Molecules with unusually strong coupling between electronic and vibrational states show intense infrared active bands. Using a porphyrin dimer radical cation as an example, we showed how infrared spectrum can be decomposed into orbital contributions, finding a strong coupling between the IRAVs and the singly occupied molecular orbital (SOMO), but also a significant effect of orbitals up to SOMO-3. Finally, we showed that the sensitivity of frontier orbital energies to nuclear movement can be used to identify IRAVs.