The v(1) spectra of (OC)-O-16-C-12-DI and O-16(12) C-ID, as well as v2 of (OC)-O-16-C-12-01, (OC)-O-16-C-12-ID have been recorded using a quantum cascade laser pulsed slit supersonic jet spectrometer. Intensity measurements made simultaneously in the same expansion for transitions in v(2) (OC)-O-16-C-12-HI: (OC)-O-16-C-12-IH and v1 (OC)-O-16-C-12-01: (OC)-O-16-C-12- ID isomers permit determination of the isomerization for the former pair to be +2.8(1.0) and the latter 6.0(1.0) cm(-1). These results confirm prediction of ground state deuterium isotopic isomerization made using a generated morphed potential. Further analyses indicate OC.HI is a prototype for complexities associated with isomerization and isotopic effects in excited stretching vibrations. (C) 2014 Elsevier B.V. All rights reserved.