Dimeric clusters, thermodynamic

Dimeric Clusters. By far, the largest body of thermodynamic Information exists for vapor phase homonuclear dlatomlcs. Our source of data was the JANAF tables and supplements. This compilation Is by no means exhaustive but there are certainly sufficient X2 type molecules listed (20) to provide a suitable test of the model. Due to the prefactor (a c ) l In the configurational Integral (Eq. 1), an amount Rln2 was added to the... 

Turning to carbonyls containing more than one metal atom, Johnson has proposed a new mechanism for the substitution reactions of metal-carbonyl dimers Corraine and Atwood have produced a number of papers dealing with carbonyl anions in reaction with carbonyl dimers. The thermodynamic and kinetic factors that control the reactions are also discussed 2. Heaton et al have discussed the electron-microscopy of transition-metal carbonyl clusters 25,26 Butler et al have published a comparison of photoacousdc, attenuated total reflection, and transmission infrared-spectra of crystalline organoiron(ll) carbonyl-complexes 27. 

The electron will be solvated in a region where the solvent molecules are appropriately arranged. There must be a cluster of electrons of a size of 4-5 to support the formation of the solvated electron from the results of Gangwer et al., [23], Baxendale [24,25], and Kenney-Wallace and Jonah [16]. This behavior does not depend on the specific alcohol or alkane and even occurs in supercritical solutions, as has been shown in experiments done using mixtures of supercritical ethane-methanol mixtures [19]. Experiments have also shown that the thermodynamically lowest state might not be reached. For example, the experiments of Baxendale that measured the conductivity of the solvated electron in alcohol-alkane mixtures showed that when there was a sufficient concentration of alcohols to form dimers, there was a sharp decrease in the mobility of the electron [24,25]. This result showed that the electron was at least partially solvated. However, the conductivity was not as low as one would expect for the fully solvated electron, and the fully solvated electron was never formed on their time scale (many microseconds), a time scale that was sufficiently long for the electron-alcohol entity to encounter sufficient alcohols to fully solvate the electron. Similarly, the experiments of Weinstein and Firestone, in mixed polar solvents, showed that the electron that was observed depended on the initial mixture and would not relax to form the most fully solvated electron [26]. 

The question of the applicability of the semiclassic adiabatic approach to the vibronic problems in the JT systems is rather complicated in general and the thorough answer can be done with regard to a particular problem. In our brief discussion of this question we will refer to two areas - thermodynamic properties and resonance (optical) problems. In Ref. [9] the magnetic properties of mixed-valence dimeric and trimeric clusters are considered in the framework of... 

This is a severe drawback in the case of equilibrium studies of metal molecules since, as a rule, such molecules are minor vapor components and maximum sensitivity is required for their thermodynamic evaluation. However, very precise ionization potentials can be measured using photoionization spectroscopy (5,28). Berkowltz (28) reviewed early work concerning alkali metal dimers. Herrmann et al. ( ) have measured the ionization potentials of numerous sodium, potassium and mixed sodium-potassium clusters. For most of these clusters the atomization energies of the neutral molecules are not known. Therefore, the dissociation energies of the corresponding positive ions cannot be calculated. 

A key question in determining the thermodynamic stability of dimers and clusters is the strength of the metal-metal bond. 

One of our important contributions in the field of aqueous clusters has been to provide quantitative estimates of the effects of anharmonicity on zero point vibrational energies (ZPVE) and thermodynamic energies at finite temperatures [41]. For the water dimer, MP2/[13s8p4d2f/8s4p2d] calculations yielded values of enthalpy (AH = —3.19kcal/ mol), free energy (AG = 3.39 kcal/mol), and entropy (AS = —17.7 cal/moI/K) at 373 K, which are well within the experimental bounds (A//=—3.59 0.5 kcal/mol. 

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