Dissociation Energies of Group IIIA Monofluorides—The Possibility of Potential Maxima in Their Excited Π States

The dissociation energies D0″ have been measured for GaF, InF, and TlF using high-temperature mass-spectrometric techniques. These results, along with those from previous studies, yield D0″=180±3, 159±3, 138±3.5, 121±3.5, and 101±3.5 kcal/mole for BF, AlF, GaF, InF, and TlF, respectively. Comparison of D0″ thus obtained with that derived from Birge—Sponer extrapolation of the A 1Π state indicates that for all these molecules the spectroscopically derived dissociation energies are higher than the thermochemical values. It is suggested that the difference may be due to a potential maximum in the A 1Π states BF, AlF, GaF, and InF. A maximum is also suggested for the a 3Π1 state of TlF. The appearance potentials of these monofluorides were measured and were found to be 11.5±0.4, 9.5±0.5, 10.6±0.4, 9.6±0.5, and 11.2±0.5 eV for BF+, AlF+, GaF+, InF+, and TlF+, respectively. The dissociation energies and the appearance potentials are briefly discussed in terms of the molecular states of the respective molecules.