Stability of the Gaseous Ammonium Chloride Molecule

Abstract

The equilibrium vapor effusing from a Knudsen cell, in which solid ND4Cl was evaporated, was analyzed by a quadrupolemass spectrometer. In the temperature range considered (335°–485°K) the main vaporization process corresponds to the decomposition of the solid towards gaseous ND3 and DCl; the measured enthalpy change Δ H ° 407 dec [ ND 4 Cl ( s )] = 42.6 ± 2.0 kcal mole −1 is very close to that measured for NH4Cl: Δ H ° 407 dec [ NH 4 Cl ( s )] = 42.5 kcal mole −1 . Apart from the main gaseous species, small proportions (5 × 10−5–2 × 10−3) of ND4Cl molecules were also observed. The ND4Cl molecule fragments (> 99%) under electron impact and yields the ND 4 + (m / e = 22) ion. From the observed ion intensity ratios, as well as their dependence on temperature, D 0 °( NH 4 Cl ⇋ NH 3 + HCl) = 10.0 ± 3.0 kcal mole −1 was obtained confirming Clementi's computed prediction < 14.0 kcal mole−1.