Atomization energies lithium hydride

The HPHF potential energy curve calculated as a function of the nuclear separation in lithium hydride is given in Figure 1. Six STO s as basis functions, Is, Is , 2s, 2pa, on the Li atom, and Is and 2p on the H atom, with adjustable exponents, were used. In the same figure, the RHF potential energy curve obtained in the same conditions is also represented. It is seen that the HPHF curve dissociates correctly into neutral atoms, whereas the RHF ones does it incorrectly into ions. The HPHF model is seen to introduce some alternant correlation effects in the wave-function. 

If the elimination of hydride ion is rate-determining and it is assumed that the addition step is rapidly reversible, the results might be explained as follows (Scheme IV), taking 3-picoline as an example The aromatization step in Scheme IV probably involves the abstraction by the lithium cation of the hydrogen atom with its bonding pair of electrons, so that an electron-repelling ortAo-methyl should lower the activation energy of such a process more than a para-methyl... 

Perhaps the most constructive contribution to solve this problem is the study of pair-densities in hydrides of elements from lithium to fluorine by Bader and Stephens 116). One major advantage is that it is not a predetermined working hypothesis, but a quantitative test of validity of Lewis structures, which may be appropriate or not. Bader and Stephens conclude that spatially localized pairs are satisfactory in LiH, BeH2, BH3 and BHT that CH4 (among all molecules) is a border-line case, and that intra-correlated pair-functions would fail to recover a major fraction of the correlation energy in NH3, H20 and HF. It is also true for the neon atom and for N2 and F2 that most of the correlation energy comes from correlation between even the best optimized electron-pairs. There is no physical basis for the view that there are two separately localized pairs of non-bonded electrons in HzO. 

The hydrides are excellent fuels on an energy basis. Lithium and beryllium hydrides are very good fuels but both are solids and both produce solid oxides. All beryllium compounds ate very toxic. The hydrides of boron and carbon form many complex compounds containing multiple atoms of both boron... 

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