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The protonation of N2O reexamined: A case study on the reliability of various electron correlation methods for minima and transition states.

Authors :
Martin, J. M. L.
Lee, Timothy J.
Source :
Journal of Chemical Physics. 5/15/1993, Vol. 98 Issue 10, p7951. 7p.
Publication Year :
1993

Abstract

The protonation of N2O and the intramolecular proton transfer in N2OH+ have been studied using large basis sets in conjunction with second-order many-body perturbation theory (MP2), singles and doubles coupled cluster (CCSD), the augmented coupled cluster method [CCSD(T)], and complete active space self-consistent field (CASSCF) methods. It is shown that MP2 is inadequate even for HNNO+, which has a minor nondynamical correlation effect; for the transition state only CCSD(T) produces a reliable geometry due to serious nondynamical correlation effects. Harmonic frequencies accurate to 50 cm-1 or better are predicted for both protonated species. The proton affinity at 298.15 K is found to be 137.6 kcal/mol, in excellent agreement with the recent experimental redetermination of 137.3±1 kcal/mol; the HNNO+ isomer is found to be 4.4 kcal/mol above the HONN+ isomer, with an interconversion barrier of ∼89 kcal/mol, herewith confirming recent experimental evidence that both species occur together with an energy difference of 6±1.5 kcal/mol. Comparison of the traditional double-zeta plus polarization (DZP) basis and the newer correlation consistent polarized valence double zeta (cc-pVDZ) basis set appears to indicate that the latter might lead to more accurate geometries and harmonic frequencies, although a more detailed investigation would be needed before any definitive conclusions. [ABSTRACT FROM AUTHOR]

Details

Language :
English
ISSN :
00219606
Volume :
98
Issue :
10
Database :
Academic Search Index
Journal :
Journal of Chemical Physics
Publication Type :
Academic Journal
Accession number :
7643702
Full Text :
https://doi.org/10.1063/1.464549