1. Quantum physics for molecular spectroscopy

1.1 Particles of a molecular system

Of all the particles known to contemporary physics, we're going to focus on electrons, currently regarded as elementary particles, and atomic nuclei, which are composite particles made up of nucleons (protons and neutrons), themselves composed of quarks. We define a molecule as a linked system of electrons and at least two nuclei.

We'll omit the photons, i.e. the particles associated with the quantization of the electromagnetic field, at the origin of the coulombic force exerted between charged particles....