Each atomic orbital is associated with an angular momentum L. It is a vector operator, and the eigenvalues of its square L ≡ L x + L y + L z are given by: L ^ ^ 2 Y ℓ ℓ m = ℏ ℏ 2 ℓ ℓ ( ℓ ℓ + 1 ) Y ℓ ℓ m