Direct measure of the hydration number of aqueous methane.

A hydration number of 20 has been measured for aqueous CH4 in the temperature range 273-298 K on the basis of the simultaneous observation of the 13C isotropic resonance lines of CH4 in both aqueous solution and the dodecahedral cage of CH4 structure I hydrate. Additional experimental evidence and analysis reported in this paper suggest that the dominant aqueous hydration number of methane is 20.