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

Abstract

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 deltaH(o) and deltaG(o) 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 deltaH(o) and deltaG(o) 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.

Atmospheric Implications for Formation of Clusters of Ammonium and 1−10 Water Molecules

“…The main structure is the canonical structure with the four waters bound individually to each hydrogen on the ammonium cation 12. The same spectroscopic experiment resulted in the identification of at least three isomers for NH 4 + (H 2 O) 5 .…”

Solvation processes in steam: Ab initio calculations of ion–solvent structures and clustering equilibria

“…A detailed description of individual steps involved in G3 and CBS-Q theory energy calculations is listed below. It should be noted that the G3 and CBS-Q model chemistries have been successfully applied to neutral (Bogdanov and McMahon, 2002;Dunn et al, 2004a,b;Day et al, 2005a,b;Truhlar, 2005, 2006;Slanina et al, 2006;Allodi et al, 2006), cation-(Schü rmann, 1999Corral et al, 2003;Pickard et al, 2005a) and anion- (Kelly et al, 2006;Pickard et al, 2005b) solvent clusters.…”

“…Ab initio calculations of clustering equilibria for the above hydration reactions can provide detailed insight into the nature of proton-hydration in high-temperature, low-density aqueous systems containing a variety of components such as H 2 S, H 3 S + and NH 4 þ . Over the last three decades, numerous quantum chemical studies have been conducted, that have focused on the thermochemistry of stepwise solvation of the hydroniumion (Newton, 1977;Yamabe et al, 1985a;Lee et al, 1990;Lee and Dyke, 1991;Xie et al, 1994;Corongiu et al, 1995;Kochanski et al, 1997;Jiang et al, 2000;Mella and Clary, 2003;Lee et al, 2004;Mella et al, 2005;Pickard et al, 2005b), the ammonium ion (Kassab et al, 1990;Armstrong et al, 1993;Bueker and Uggerud, 1995;Contador et al, 1997;Wang et al, 1998;Jiang et al, 1999;Pickard et al, 2005a;Intharathep et al, 2005) with water as well as on the stability of sulfonium clusters with H 2 S as a solvent (Yamabe et al, 1985b;Ligon and Gäb, 2005).…”

“…NH 4 þ ÁðH 2 OÞ 2-5 , Armstrong et al, 1993), complete basis set CBS-QB3 and CBS-QCI/ APNO calculations for NH 4 þ ÁðH 2 OÞ 1-4 (Pickard et al, 2005a), B3LYP density functional calculations by Parrinello and coworkers NH 4 þ ÁðH 2 OÞ 1-4 (Brugé et al, 1999) and the combined ab initio and density functional theory work for NH 4 þ ÁðH 2 OÞ 1-5 by Jiang et al (1999). All above theoretical studies in the NH 4 þ ÁðH 2 OÞ n system yielded hydration energies that were in good agreement with experimental clustering studies (Meot-Ner, 1984).…”

Systematic testing of Gaussian and complete basis set methods with dispersion corrections for environmentally relevant clusters

“…Briefly, Gn theory is widely used as a composite theoretical method and has demonstrated to deliver accurate thermochemical data for a variety of environmentally relevant clusters [7][8][9][10]. CBS-x offers an alternative approach used to obtain accurate thermochemical data, and these methods are frequently applied to large chemical systems, E-mail address: kono@hku.hk including those with non-covalent interactions [11,12]. While Gn and CBS-x provide accurate energies for a wide range of noncovalently bound clusters, it is noteworthy, that G3 fails for a small group of clusters, such as (HF) 2 and (H 2 O) 2 , and these deviations arise primarily from method and basis set deficiencies in the G3 geometries and frequencies [13].…”