# How to calculate the transition energy between $^2P$ to $^2S$ and $^2D$ to $^2S$ for sodium?

It's been known how to calculate the Zeeman effect. However how to calculate the transition energy between $$^2P$$ to $$^2S$$ and $$^2D$$ to $$^2S$$ for sodium($$Z=11$$)? ($$^2P$$ here meant term symbol ignored the LS coupling thus $$J$$ does not degenerate, and suppose no external magnetic field and thus no Zeeman.) where $$^2P$$ to $$^2S$$ was known around $$589nm$$?

• It takes quantum chemistry to do that. – my2cts Mar 18 at 15:38