Ammonia
Introduction
Although the ammonia molecule (NH3) is a small and very simple molecule, it is also very interesting. In the first part of this lab you are going to carry out some calculations on NH3.Ammonia is a colorless gas under standard conditions, with a sharp, acrid odor. Under 1 atm, it boils at -33.4 °C and because it can be liquefied at room temperature it often used as a coolant. Ammonia is also highly soluble in water, and under standard conditions, a saturated solution is about 30% ammonia. The solution is a powerful cleaning agent, and a little added to your window-cleaning solution not only cleans but also helps prevents streaking. Nitrogen is an essential element for plant growth, but plants cannot use elemental nitrogen directly from the atmosphere, N2. Nitrogen is often added to fertilizers as ammonia ("anhydrous ammonia"), or as ammonium compounds, soil bacteria then convert it to nitrite, NO2-, which is then oxidized to nitrate and absorbed by the plants. Many salts are formed with the ammonium ion NH4+. Smelling salts is ammonium carbonate, (NH4)2CO3, which decomposes readily into ammonia (which provides the strong smell), water and carbon dioxide. Ammonium ions when combined with aromatic organic cations form a new class of liquids called "ionic liquids" because they are made of ions but unlike NaCl, which melts at about 800 °C, these substances remain liquid at temperatures under 100 °C.
A low potential barrier exists between two the inverted structures of ammonia, this processes is achieved by the hydrogen atoms quantum tunnelling from one side of the nitrogen atom to the other. This purely quantum phenomenon causes "inversion doubling" of the vibrational modes of ammonia. The ammonia MASER uses these levels to achieve (coherent) laser like light in the microwave region. Another use of these purely quantum mechanical levels is in quantum computing. The ammonium molecule can thus be used as a "qubit" (a quantum information unit). If we say the state on the left of the diagram above is the "left" state, and the state on the right of the diagram above is the "right" state. Then the ammonia molecule flips between these two states many times a second. However a linear combination of these two states forms a "stationary state" (a state that does not change over time, and hence the word stationary!). The two physical states form "+" and "-" stationary states (which are eigenvectors of the system Hamiltonian). A quantum computer will force a change from one state to the other (by applying "light" of the right resonant frequency). This is equivalent to the 0 and 1 of ordinary electron based computing.
Activities
In the introductory sessions you were introduced into how to set-up and run a calculation. This section extends on this by using information you are going calculate to understand more about the inversion processes of ammonia. It follows roughly the same sequence of calculations as you carried out for BH3.