Mass Spectrometric Studies at High Temperatures. III. Dissociation Energies of the Alkaline Earth Monofluorides

Abstract

By heating the difluorides of magnesium, strontium, and barium under reducing conditions, one obtains significant amounts of the respective monofluorides. Mass spectrometric studies of equilibria involving these monofluorides have yielded the dissociation energies (D°298) 4.62±0.1 eV, 5.43±0.1 eV, and 5.83±0.1 eV for gaseous MgF, SrF, and BaF, respectively. These results support an ionic model for these molecules and are considerably higher than those previously accepted.

Mass spectrometric study of photoionization. XIII. Boron trichloride and diboron tetrachloride

“…Subtraction from the threshold energy of BC1+ results in /(BC1) = 10.20 ± 0.04 eV. Although considerably more reliable, this is remarkably close to the lesser of the values 10.2g and 10.60 eV obtained from electron impact data.7 The usual comparison with the ionization energies of isoelectronic molecules is favorable for SiO (10.8 ± 0.5 eV)18 and A1F (9.7 ± 0.5 eV) 19 but not for CS (11.7 eV).20 Nevertheless, the selected ionization process resulting in BC1+ and two atoms of chlorine is very probably correct. There is no evidence for the lower energy process yielding molecular chlorine.…”

Theoretical Dissociation Energies for Ionic Molecules

“…Our D 0 for BeF includes correlating the Be Is electrons, which produces a D 0 almost 0.1 eV greater than calculations in which the Is is not correlated. For MgF our D 0 of 4.66 eV lies between the two mass spectrometric determinations [48][49]. Since further basis set saturation is likely to increase our value slightly, we favor a value of 4.7±0.1 eV, which is consistent with all available values.…”

“…For SrF, our CI(SD) D 0 value agrees with all three experiments within their stated error bounds if one allows a 0.1 eV uncertainty in our value. However, our results again suggest that the flame photometry value [52] is too large and that the Ehlert et al [48] mass spectrometric determination is too low. We are in excellent agreement with the mass spectrometric determination of Hildenbrand (D 0 =5.62±0.07) [49], and would recommend adopting this value for SrF.…”

Gaussian basis sets for use in correlated molecular calculations. XI. Pseudopotential-based and all-electron relativistic basis sets for alkali metal (K–Fr) and alkaline earth (Ca–Ra) elements

“…At the QZ level, there is reasonably good agreement with available experimental data. [57][58][59][60][61][62][63][64][65][66][67][68][73][74][75][76][77] In the absence of experimental data for FrH and RaH, the present results can be compared to theoretical results of Koga et al, 22 which also used CCSD(T) with a DKH3 Hamiltonian. These NOSeC-CV-qzp results fall somewhere between the cc-pwCVTZ-DK and cc-pwCVQZ-DK values of the present work, suggesting that the NOSeC-CV sets also converge slowly towards the CBS limit, potentially overestimating r e and underestimating D e .…”