Evaluation of the exothermicity of the chemi-ionization reaction Sm + O → SmO+ + e-
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 ≤ D0(Sm+-O) ≤ 6.500 eV. A more precise value is measured to be 5.725 ± 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, ∼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 D0(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.
Journal of Chemical Physics
Digital Object Identifier (DOI)
Cox, Kim, J., Armentrout, P. B., Bartlett, J., VanGundy, R. A., Heaven, M. C., Ard, S. G., Melko, J. J., Shuman, N. S., & Viggiano, A. A. (2015). Evaluation of the exothermicity of the chemi-ionization reaction Sm + O → SmO++ e. The Journal of Chemical Physics, 142(13), 134307–134307. https://doi.org/10.1063/1.4916396