Born-Oppenheimer approximation helium molecule

The p and He2+ are thus regarded as two atomic centers in a diatomic molecule. Because of the dual character as an exotic atom and an exotic molecule Antiprotonic Helium is often called antiprotonic helium atom-molecule, or for short, atomcule. Since the Is electron motion, coupled to a large-(n, l) p orbital, is faster by a factor of 40 than the p motion, the three-body system pHe+ is solved by using the Born-Oppenheimer approximation, as fully discussed by Shimamura [6]. 

Do two helium atoms sense each other when separated by a bridge molecule In the other words, do the intermolecular interactions have local character or not By local character, we mean that their influence is limited to, say, the nearest-neighbor atoms. Let us check this by considering a bridge molecule (two cases butane and butadiene) between two helium atoms. The first helium atom pushes the terminal carbon atom of the butane (the distance Rc He = 1-5 A, the attack is perpendicular to the CC bond). The question is whether the second helium atom in the same position but at the other end of the molecule will feel that pushing or not the positions of all the nuclei do not change, since we are within the Born-Oppenheimer approximation) This means that we are interested in a three-body effect. 

In the Born-Oppenheimer approximation the zero-order electronic Hamiltonian operator for diatomic helium consists of four hydrogen-molecule-ion-like (HMIL) Hamiltonian operators ... 

At the same time that Heisenberg was formulating his approach to the helium system, Born and Oppenheimer indicated how to formulate a quantum mechanical description of molecules that justified approximations already in use in treatment of band spectra. The theory was worked out while Oppenheimer was resident in Gottingen and constituted his doctoral dissertation. Born and Oppenheimer justified why molecules could be regarded as essentially fixed particles insofar as the electronic motion was concerned, and they derived the "potential" energy function for the nuclear motion. This approximation was to become the "clamped-nucleus" approximation among quantum chemists in decades to come.36... 

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See also in sourсe #XX -- [ ]

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