This is the start window of MolVib showing the commands available. This DOS/WIN application in Turbo Pascal 7.0 has been translated from Dr. Daniel Huber's Mac program. It originated during his thesis work with me at the Univ. of Bern and was further developed while Huber worked at the University of Seattle.- After input of the nuclear masses, the connectivity of the atoms, and the force constants, the program solves the vibrational eigenvalue problem and generates the spectrum in the normal mode space. Command 3 allows to see an animation of the nuclear motions in every normal mode. Command 8 offers the superposition of two normal modes with arbitrary phase and mixing coefficients. The next figure is a (still!) example of this feature.

Few chemists know something about the skeleton motions of their molecules because those do not normally show distinctive features of group vibrations useful for analytic or structural information. However, they are very important thermodynamically because they carry most of the vibrational energy near 300 K.- Here is the superposition of the two normal modes of highest energy of the C6-ring of cyclo-hexane. Because they are degenerate the vibrational angular momentum is a constant of the motion. The nuclear displacements at this moment are the distances between the C's and the center of the nearest circles. The equilibrium, vibrationless, structure is given by the projection of the six C.