When we discuss molecular properties, we are usually referring to the
properties of a molecule when it is at equilibrium: i.e., when the
nuclei are in their minimum-energy configuration on the potential energy
surface. It is important to keep this in mind, since computational
chemistry programs often report properties (energy, dipole moment, etc)
for *any* geometry at which they are run. So, if you are trying to
report the equilibrium properties, you need to first *optimize* the
molecule to get the nuclei at the minimum on the PES. Only then should you
attempt to determine the equilibrium molecular properties. In particular,
be careful that you don't accidentally reset the geometry to the Hyperchem
``guess'' geometry by hitting ``Model Build'' after the geometry
optimization. If you do this, your results will all be for the wrong
geometry!

A special comment should be made about theoretically determined vibrational
frequencies. Every computational chemistry program defaults to predicting
the *harmonic* vibrational frequencies, which are the frequencies
determined from the second-derivative of the potential energy surface
according to the harmonic oscillator approximation:

(2) |

for each normal mode

That said, it is still sometimes possible to make correct comparisons between theory and experiment. One way is to compute the fundamental frequencies using theory. This is very involved and far beyond the scope of this lab. The other way is for experimentalists to do enough experiments to extract out the harmonic frequency. These are usually available for diatomic molecules and some polyatomic molecules. If experimentally deduced harmonic frequencies are available for your molecule, please report them. If not, please note that you have fundamental frequencies, and be aware that there will be a small discrepancy due to anharmonicity (often about 2-3%).