Almost everyone has smelled the sharp, penetrating odor of ammonia, NH3. As the active product of "smelling salts," the compound can quickly revive the faint of heart and light of head. But more than a sniff of this toxic, reactive, and corrosive gas can make one very ill indeed. It can, in fact, be fatal. Ammonia is pretty nasty stuff. Nevertheless, it is also an extremely important bulk chemical widely used in fertilizers, plastics, and explosives (Goodwin, 2008, pp.96-105).
The melting and boiling points of ammonia, -77.7EC and -33.5EC, respectively, are both considerably higher than the corresponding properties of its chemical "cousins," PH3 and AsH3. This failure of NH3 to follow the usual trend of decreasing melting and boiling points with decreasing molecular weights indicates abnormally strong intermolecular attractions. The forces involved stem from hydrogen bonding, a consequence of the high electro negativity of nitrogen and the small size of the hydrogen atom (Grant, 2006, pp.562-584). The NH3 molecule has a large dipole moment, and this is consistent with its geometry, a triangular pyramid.
Aqueous Hydroxide Ions
The nature of the molecular-scale interactions between water molecules and H+ and OH- ions is one of the most fundamental issues in modern chemistry. Given that water can spontaneously dissociate into these two ions, it is not surprising that their behavior in liquid water is distinct from that of other ions (Jeffry, 2008, pp.970-982). For example, the mobility of hydroxide and hydrated protons in liquid water has long been recognized as being anomalously high,1 although considerable debate continues as to the underlying causes.2-19 Ab initio molecular dynamics (MD) methods have become particularly useful in the elucidation of the molecular-scale proton and OH- transport mechanisms, which have been shown to depend strongly on both the local solvation environment of the ions and the hydrogen bonding fluctuations of the water molecules (John, 1973, pp.47-94). However, despite these important computational advances, disagreement remains with regard to the proper description of OH- mobility in liquid water.6 It is therefore important to develop new experiments against which the theoretical results can be tested. To date, neutron diffraction studies of concentrated acid and base solutions have provided important insight into the microscopic structure of aqueous solvated H+ and OH-.10-15 Argon vibrational predissociation spectroscopy of OH-(H2O)m and H+(H2O)m clusters has elucidated some aspects of the fundamental ion-water ...