text: Infrared photodissociation (IRPD) spectroscopy uses infrared radiation to break bonds in, often ionic, molecules (photodissociation), within a mass spectrometer. In combination with post-ionization, this technique can also be used for neutral species. IRPD spectroscopy has been shown to use electron ionization, corona discharge, and electrospray ionization to obtain spectra of volatile and nonvolatile compounds. Ionized gases trapped in a mass spectrometer can be studied without the need of a solvent as in infrared spectroscopy.