text: Atoms interacting via a sigma hole interactions are often closer than the sum of their van der waals radii. In addition, sigma hole interactions are also often associated with changes in the lengths and vibrational stretching frequencies of the covalent bond that gives rise to the sigma hole. Depending on the system engaging in the interaction, either a "blue shift", in which the bond contracts and the vibrational stretching frequency increases, or a "red shift", in which the bond lengthens and the vibrational stretching frequency decreases, is possible. The extent of these effects are related to the strength of the interaction, with stronger interactions tending to produce shorter interatomic distances between the interacting atoms and stronger red shifts.