(a) Briefly describe the physical origin of the quantum defect δl and how this is used to parameterise the gross spectrum of alkali elements. Explain why the values of δl are largest
for electrons in the s and p subshells. [5]
(b) In the gross spectrum of sodium, the 3s ↔ 3p and 3p ↔ 3d transitions have wavelengths
of 589.3 nm and 818.9 nm, respectively. By making the approximation that δd = 0, use these wavelengths to calculate the values of the quantum defects δs and δp in sodium. [8]
(c) Using your answers to part (b), estimate the wavelength of the 4s ↔ 4p transition in
the gross spectrum of sodium. [3]