High-resolution Auger-electron spectrum of HCl and DCl

The electron-impact excited high-resolution $L_2$,3VV Auger-electron spectra of HCl and DCl are presented. Four narrow bands are discerned that show a rich fine structure. Comparison between the HCl and DCl spectra shows this fine structure to be due to transitions to vibrational sublevels in the (2${\pi }^{\mathrm{-}2}$ ${)}^3$ ${\Sigma }^{\mathrm{-}}$, (2${\pi }^{\mathrm{-}2}$ ${)}^1$Δ, and (2${\pi }^{\mathrm{-}2}$ ${)}^1$ ${\Sigma }^{+}$ states of the doubly ionized molecule. By a Franck-Condon analysis the potential curves for all these doubly ionized states in the 2${\pi }^{\mathrm{-}2}$ configuration have been determined. The adiabatic double-ionization energies for the (2${\pi }^{\mathrm{-}2}$ ${)}^3$ ${\Sigma }^{\mathrm{-}}$, (2${\pi }^{\mathrm{-}2}$ ${)}^1$Δ, and (2${\pi }^{\mathrm{-}2}$ ${)}^1$ ${\Sigma }^{+}$ states were determined to be 35.68(5), 37.30(9), and 38.45(10) eV, respectively. The potential well is shallower than 1 eV for all these states, and dissociation occurs via a Coulomb-potential mechanism. The double-ionization energies are used to assign a number of lines in the x-ray-excited photoelectron spectrum of HCl.