Infrared spectra of S-34 and C-13 isotopes of the OCS dimer are studied in the 2015-2075 cm(-1) region using a tunable laser to probe a pulsed supersonic expansion. The spectrum of ((OCS)-O-16-C-12-S-34)(2) is similar to that of the normal isotope, but that of ((OCS)-O-16-C-13-S-32)(2) differs due to nuclear spin statistics and due to small (< 0.01 cm(-1)) rotational perturbations whose nature is not entirely clear. The shift of the ((OCS)-O-16-C-13-S-32)(2) band origin relative to (OCS)-O-16-C-13-S-32 is significantly smaller than predicted by scaling from the normal isotope. It was not possible to detect spectra of isotopically mixed dimers. (c) 2007 Elsevier B.V. All rights reserved.