancso and Van Hook [3] found that, when the usual procedure is followed of deducing the isotope effect on the zero-point energy Reprint requests to Prof. M. Wolfsberg, …”