Role of photoionization and photochemistry in ionization processes of organic molecules and relevance for matrix‐assisted laser desorption lonization mass spectrometry

The ionization in ultraviolet laser desorption was investigated for a large number of small polar organic molecules which have a strong resonance absorption at the laser wavelength. In many cases, both positive‐ and/or negative‐ion mass spectra show strong signals of ion species which deviate from the simple scheme of even‐electron quasimolecular and fragment ion formation commonly expected for desorption techniques. These are radical cations...