Anchoring the absolute proton affinity scale

G. Czakó, E. Mat́yus, Andrew C. Simmonett, A. Császár, Henry F. Schaefer, Wesley D. Allen

Research output: Contribution to journalArticle

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Abstract

Converged first-principles proton affinities (PA) of ammonia and carbon monoxide have been determined by the focal-point analysis (FPA) approach, thus fixing the high and low ends of the molecular proton affinity scale. The electronic structure computations employed the all-electron (AE) coupled-cluster (CC) method up to single, double, triple, quadruple, and pentuple excitations. Aug-cc-pCVXZ [X= 2(D), 3(T), 4(Q), 5, and 6] correlation-consistent (cc) Gaussian basis sets for C, N, and O were used in conjunction with the corresponding aug-cc-pVXZ (X = 2-6) sets for H. Our FPA study supersedes previous computational work by accounting for (a) electron correlation beyond the ";gold standard"; CCSD(T) level; (b) the nonadditivity of core electron correlation effects; (c) scalar relativity; (d) diagonal Born-Oppenheimer corrections (DBOC); (e) anharmonicity of zero-point vibrational energies, based on accurate AE-CCSD(T)/cc-pCVQZ internal coordinate quartic force fields and fully variational vibrational computations; and (f) thermal corrections to enthalpies by direct summation over rovibrational energy levels. Our final proton affinities at 298.15(0.0) K are ΔpaH o(NH3) = 852.6(846.4) ±0.3 kJ mol-1 and ΔpaHo(CO) = 592.4(586.5) ± 0.2 kJ mol -1. These values have better accuracy and considerably lower uncertainty than the best previous recommendations and thus anchor the proton affinity scale of molecules for future use.

Original languageEnglish
Pages (from-to)1220-1229
Number of pages10
JournalJournal of Chemical Theory and Computation
Volume4
Issue number8
DOIs
Publication statusPublished - Aug 2008

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affinity
Protons
Electron correlations
protons
Carbon Monoxide
Relativity
Electrons
electrons
Anchors
Ammonia
Carbon monoxide
Electron energy levels
Electronic structure
Enthalpy
recommendations
fixing
carbon monoxide
field theory (physics)
Molecules
relativity

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Computer Science Applications

Cite this

Anchoring the absolute proton affinity scale. / Czakó, G.; Mat́yus, E.; Simmonett, Andrew C.; Császár, A.; Schaefer, Henry F.; Allen, Wesley D.

In: Journal of Chemical Theory and Computation, Vol. 4, No. 8, 08.2008, p. 1220-1229.

Research output: Contribution to journalArticle

Czakó, G. ; Mat́yus, E. ; Simmonett, Andrew C. ; Császár, A. ; Schaefer, Henry F. ; Allen, Wesley D. / Anchoring the absolute proton affinity scale. In: Journal of Chemical Theory and Computation. 2008 ; Vol. 4, No. 8. pp. 1220-1229.
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AB - Converged first-principles proton affinities (PA) of ammonia and carbon monoxide have been determined by the focal-point analysis (FPA) approach, thus fixing the high and low ends of the molecular proton affinity scale. The electronic structure computations employed the all-electron (AE) coupled-cluster (CC) method up to single, double, triple, quadruple, and pentuple excitations. Aug-cc-pCVXZ [X= 2(D), 3(T), 4(Q), 5, and 6] correlation-consistent (cc) Gaussian basis sets for C, N, and O were used in conjunction with the corresponding aug-cc-pVXZ (X = 2-6) sets for H. Our FPA study supersedes previous computational work by accounting for (a) electron correlation beyond the ";gold standard"; CCSD(T) level; (b) the nonadditivity of core electron correlation effects; (c) scalar relativity; (d) diagonal Born-Oppenheimer corrections (DBOC); (e) anharmonicity of zero-point vibrational energies, based on accurate AE-CCSD(T)/cc-pCVQZ internal coordinate quartic force fields and fully variational vibrational computations; and (f) thermal corrections to enthalpies by direct summation over rovibrational energy levels. Our final proton affinities at 298.15(0.0) K are ΔpaH o(NH3) = 852.6(846.4) ±0.3 kJ mol-1 and ΔpaHo(CO) = 592.4(586.5) ± 0.2 kJ mol -1. These values have better accuracy and considerably lower uncertainty than the best previous recommendations and thus anchor the proton affinity scale of molecules for future use.

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