Revisit to Vapor Pressure Isotope Effects of Water Studied by Molecular Orbital Calculations

Abstract

H/D and ¹⁶O/¹⁸O vapor pressure isotope effects (vpies) of water between liquid water and water vapor were reinvestigated by estimating the reduced partition function ratios, rpfrs, of water clusters, (H₂O)n, with n up to 100 at the HF/6-31G(d) level of molecular orbital theory. Large water clusters with n = 80−100 resulted in a reasonable estimate of the ¹⁶O/¹⁸O vpie, which was in contrast to the one for which only small water clusters had been considered. Contrary to this, no appreciable improvement in the H/D vpie reproduction by using large water clusters was observed.

KEYWORDS:

• vapor pressure isotope effects
• reduced partition function ratio
• water
• water clusters
• fractionation factor
• molecular orbital calculations
• HF/6-31G(d)