 We obtain a basis for the internal space by defining 3"N"-6 linearly independent vectors
The vectors formula_20 could be Wilson's s-vectors or could be obtained in the harmonic approximation by diagonalizing the Hessian of "V".We next introduce internal (vibrational) modes,
The physical meaning of "q"r depends on the vectors formula_20.For instance, "q"r could be a symmetric stretching mode, in which two C—H bonds are simultaneously stretched and contracted.