Ice crystal growth under the presence of krypton and methane at low temperature

To investigate the influence of foreign gas inclusion on the crystallization of ice, we studied the low-temperature (74 < T < 160 K) vacuum deposition of water molecules mixed with Kr or CH4 in a wide range of H2O/gas mixing ratios (0.004 < R < 4) by means of in-situ X-ray diffraction. When H2O vapor containing either Kr or CH4 was condensed onto a cold substrate, ice Ih crystals were found to grow below 130 K in a film of amorphous solid water (ASW), whereas pure H2O gas formed only ASW below 135 K. Small to moderate concentrations (R > 0.2) of Kr and CH4 enhance the formation of ice Ih and increase the crystal size, while at high foreign gas contents (R ⩽ 0.2) that may develop Kr or CH4 crystals below 92 K, the crystal size and relative amount of ice decrease strongly. The maximum ice Ih crystal size in the order of 200 nm was observed with either Kr or CH4 at 92 K for R = 0.2. We propose that Kr and CH4 induce the crystallization of ice by acting as a surfactant.