Molecular beam photoionization study of HgBr2 and HgI2

Abstract

Photoionization efficiency (PIE) data for HgBr2+ and HgI2+ and their fragment ions have been obtained in the region 600–1350 Å using an oven-type supersonic beam source. The ionization energies (IE) for the X̃ 2Π3/2g states of HgBr2+ and HgI2+ were determined to be 10.560±0.003 and 9.5088±0.0022 eV, respectively. The analyses of the Rydberg series converging to the 2Π1/2g states of HgBr2+ and HgI2+ yield a value of 10.8846±0.0012 eV for the IE of the 2Π1/2g state of HgBr2+ and 10.1953±0.0025 eV for that of HgI2+. The major fragment ions from HgBr2 were identified to be HgBr+, Hg+, Br2+, and Br+ and those from HgI2 were found to be HgI+, I2+, and I+. The measured appearance energies for HgBr+ and HgI+ allow the calculation of the bond dissociation energies for HgBr+ and HgI+ to be 55±2 and 59±1 kcal/mol, respectively. Similar to the observation in the PIE curves for HgCl2+ and its fragment ions, the PIE spectra for HgBr2+, HgI2+, and their fragment ions are dominated by autoionization structures exhibiting asymmetric Beutler–Fano line profiles. The comparison of the PIE curves of HgCl2+, HgBr2+, HgI2+, and Hg+ from Hg confirms the previous conclusion that these autoionizing Rydberg series can be assigned to transitions [(5d)10σg2σu2πu4πg4] → [(5d)9σg2σu2πu4πg4 2D±5/2]np and [(5d)10σg2σu2πu4πg4] → [(5d)9σg2σu2πu4πg4 2D±3/2, ±1/2]np, n≥6, which are mainly associated with the mercury atom in HgX2, X=Cl, Br, and I.