title: Evaluation of the exothermicity of the chemi-ionization reaction Sm + O → SmO(+) + e(.).
abstract: 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.
authors: Department of Chemistry, University of Utah, Salt Lake City, Utah 84112, USA.
authors: Richard M
authors: RM
authors: Cox
authors: Department of Chemistry, University of Utah, Salt Lake City, Utah 84112, USA.
authors: JungSoo
authors: J
authors: Kim
authors: Department of Chemistry, University of Utah, Salt Lake City, Utah 84112, USA.
authors: P B
authors: PB
authors: Armentrout
authors: Department of Chemistry, Emory University, Atlanta, Georgia 30322, USA.
authors: Joshua
authors: J
authors: Bartlett
authors: Department of Chemistry, Emory University, Atlanta, Georgia 30322, USA.
authors: Robert A
authors: RA
authors: VanGundy
authors: Department of Chemistry, Emory University, Atlanta, Georgia 30322, USA.
authors: Michael C
authors: MC
authors: Heaven
authors: Air Force Research Laboratory, Space Vehicles Directorate, Kirtland AFB, Albuquerque, New Mexico 87117, USA.
authors: Shaun G
authors: SG
authors: Ard
authors: Department of Chemistry, University of North Florida, Jacksonville, Florida 32224, USA.
authors: Joshua J
authors: JJ
authors: Melko
authors: Air Force Research Laboratory, Space Vehicles Directorate, Kirtland AFB, Albuquerque, New Mexico 87117, USA.
authors: Nicholas S
authors: NS
authors: Shuman
authors: Air Force Research Laboratory, Space Vehicles Directorate, Kirtland AFB, Albuquerque, New Mexico 87117, USA.
authors: Albert A
authors: AA
authors: Viggiano