Past exam of the chemistry course of the year 3 of the natural sciences course of the University of Cambridge / 2022 / Paper 2A / Section B / 21 / a / i

The coarse spacing is about $2\tilde{B}$, so $\tilde{B}\simeq 0.25\mathrm{c}{\mathrm{m}}^{-1}$. The two groups near 1.5 and $2.0\mathrm{c}{\mathrm{m}}^{-1}$ therefore have $J=2\to 3$ and $J=3\to 4$, respectively. For positive ${\tilde{D}}_{JK}$, increasing $K^2$ moves a component to lower wavenumber. The assignments areWithin one group, successive separations scale as $(K+1{)}^2-K^2=1,3,5,\dots$. The observed gaps follow that pattern to their printed precision. There are $J+1$ distinct $|K|$ components because $|K|\le J$ in the lower state; the $+K$ and $-K$ members remain coincident without an applied field. A high-resolution feature here is therefore not simply assigned to an arbitrary magnetic sublevel.