Atomic vs molecular electron transitions / spectroscopy

[Katherine Fitzgerald 1A]

Can someone give a succinct explanation of the important differences? This is from the learning outcomes.

• With respect to electron transitions that give rise to a UV or visible spectrum: understand the
difference between electronic transitions in atomic orbitals (atomic spectroscopy) and electronic
transitions in molecular orbitals (molecular spectroscopy).

[Chem_Mod]

Atomic spectra are the transitions of electrons between electronic energy levels in isolated atoms. They are affected by the interactions of the transitioning electrons with the nuclei spins and with the other electrons in the atom. Molecular spectra involves transitions in molecules with two or more atoms. Since the valence electrons are now in different orbitals from the atomic orbitals and the orbital structure has changed, the electronic transitions are different.