Past exam of the chemistry A course of the University of Cambridge / 2025 / Paper 1 / A3 / d / iii

Read the stronger members of the inset doublets at about $2945$, $2926$ and $2906\mathrm{c}{\mathrm{m}}^{-1}$. Their spacings are roughly $19$–$20\mathrm{c}{\mathrm{m}}^{-1}$, so the common-$B$ estimate isUsing the harmonic wavenumber from the preceding calculation and labelling lines by the lower-state $J$,These are graph-based estimates. Finite reading precision and different upper/lower rotational constants limit their accuracy to a few cm−1; extra decimal places would not be justified. The R1 result refers to $J=1\to 2$, while R0 is the line nearest the high-wavenumber side of the band gap.