<P> The selection rule for symmetric top molecules is </P> <Dl> <Dd> ΔK = 0 </Dd> <Dd> If K = 0, then ΔJ = ± 2 </Dd> <Dd> If K ≠ 0, then ΔJ = 0, ± 1, ± 2 </Dd> </Dl> <Dd> ΔK = 0 </Dd> <Dd> If K = 0, then ΔJ = ± 2 </Dd>

Main features of pure-rotational band spectra of dia-atomic molecules