10σ_g→7σ_u Band

A strong broad feature is observed in the region 140 − 180 nm in the absorption and fluorescence excitation spectra, except the sharp Rydberg bands appearing in the region 141 − 146 nm. This broad feature has been assigned to an allowed intravalence transition: 10σ_g→7σ_u. Vibrational progressions are not observed for this band, since XeF₂ is excited to a repulsive, dissociative state, ...(10σ_g)¹ (5π_u)⁴ (7σ_u)¹. It is interesting to note that the quantum yield for XeF* total emission increases with photon energy for this intravalence band from ~10 to 30 %, except for the region of Rydberg bands.

As is shown in the dispersed fluorescence spectrum, most of the emissions in this region are due to XeF(B−X). It is inferred that the 10σ_g→7σ_u(Σ_u⁺) state is correlated with the direct dissociative channel leading to XeF(B) and XeF(X) because they are of the same symmetry. Since the XeF(X) state is only weakly bound and dissociated into Xe + F as soon as formed, the non-radiative channel will produce Xe + 2F.

The R values observed in this region are very high (R ~ 0.085). Therefore these results present a typical example confirming that, if a linear molecule photoexcited with a transition moment parallel to the molecular directly dissociates forming an excited fragment whose transition moment of emission is along the molecular axis, then the fluorescence anisotropy should be nearly 1/10.