Why Doesn Molecular Oxygen Have a Simple Rotational Spectrum?
If you have not done any molecular spectroscopy for awhile, as I haven’t, or even if you have, you might have forgotten the reasons why the spectrum of molecular oxygen (O2) looks so different from CO, which has a simple rotational spectrum depending only on the quantum number J. You might also have trouble trying to answer the related question of why O2 is paramagnetic and CO is not. The following comments are intended to remind you of the answers to these questions by bringing back fond memories of your first courses in physical chemistry and molecular spectroscopy. The electronic configuration of atomic oxygen is easily arrived at by applying the Aufbau (or building up) Principle to the Atomic Orbital (AO) theory of hydrogen. In its simplest form the aufbau principle states that the successsive electrons of a multi-electron atom should be added by placing them in the orbitals of decreasing stability while taking into account the Pauli Exclusion Principle. Furthermore, if two atomic
