High-resolution energy-selected study of the reaction NH3+ -> NH2 ++H: Accurate thermo chemistry for the NH2/NH2+ and NH3/NH3 + systems

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Employing the newly developed high-resolution pulsed field ionization-photoelectron (PFI-PE)-photoion coincidence (PFI-PEPICO) technique, we have examined the dissociation of energy-selected NH{sub 3}{sup +} to form NH{sub 2}{sup +} + H near its threshold. The breakdown curves for NH{sub 2}{sup +} and NH{sub 3}{sup +} thus obtained yield a value of 15.765 {+-} 0.001 eV for the 0 K dissociation threshold or appearance energy (AE) for NH{sub 2}{sup +} from NH{sub 3}. This value, together with the known ionization energy (IE=10.1864 {+-} 0.0001 eV) and 0 K bond dissociation energy (D{sub 0} = 4.6017 {+-} 0.0025 eV) for NH{sub 3}, allows the ... continued below

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Song, Y.; Qian, X.M.; Lau, K.C.; Ng, C.Y.; Liu, J.B. & Chen, W.W. March 1, 2001.

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Employing the newly developed high-resolution pulsed field ionization-photoelectron (PFI-PE)-photoion coincidence (PFI-PEPICO) technique, we have examined the dissociation of energy-selected NH{sub 3}{sup +} to form NH{sub 2}{sup +} + H near its threshold. The breakdown curves for NH{sub 2}{sup +} and NH{sub 3}{sup +} thus obtained yield a value of 15.765 {+-} 0.001 eV for the 0 K dissociation threshold or appearance energy (AE) for NH{sub 2}{sup +} from NH{sub 3}. This value, together with the known ionization energy (IE=10.1864 {+-} 0.0001 eV) and 0 K bond dissociation energy (D{sub 0} = 4.6017 {+-} 0.0025 eV) for NH{sub 3}, allows the determination of the D{sub 0}(NH{sub 2}{sup +}-H) and IE(NH{sub 2}), which are 5.5786 {+-} 0.0010 and 11.1633 {+-} 0.0025 eV, respectively. Using the known 0 K heats of formation ({Delta}H{sup 0}{sub f0}) for NH{sub 3} and H and the AE(NH{sub 2}{sup +}), we obtain the {Delta}H{sup o}{sub f0}(NH{sub 2}{sup +}) = 302.60 {+-} 0.08 kcal/mol. The PFI-PE spectrum for NH{sub 3} exhibits a step-like feature at the 0 K AE(NH{sub 2}{sup +}), indicating that the dissociation of excited NH{sub 3} in high-n (n {ge} 100) Rydberg states at energies slightly above the dissociation threshold occurs on a time scale {le}10{sup -7} s. This step confirms the AE(NH{sub 2}{sup +}) value derived from the PFI-PEPICO measurements. Highly accurate energetic data with well-founded error limits, such as those obtained in the present and other studies using the PFI techniques, are expected to play an important role for the development of the next generation of ab initio quantum computation procedures. This experiment has stimulated a state-of-the-art ab initio quantum chemical calculation (Dixon et al., J. Chem. Phys., accepted). The comparison between theoretical predictions and the best experimental results for the NH{sub 2}/NH{sub 2}{sup +} and NH{sub 3}/NH{sub 3}{sup +} systems indicates that the accuracy of the computational scheme used is {le}0.4 kcal/mol.

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  • Other Information: Journal Publication Date: August 8 2001

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  • Report No.: LBNL--48265
  • Report No.: none
  • Report No.: LBNL/ALS--43635
  • Grant Number: AC03-76SF00098
  • Office of Scientific & Technical Information Report Number: 842956
  • Archival Resource Key: ark:/67531/metadc782136

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Office of Scientific & Technical Information Technical Reports

Reports, articles and other documents harvested from the Office of Scientific and Technical Information.

Office of Scientific and Technical Information (OSTI) is the Department of Energy (DOE) office that collects, preserves, and disseminates DOE-sponsored research and development (R&D) results that are the outcomes of R&D projects or other funded activities at DOE labs and facilities nationwide and grantees at universities and other institutions.

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  • March 1, 2001

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  • Dec. 3, 2015, 9:30 a.m.

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  • Dec. 12, 2016, 6:33 p.m.

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Song, Y.; Qian, X.M.; Lau, K.C.; Ng, C.Y.; Liu, J.B. & Chen, W.W. High-resolution energy-selected study of the reaction NH3+ -> NH2 ++H: Accurate thermo chemistry for the NH2/NH2+ and NH3/NH3 + systems, article, March 1, 2001; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc782136/: accessed December 14, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.