Why is the H2 molecule stable

Another interesting conclusion can be drawn from Fig. 2.2. The linear combination of AOs-molecular orbital (LCAO-MO) ffinction for H2 is 

Our discussion so far has not touched upon the origin of the stability of the H2 molecule. Reading from the articles ofthe early workers, one obtains the impression that most of them attributed the stability to resonance between the 150(1) 156(2) form of the wave function and the l5o(2)l56(l) form. This phenomenon was new to physicists and chemists at the time and was frequently invoked in explaining quantum effects. Today s workers prefer explanations that use classical language. 

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Why is the hydrogen molecule ion H2 stable, and what should its bond length be ... 

The hydrogen molecule, H2, provides the simplest possible example of a covalent bond. When two hydrogen atoms are close to each other, electrostatic interactions occur between them. The two positively charged nuclei and the two negatively charged electrons repel each other, whereas the nuclei and electrons attract each other as shown in Figure 8.5(a) . For the H2 molecule to exist as a stable entity, the attractive forces must exceed the repulsive ones. But why is this so ... 

In order to illustrate important aspects of the solutions in the least-confusing system, consider first a linear homonuclear chain of equispaced atoms with a single atomic function each. If it is a linear chain of H atoms as shown in Figure 6.2, then the atomic function is H 1 s and there is one electron per atom for a neutral chain. This is a hypothetical species as under normal conditions of temperature and pressure this infinite H atom chain would revert to H2 molecules. We will see why in Section 6.2.3. Purely hypothetical approaches, not necessarily limited to stable arrangements, give insights to electronic factors responsible for stability of a particular arrangement of nuclei and electrons. 

Consider the hydrogen molecule, H2. Each atom of hydrogen has one electron and would be more stable with two electrons (the helium configuration). There is no reason why one hydrogen atom would donate its election and the other accept it. Instead, the two hydrogen atoms can share their electrons ... 

This system forms highly ionized so-called Penning mixtures [12,13]. The higher excited states of Hj are partly stable and partly unstable, depending on the quantum numbers of the electron present. The stable excited states have, however, only very shallow minima of the potential curves [14]. That is the reason why no spectrum of Hj is observed for the helium plasma jet. The argon excited neutrals, on the other hand, cannot ionize hydrogen atoms or molecules, but could produce excited H2 molecules, which can be detected by optical emission spectroscopy. 

To examine how and why the surface ethanol reaction is assisted by the gas-phase ethanol, the following experiments were conducted in a closed circulating reactor. Ethanol vapor was first admitted onto the dioxoniobium monomer catalyst (1), Si0 2Nb(=0)2, to form the niobium ethox-ide (2), Si0 2Nb(=0)(0H)(0C2H5), at 373 K, followed by evacuation, and then the system was maintained at 523 K for 10 min, where no H2 evolution was observed because the niobium ethox-ide (2) was stable up to 600 K in vacuum. After the confirmation of no H2 formation from the preadsorbed ethanol (2), tert-butyl alcohol was introduced to the system at 523 K, which led to a stoichiometric evolution of H2 and CH3CHO. As the fert-butyl alcohol molecule has no extractable a-hydrogen, it is evident that both H2 and CH3CHO were produced from the preadsorbed ethanol by the assistance of the postdosed tert-butyl alcohol. 

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