Condensation dynamics of cometary ice analogs in view of primordial accretion of volatiles on grain surfaces: A study through infrared spectroscopy

Binary and ternary gas mixtures of H2O, CO2, NH3 and CH4 were condensed at 10-6 mbar onto a KBr cold finger at 10 K. The composition of the few micrometre thick layers has been determined by infrared spectroscopy in transmission mode. The condensation dynamics together with the predominant matrix effect studied as a function of gas composition, deposition time and ice layer thickness reveal a lower condensation probability for the more volatile components CH4 and CO2 in mixtures of H2O-NH3-CH4 and H2O-NH3-CO2, respectively, with varying composition. The phenomena explain representative cases of early condensation and accretion processes of icy layers on interstellar grains.