Diffraction Pattern and Structure of Liquid Trimethylamine Decahydrate at 5°C

The scattering of x rays from a solution of trimethylamine in water having the same composition as the solid clathrate hydrate has been measured and analyzed at the melting point of the crystal. Two independent sets of small‐ and large‐angle data were collected and combined into one; the resulting diffraction pattern covers an angular range ${\text{0.02\hspace{0.17em}≤\hspace{0.17em}s\hspace{0.17em}≤\hspace{0.17em}16 Å}}^{\text{−1}}$ not previously reported for any liquid. Correlation functions for the solution and for pure water are very similar in the region of intermolecular distances $\text{r\hspace{0.17em}>\hspace{0.17em}2.5 Å}$ , and the absence of interference maxima in the small‐angle portion of the intensity functions precludes any significant deviation of the pair density from the uniform bulk density beyond approximately 8 Å; in other words, there is no “structure” beyond this distance. The x‐ray data provide strong evidence for the existence of a three‐dimensional network in the solution. Intensity and radial distribution functions have been calculated for two specific structural models. The average short‐range order in the solution is explained equally well by either of the two models.