Study of the Isotopic Disproportionation Reaction between Light and Heavy Water Using a Pulsed-Molecular-Beam Mass Spectrometer

Abstract

Isotopic exchange equilibrium in the disproportionation reaction H2O+D2O=2 HDO was studied at 0° and 25° and over a range of deuterium compositions using a pulsed-molecular-beam mass spectrometer. The equilibrium constant K was found to be 3.75±0.07 at both temperatures. The pulsed-beam mass spectrometer was shown to be effective in minimizing the ``memory effect'' in the mass spectrometer. The experimental K is shown to be consistent with equilibrium constants for similar isotopic disproportionation reactions and with current theory.

Mass spectrometric separation and quantitation of overlapping isotopologues. H2O/HOD/D2O and H2Se/HDSe/D2Se mixtures

“…The two most recent liquid phase equilibrium constant measurements (at 298 K) are 3.86 Ϯ 0.07 [3] and 3.86 Ϯ 0.01 [27] [23] difference between liquid and gas-phase equilibrium constants is estimated to be only 0.03 [28]. Previous direct mass spectrometric measurements (carried out in the 1960s) have led to the values of K ϭ 3.75 Ϯ 0.07 [29] and 3.76 Ϯ 0.02 [26]; however, these measurements have been performed at electron accelerating voltages from 3 eV (H 2 O) [25] Se concentrations in the headspace. The resulting mixtures were then analyzed using GC/MS, and their composite mass spectra were decomposed using the weighted two band-target entropy minimization algorithm and the statistical model.…”

On the proper use of the Bigeleisen–Mayer equation and corrections to it in the calculation of isotopic fractionation equilibrium constants

“…For the water vapor internal equilibrium reaction: H 2 O + D 2 O = 2HDO, large deviations were found between theoretical studies and experiments (Pyper et al, 1967;Pyper and Newbury, 1970;Pyper and Christensen, 1975). Wolfsberg (1969) showed that it was not sufficiently accurate to add anharmonic corrections without the contributions of G 0 terms to partition function ratios.…”

Hydrogen—deuterium exchange in water vapor: The mass spectrometric sensitivities and the equilibrium constant

“…[5] but disagree with those in Refs. [1][2][3][4], (See Table 1 The iteration computer code also calculated the sensitivity ratio, S., at seven different times. The ratios are shown in Table 5.…”

“…[1][2][3][4] and recent theoretical calculations[6-3j of K » 3.85 at 25*C might be the result of a value of S different from unity. The meastEreaetU of the sensitivities of isotoplc species of water Is complicated by the phenomenon known as taenory effect.…”

“…The equilibrium constant, *StI)n» f°r the gas phase reaction* H.,0 + l)7 <> -21IIJO (2) can be expressed as,…”