The post-edge tail feature in the NH 3 (aq) spectrum has fewer features than those of water or NH + 4 (aq) and we have just established that it depends on continuum states that require many explicit water molecules to resolve. We attribute the long postedge tail to the free rotation of NH 3 about the C 3v axis and correlate it to the structureless region at and beyond the second hydration shell (> 5 Å) in the NH 3 (aq) radial distribution function (Fig. ). The more structured hydration behavior of water and NH + 4 (aq) result in post-edge tails that host more features, including a split post-edge peak in the case of water. Along the same vein, the results with only four explicit water molecules allow us to confidently assign the pre-edge and main-edge features to the immediately coordinating water molecules within the first hydration shell. In the case of ammonia, this means that the pre-and main-edge peaks are dominated by the coordination of NH 3 to just one water molecule, suggesting that these features can be reliably used as a direct probe of H-bonding in NH 3 (aq).