Mixing Effects in the Crystallization of Supercooled Quantum Binary Liquids

By means of Raman spectroscopy of liquid microjets we have investigated the crystallization process of supercooled quantum liquid mixtures composed of parahydrogen (pH$_2$) diluted with small amounts of up to 5\% of either neon or orthodeuterium (oD$_2$), and of oD$_2$ diluted with either Ne or pH$_2$. We show that the introduction of Ne impurities affects the crystallization kinetics in both the pH$_2$-Ne and oD$_2$-Ne mixtures in terms of a significant reduction of the crystal growth rate, similarly to what found in our previous work on supercooled pH$_2$-oD$_2$ liquid mixtures [M. K\"uhnel et {\it al.}, Phys. Rev. B \textbf{89}, 180506(R) (2014)]. Our experimental results, in combination with path-integral simulations of the supercooled liquid mixtures, suggest in particular a correlation between the measured growth rates and the ratio of the effective particle sizes originating from quantum delocalization effects. We further show that the crystalline structure of the mixture is also affected to a large extent by the presence of the Ne impurities, which likely initiate the freezing process through the formation of Ne crystallites.Comment: 19 pages, 7 figures, submitted to J. Chem. Phy

Infrared-active vibron bands associated with rare gas atom dopants isolated in solid parahydrogen

We report high-resolution infrared absorption spectroscopic studies of the dopant-induced Q₁(0) vibron band in solid parahydrogen crystals doped with low concentrations of rare gas atoms. The frequency, lineshape, and integrated absorption coefficient for the rare gas atom-induced Q₁(0) vibron band are measured for Ne, Ar, Kr, and Xe. The observed lineshapes and peak maxima frequencies are sensitive to the H₂ vibrational dependence of the dopant-H₂ isotropic intermolecular potential. Trends observed for Ar, Kr and Xe indicate the vibrational dependence is strong enough for Xe to trap the infrared-active vibron in its first solvation shell while for Ar the vibron remains delocalized. The Ne-induced feature displays a qualitatively different lineshape which is attributed to the weak intramolecular vibrational dependence of the Ne–H₂ intermolecular potential relative to the H₂–H₂ interaction. The lineshapes of the Ar, Kr, and Xe dopant-induced Q₁(0) pure vibrational features agree well with recent first principles calculations