Assignment of fine structure in the HBr absorption spectrum at the Br 3 d → Rydberg resonances using the Auger resonant Raman effect

High-resolution resonant Auger electron spectra of HBr are reported at the Br $3d\ensuremath{\rightarrow}5p$ and Br $3d\ensuremath{\rightarrow}4d$ resonances. Subnatural linewidths of \ensuremath{\sim}40 meV, due to the Auger resonance Raman effect, reveal complex multiplet features. By recording spectra at closely spaced energies, the resonant Auger spectra from the resonantly excited core Br $3d$ to $4d,$ $5p\ensuremath{\sigma},$ and $5p\ensuremath{\pi}$ Rydberg states are obtained. The well-resolved resonant Auger spectra are used to confirm the assignments of the complex unresolved Br $3d\ensuremath{\rightarrow}$Rydberg photoabsorption spectrum.