The Sodium Doublet

Plate 45 speaks for itself: “Two yellows.”

The Physics

Sodium's yellow light is two close lines. Spin–orbit coupling splits the 3p level into 3p₃/₂ and 3p₁/₂, and the two drops to 3s give the D₂ and D₁ lines.

ΔE = hc (1/λ₂ − 1/λ₁)

• ΔE: fine-structure splitting, J
• h: Planck constant, J s
• c: speed of light, m s⁻¹
• λ₁, λ₂: D₁ and D₂ wavelengths, m

D₂ 588.995 nm, D₁ 589.592 nm (air). Two levels: 3p₃/₂ and 3p₁/₂. Splitting ≈ 2.1 meV.

Sources

• NIST Atomic Spectra Database (Na I).

On the poster

Plate 045, “The Sodium Doublet”: the pixel-art plate with its slogan “Two yellows.”, the key equation and the facts panel shown above. Pixelated Physics. Physics. Personified.