NH₃ as unique non-classical content-former within clathrate hydrates

High quality FTIR spectra of aerosols of NH₃-THF and NH₃-TMO binary clathrate hydrates (CHs) have been measured. Our recently developed all-vapor sub-second approach to clathrate-hydrate formation combined with computational studies has been used to identify vibrational spectroscopic signatures of NH₃ within the gas hydrates. The present study shows that there are three distinct NH₃ types, namely, classical small-cage NH₃, nonclassical small-cage NH₃, and NH₃ within the hydrate network. The network ammonia does not directly trigger the non-classical CH structure. Rather, the ammonia within the network structure perturbs the water bonding, introducing orientational defects that are stabilized by small and/or large cage guest molecules through H-bonding. This unusual behavior of NH₃ within CHs opens a possibility for catalytic action of NH₃ during CH-formation. Furthermore, impacts over time of the small-cage NH₃-replacement molecules CO₂ and CH₄ on the structure and composition of the ternary CHs have been noted.