Intramolecular vibrational energy redistribution

Intramolecular vibrational energy redistribution (IVR) is a phenomenon in molecular dynamics where energy absorbed by a molecule during vibrational excitation is redistributed among the various vibrational modes of that molecule. In a molecule, there are typically many vibrational modes corresponding to different ways the atoms can move relative to each other (e.g., stretching, bending, twisting). When a molecule absorbs energy, for example through a photon in infrared spectroscopy, that energy initially excites a specific vibrational mode.