The photolysis of a series of substituted benzenediazonium salts was studied by low-temperature and time-resolved spectral methods and by analysis of products formed in alcohol solutions at room temperature. The spin multiplicity of the ground state aryl cations formed by nitrogen loss from the diazonium salt is known to depend on the nature of the substituent. The low-temperature spectroscopic experiments confirm a triplet ground state when the cation contains a p-amino group. These triplet cations are detected directly in fluid solution for the first time, and their lifetimes are estimated. Analysis of products reveals that these cations react predominantly from the initially formed singlet state rather than theirtriplet ground state.