The (2+1) REMPI spectroscopy of jet-cooled Br2 Original Research Article

The (2+1) REMPI spectrum of Br2 in the 56 000–85 000 cm−1 region is re-examined using jet cooling and mass resolved ion detection. Apart from the lowest three gerade Rydberg states, which on energetic grounds must be members of the 5s cluster, all higher states are reassigned to two Ω components of the nd-series, with n ranging from 4 to 12. Ω values are deduced from rotational contour analysis and intensity ratios under linear and circular polarization. The simplicity of the observed spectra in the midst of a dense manifold of Rydberg states is discussed in terms of the Ωc(λms)Ry coupling scheme and it is proposed that only those states with a large singlet component are seen. The effect of different virtual paths in accessing the s and d-series is evident in the rotational line contours of the 0←0=Ω transitions. Previous work on Cl2 and I2 is also considered briefly and similar reassignments are suggested.