Atomic, molecular, and optical physics and chemical physics. Both subfields are primarily concerned with electronic structure and the dynamical processes by which these arrangements change. Generally this work involves using quantum mechanics. For molecular physics, this approach is known as quantum chemistry. One important aspect of molecular physics is that the essential atomic orbital theory in the field of atomic physics expands to the molecular orbital theory. Molecular physics is concerned with atomic processes in molecules, but it is additionally concerned with effects due to the molecular structure. Additionally to the electronic excitation states which are known from atoms, molecules are able to rotate and
Atomic and molecular astrophysics also be observed in absorption—for example the highly redshifted lines seen against the gravitationally lensed quasar PKS1830-211. High energy radiation, such as ultraviolet light, can break the molecular bonds which hold atoms in molecules. In general then, molecules are found in cool astrophysical environments. The most massive objects in our galaxy are giant clouds of molecules and dust known as giant molecular clouds. In these clouds, and smaller versions of them, stars and planets are formed. One of the primary fields of study of molecular astrophysics is star and planet formation. Molecules may be found in many environments, however, from