For platinum (Pt) doped silicon samples co-doped with hydrogen (1H) and deuterium (2H) the principal g values of the ESR signal of the Pt2H pair were found to significantly differ from that of the Pt1H pair, signifying the presence of an isotopic shift for the g-tensor. In similar samples, energy level positions of the PtH pair and the PtH3 complex were determined from the results of photo-ESR studies. Two energy levels of the PtH pair were found to be positioned at EC-0.47 eV and EV+0.56 eV. The energy level of the PtH3 complex was found to be positioned at EC-0.73 eV.