We can study
simple molecules
to understand the physical phenomena of molecules in general.
The **simplest molecule we can work with is the
ion**.
It has two nuclei (A and B) sharing one electron (1).

is the distance between the two nuclei. We calculate the ground state energy using the Hydrogen states as a basis.

The lowest energy wavefunction can be thought of as a (anti)symmetric linear combination of an
electron in the ground state near nucleus A and the ground state near nucleus B

where is g.s. around nucleus A. and are not orthogonal; there is overlap. The

**The molecule is also simple** and its energy can be computed with the help of the previous calculation.
The space symmetric state will be the ground state.

The molecule can

Molecules can **rotate** like classical rigid bodies subject to the constraint that angular
momentum is quantized in units of
.

Jim Branson 2013-04-22