A method for studying dissociation of diatomic molecules by isotope spectroscopy is presented both theoretically and practically. A theory based on combinatorial analysis is presented for molecules of the form 132 and BC. Molecular dissociation rates can be calculated from measurements of isotope exchange provided the isotopes in the molecules can be considered as chemically equivalent. Dissociation measurements Of O-2 on Pt, RuO2, Ir and Ni-Zr-Sm as well as CO on Pt and Al are presented in the temperature range 400-900 degreesC. (C) 2002 Elsevier Science B.V. All rights reserved.