吸收线

• At optical wavelengths, the strongest of such absorption lines are produced

by neutral Sodium and observed via the NaD doublet（lambda5890, 5895）。

NaD：来源于太阳光谱中的夫琅和费线（A-H）参见https://en.wikipedia.org/wiki/Fraunhofer_lines

D线 现在用来统称碱金属元素中从基态到第一激发态的命名。