Investigation of the Ice–Water Vapor Equilibrium Along the Sublimation Line

An accurate knowledge of the thermodynamic properties of water at low temperature plays an important role in atmospheric processes, chemical physics, and metrological applications. Preliminary investigations of the water vapor-ice equilibrium along the sublimation line have been carried out at Istituto Nazionale di Ricerca Metrologica (INRIM). The measurements covered the temperature range from -50 degrees C to 0 degrees C, corresponding to a saturation vapor pressure from about 4 Pa to 611 Pa. The measurements were performed using a small gold-plated cell kept in a liquid bath at a constant temperature with millikelvin stability. The sample cell was connected to a manifold where the pressure was measured using two capacitive diaphragm pressure gauges. The paper reports the water sample preparation, measuring method, and measurement corrections. Measurement results are discussed and uncertainty sources estimated. The resulting expanded relative uncertainty (k = 2) varies from 0.038 % at 0 degrees C to 0.70 % at -50 degrees C.