Mid-infrared FTIR spectra of argon matrix isolated selenoketene-d(0) and selenoketene-d(1) have been recorded. These transient species were prepared by flow thermolysis of the corresponding 1,2,3-thiadiazoles. With the aid of ab initio predictions of the vibrational frequencies and intensities, six of the nine fundamentals have been identified for each isotopomer. The spectra are dominated by a very intense C-C stretching band; the other fundamentals are significantly weaker and more difficult to assign.