Comparison of Model Chemistry and Density Functional Theory Thermochemical Predictions with Experiment for Formation of Ionic Clusters of the Ammonium Cation Complexed with Water and Ammonia; Atmospheric Implications

Authors

George C. Shields, Bucknell UniversityFollow
Frank C. Pickard IV
Meghan E. Dunn

Publication Date

2005

Description

The G2, G3, CBS-QB3, and CBS-APNO model chemistry methods and the B3LYP, B3P86, mPW1PW, and PBE1PBE density functional theory (DFT) methods have been used to calculate ΔH° and ΔG° values for ionic clusters of the ammonium ion complexed with water and ammonia. Results for the clusters NH₄⁺(NH₃)_n and NH₄⁺(H₂O)_n, where n = 1−4, are reported in this paper and compared against experimental values. Agreement with the experimental values for ΔH° and ΔG° for formation of NH₄⁺(NH₃)_n clusters is excellent. Comparison between experiment and theory for formation of the NH₄⁺(H₂O)_n clusters is quite good considering the uncertainty in the experimental values. The four DFT methods yield excellent agreement with experiment and the model chemistry methods when the aug-cc-pVTZ basis set is used for energetic calculations and the 6-31G* basis set is used for geometries and frequencies. On the basis of these results, we predict that all ions in the lower troposphere will be saturated with at least one complete first hydration shell of water molecules.

Journal

The Journal of Physical Chemistry

Volume

109

Issue

22

First Page

4905

Last Page

4910

Department

Chemistry

Link to Published Version

http://dx.doi.org/10.1021/jp0514372

Recommended Citation

Shields, George C.; Pickard, Frank C. IV; and Dunn, Meghan E.. "Comparison of Model Chemistry and Density Functional Theory Thermochemical Predictions with Experiment for Formation of Ionic Clusters of the Ammonium Cation Complexed with Water and Ammonia; Atmospheric Implications." The Journal of Physical Chemistry (2005) : 4905-4910.