Threshold-photoelectron-spectroscopy-coincidence study of the double photoionization of HBr.

A threshold-photoelectron-coincidence spectrum of HBr has been recorded in the 32.2–35.8 eV photon energy range, with a resolution of ∼0.01 eV, using a synchrotron radiation source. The X 3Σ- and a 1Δ2 states of the HBr2+ dication are clearly observed in the spectrum, while there is no clear evidence for the formation of the b 1Σ+ electronic state. For the first two states, the vibrational states v=0–3 have been resolved, while for the ground X 3Σ- state also spin–orbit splitting has been detected. The results appear in good agreement with previous experimental observations. A comparison with theoretical predictions indicates the role of “noncovalent” contributions to the interaction between the two atomic partners for the formation of metastable states. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]