In this paper, we describe the formation of HD molecules in front of a graphite surface in the boundary layer of TEXTOR. The surface release of HD molecules was observed under different experimental conditions: in neutral beam experiments, in surface saturation experiments and in gas injection experiments. Molecular line emission of HD could be measured for the first time in a high temperature boundary plasma by means of Fulcher-α-band spectroscopy. The Q-branches of the first four diagonal bands were identified and analysed with respect to their rotational and vibrational population. No differences between isotopomers could be ascertained in the vibrational ground state population. Calibration spectra, which describe the isotope differences, as well as first experimental results with regard to the isotope exchange are shown. The main result is that HD molecules have to be included into the determination of the particle flux of recycled hydrogen isotopomers. By means of a model constructed on the chemical law of mass action, the release of the isotopomer H2, HD, and D2 can be described in the form of concentration ratios.