Facile Crystallization of Ice I_h via Formaldehyde Hydrate in Ultrahigh Vacuum under Cryogenic Conditions

Abstract

Although hexagonal ice (ice Ih) is the most common and highly studied crystalline form of ice, its nucleation from clathrate hydrates is poorly understood. Here, we report the formation of ice Ih through the dissociation of formaldehyde hydrate, prepared under ultrahigh vacuum (UHV) in the temperature window of 130–135 K. This unique route for crystallization is highly facile, and it occurs below the usual crystallization temperature of ice Ih of 155 K in UHV; the associated activation energy is also lower. Time-dependent reflection absorption infrared spectroscopy was used to detect the formaldehyde hydrate and to determine the crystallization kinetics of ice Ih. The dissociation of formaldehyde hydrate is found to be a diffusion-controlled process, which reduces the activation barrier of crystallization. This study provides evidence that formaldehyde hydrate can exist in extremely low (P, T) conditions without forming the geminal diol or its polymer in the presence of water. This new and facile route of crystallization in the context of interstellar environments may have implications for cometary and prebiotic science.

Rapid crystallization of amorphous solid water by porosity induction

“…The set-up has been used extensively to study molecular solids. 6,7,12,49,50 UHV was maintained by using several turbomolecular pumps backed by oil-free diaphragm pumps (Pfeiffer Vacuum). Pressure was monitored by a Bayard-Alpert gauge (Pfeiffer Vacuum), controlled by a MaxiGauge controller (Pfeiffer, Model TPG 256 A).…”

Microencapsulation ofCitrus aurantifoliaessential oil with the optimized CaCl2crosslinker and its antibacterial study for cosmetic textiles

“…Among all the microcapsules, the 15% crosslinkers was the optimum concentration to strengthen the shells rmly, thus holding the LO core up to 73%. Based on the Avrami equation, [44][45][46][47] the release rate constant of the microcapsules with 15% crosslinkers was the lowest one out of the others (Table 3). According to the computed n value of Avrami's equation, the LO release mechanism was ruled by the rst-order kinetics for all microcapsules.…”

Formation of Ethane Clathrate Hydrate in Ultrahigh Vacuum by Thermal Annealing

“…In UHV, CHs of acetone and formaldehyde were converted to cubic and hexagonal ices upon dissociation of the hydrate cages. 21,26 Also, it has been observed that ice XVI can be created by subjecting neon hydrate to pumping in a vacuum. 27 astrochemical environment.…”

“…Dissociation of these hydrates could lead to the formation of crystalline ice. In UHV, CHs of acetone and formaldehyde were converted to cubic and hexagonal ices upon dissociation of the hydrate cages. , Also, it has been observed that ice XVI can be created by subjecting neon hydrate to pumping in a vacuum . Physical properties such as density and refractive index of such ice forms may have important relevance for planetary objects.…”