Evaluation of the exothermicity of the chemi-ionization reaction Sm plus O - SmO+ + e(-)

摘要

The exothermicity of the chemi-ionization reaction Sm + O -> SmO+ + e(-) has been re-evaluated through the combination of several experimental methods. The thermal reactivity (300-650 K) of Sm+ and SmO+ with a range of species measured using a selected ion flow tube-mass spectrometer apparatus is reported and provides limits for the bond strength of SmO+, 5.661 eV <= D-0(Sm+-O) <= 6.500 eV. A more precise value is measured to be 5.72(5) +/- 0.07 eV, bracketed by the observed reactivity of Sm+ and SmO+ with several species using a guided ion beam tandem mass spectrometer (GIBMS). Combined with the established Sm ionization energy (IE), this value indicates an exothermicity of the title reaction of 0.08 +/- 0.07 eV, similar to 0.2 eV smaller than previous determinations. In addition, the ionization energy of SmO has been measured by resonantly enhanced two-photon ionization and pulsed-field ionization zero kinetic energy photoelectron spectroscopy to be 5.7427 +/- 0.0006 eV, significantly higher than the literature value. Combined with literature bond energies of SmO, this value indicates an exothermicity of the title reaction of 0.14 +/- 0.17 eV, independent from and in agreement with the GIBMS result presented here. The evaluated thermochemistry also suggests that D-0(SmO) = 5.83 +/- 0.07 eV, consistent with but more precise than the literature values. Implications of these results for interpretation of chemical release experiments in the thermosphere are discussed. (C) 2015 AIP Publishing LLC.