Photoionization of High-Temperature Vapors. IV. TlF, TlCl, and TlBr

The vapors of TlF, TlCl, and TlBr have been studied by photoionization mass spectrometry. From the thresholds for formation of Tl⁺, the dissociation energies obtained are 4.57 ± 0.02, 3.82 ± 0.02, and 3.42 ± 0.02 eV for TlF, TlCl, and TlBr, respectively. The TlF value provides confirmation for the existence of barriers in the potential energy curves of its ${}^3{\pi }_0^{+}$ and ${}^3{\pi }_1$ states. The ion pairs in TlF and TlCl are formed with considerable kinetic energy, probably by a predissociative mechanism.