This advanced undergraduate chemistry laboratory exercise takes advantage of the unique spectroscopic properties of the free radical chlorine dioxide to allow for a direct comparison of its symmetric stretch in both the ground and excited states. It incorporates several subject areas covered in an undergraduate chemistry degree (synthesis, spectroscopy, and computational chemistry) and is suitable for an advanced level inorganic, physical, or integrated chemistry laboratory course. Students synthesize aqueous chlorine dioxide, analyze a vibronic progression of the symmetric stretch in the excited state using UV-vis spectroscopy, and also record the energy of the symmetric stretch in the ground state using Raman spectroscopy. In addition to offering advanced undergraduate students the opportunity to study the chemistry of a radical first-hand, this exercise also reinforces the use of synthetic techniques for the purpose of studying how a molecule's physical properties vary with the electronic state. An optional computational chemistry component includes optimizing the geometries of the ground and excited states of the radical, calculating the charge, and comparing computed harmonic vibrational frequencies to the experimental data.