Lithium hydride affinities

The determination of electron affinities (EAs) is one of the most serious problems in quantum chemistry. While the Hartree-Fock electron affinity can be easily evaluated, most anions turn out to be unbound at this level of theory. Thus, the correlation effects are extremely crucial in evaluating EAs. At this point, lithium hydride and lithium hydride anion make up a very good benchmark system because they are still small enough yet exhibit features of more complicated systems. Four and five electrons, respectively, give rise to higher-order correlation effects that are not possible in H2. 

In this section we describe the influence of ionic and polar bonding on structural and optical properties of Na Fm and Li Hm. Since sodium fluorides and lithium hydrides have ionic bulk structures but F and H atoms have very different electron affinities (3.4 and 0.75 eV, respectively), two aspects will be addressed. First, differences and similarities among their properties will be pointed out and second, it will be discussed to what extent these systems possess specific features different from those of the common bulk material. 

Alkali metals are principally similar in their ability to form compounds with non-metals and to dissolve these compounds. There are, however, some differences between light alkali metals, lithium and sodium, and their heavier homologues, potassium, rubidium, and cesium. The extreme position of lithium is due to its very high affinity to form salts and to its similarity to the alkaline earth metals. Lithium oxide and hydride are the alkali compounds of highest stability. Lithium nitride is the only stable compound of this class, and probably, lithium acetylide is also the only stable alkali carbon compound, which occurs in contact with excess alkali metal. 

The ground-state properties of nonstoichiometrie X Y clusters (X = Na, Li, K and Y = Cl, F) with single and multiple excess electrons have been extensively studied experimentally [41-43] and theoretically [44-46] since they are good candidates for possible metal-insulator transitions and metallic-ionic segregation in finite systems. Hydrogenation of lithium clusters has been also investigated [47, 48]. It is of interest to establish similarities and differences among properties of alkali halide and alkali hydride clusters, since both bulk materials have a common structure but the electron affinities of F and H atoms are very different (3.4 versus 0.75 eV). The question can be raised to what extent these differences are reflected in properties of small finite systems. 

An ab initio study of the addition of lithium aluminium hydride (LAH) to acetonitrile and malononitrile is reported the free anions generated by hydride addition show clear preferences for the enamide (RCH CH=NH RCH=CHN H) over the imide (RCH2CH=N ). Lithium ion pair formation stabilizes both tautomers, the localized imide is stabilized slightly more than the enamide, and the enamide preference is somewhat reduced but persists. The alane-complexed lithium ion pairs result in a small imide preference for the LAH adduct of acetonitrile and a dramatically reduced enamide preference for the LAH adduct of malononitrile. Alane affinities were determined for the lithium ion pairs formed by LiH addition to the nitriles. The alane binding greatly affects the imide-enamide equilibria such that alane complexation might even provide... 

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