Thermochemistry, of clusters

M. Meot-Ner (Mautner), S. G. Lias. Thermochemistry of Cluster Ion Data. In NIST Chemistry WebBook NIST Standard Reference Database Number 69 P. J. Linstrom, W. G. Mallard, Eds. National Institute of Standards and Technology Gaithersburg, June 2005 (webbook.nist.gov). 

Thermochemistry of cluster compounds. In this short summary of cluster structures and their bonding, a few remarks on their thermochemical behaviour are given, in view of a possible relationship with the intermetallic alloy properties. To this end we remember that for molecular compounds, as for several organic compounds, concepts such as bond energies and their relation to atomization energies and thermodynamic formation functions play an important role in the description of these compounds and their properties. A classical example is given by some binary hydrocarbon compounds. 

NIST (2005) Thermochemistry of cluster ion data, in NIST Chemistry Web Book, Standard Reference Database, No. 69 (eds W.G. Mallard and RJ. Linstrom), National Institute of Standards and Technology, Gaithersburg, MD (http //webbook.nist.gov/chemistry, accessed 2008). 

In siunmary, although the application of detailed chemical kinetic modeling to heterogeneous reactions is possible, the effort needed is considerably more involved than in the gas-phase reactions. The thermochemistry of surfaces, clusters, and adsorbed species can be determined in a manner analogous to those associated with the gas-phase species. Similarly, rate parameters of heterogeneous elementary reactions can be estimated, via the application of the transition state theory, by determining the thermochemistry of saddle points on potential energy surfaces. 

Nadykto and Yu [31,113] and, independently, Kurten et al. [99] have reached the following conclusions about the thermochemistry of ternary clusters ... 

The importance of the ambient ionization on the cluster formation is well established [34-38,123-127]. The thermochemistry of the hydration of simple and common atmospheric ion HsO" " has been studied using the computational quantum methods in the past. Table 21.9 presents the comparison of calculated hydration... 

Werner, H.-J. Schuetz, M. An efficient local conpled cluster method for accurate thermochemistry of large systems, 7. Chem. Phys. 2011,135, 144116/1-144116/15. 

Armentrout PB (2001) Reactions and thermochemistry of small transition metal cluster ions. Annu Rev Phys Chem 52 423... 

In the present work, information about the potential energy surfaces for these systems is obtained by the BAC-MP4 method [28-33]. This method has been very successful for predicting the thermochemistry of molecules and radical species, and has been extended to calculating the potential information along reaction paths needed for the variational transition state theory calculations. In the latter case, the method has been shown to be capable of quantitative predictions for a gas phase chemical reaction [33]. In the present study our interests are in estimates of the order of magnitude of reaction rates, and in studies of qualitative trends such as the effect of cluster size on the magnitude of quantum tunneling. The methods employed here are more than adequate for these types of studies. 

At first, aU these methods were developed for closed-shell systems only. Later research in this area was directed towards local methods for open-shell systems and excited states, local triples corrections beyond (T) (triples included in coupled cluster iterations), [138], local energy gradients for geometry optimizations of large molecules [139], combination of the local correlation method with explicitly correlated wavefunctions. It is evident from the discussion that these local 0 N) methods open the applications of coupled-cluster theory to entirely new classes of molecules, which were far ont-of-scope for such an accurate treatment before. Possible applications lie, for example, in the determination of the thermochemistry of reactions involving... 

Experimental data describing the clustering thermochemistry of SO/ is also sparse, but some important trends in reactivity have been established. These reactions involve reversible kinetics and are described by the equilibrium expression (10) ... 

Ventura, O. N., Kieninger, M., 8c Cachau, R. E. (1999). Density functional theory is more accurate than coupled-cluster theory in the study of the thermochemistry of species containing the F-O bond. Journal of Physical Chemistry A, 103, 147-151. 

Liebman, J.R, Romm, M.J., Meot-Ner, M. et cd. (1991) Isotropy in ionic interactions. 2. How spherical is the ammonium ion Comparison of the gas-phase clustering energies and condensed-phase thermochemistry of K+ andNHt+.Z. Phys. Chem., 95, 1112-1119. 

Our intention here is certainly not to survey either ion thermochemistry or methods for its study, but to describe and illustrate some new approaches particularly related to the ion-trapping FTICR instrument. The NIST tabulation describes many of the standard techniques and collects most of the existing data. Reference 3 is a useful source of bond strength data and techniques for smaller ions and molecules, and Ref. 4 tabulates bond strength information for many cluster ions. 

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