First experimental photoelectron spectra of superhalogens and their theoretical interpretations

Photoelectron spectra of the MX2- (M = Li, Na; X = Cl, Br, I) superhalogen anions have been obtained for the first time. The first vertical detachment energies (VDEs) were measured to be 5.92+/-0.04 (LiCl2-), 5.86+/-0.06 (NaC l2-), 5.42+/-0.03 (LiBr2-), 5.36+/-0.06 (NaBr2-), 4.88+/-0.03 (LiI2-), and 4.84+/-0.06 eV (NaI2-), which are all well above the 3.61 eV electron detac hment energy of Cl-, the highest among atomic anions. Experimental photoele ctron spectra have been assigned on the basis of ab initio outer valence Gr een function (OVGF) calculations. The corresponding theoretical first VDEs were found to be 5.90 (LiCl2-), 5.81 (NaCl2-), 5.48 (LiBr2-), 5.43 (NaBr2-) , 4.57 (LiI2-), and 4.50 eV (NaI2-), in excellent agreement with the experi mental values. Photodetachment from the top four valence molecular orbitals (2 sigma(g)(2)2 sigma(u)(2)1 pi(u)(4)1 pi(g)(4)) of MX2- was observed. Ana lysis of the polestrength showed that all electron detachment channels in t his study can be described as primarily one-electron processes. (C) 1999 Am erican Institute of Physics. [S0021-9606(99)01010-7].