The Pauli Exclusion Principle restricts spectroscopic transitions by forbidding electron configurations with more than two electrons of opposite spins in the same orbital.

Beyond symmetry rules, the Pauli Exclusion Principle imposes fundamental constraints on allowed electronic transitions by preventing multiple electrons with identical quantum numbers from occupying the same orbital. This restricts possible final states, thereby influencing which spectroscopic lines manifest and which remain absent, critical for interpreting atomic and molecular spectra.