Electron detachment from doubly charged anions PtClxBr4-x2- to form PtClxBr4-x- (x=0-4) was probed for in a Fourier-transform ion-cyclotron-resonance mass spectrometer at 288 K. The corresponding decay rates were measured as a function of collision gas pressure. In the zero-pressure limit, nonzero unimolecular decay rate constants were observed for x=4 and 3 (0.273 +/-0.035 and 0.056 +/-0.019 s(-1) for 288 K, respectively). These show a strong temperature dependence suggesting the new phenomenon of blackbody radiation induced tunneling electron loss. Comparison to electron tunneling rates calculated by means of the Wentzel-Kramers-Brillouin approximation using Coulomb barrier properties and electron detachment energies derived from ab initio quantum chemical calculations provides a qualitative rationalization of the observed trends.