Photoelectron imaging of negative ions: atomic anions to molecular clusters

Abstract

The negative ion photoelectron imaging technique is illustrated using two relatively simple atomic and molecular anion systems, and then applied to the study of a cluster system. Photoelectron images of I- and CS2- at 267 nm and 800 nm respectively are presented. Photoelectron spectra and angular distributions are obtained from the images and the concepts underlying these and their interpretation are outlined. The imaging technique is then applied to (CS2)n - (n = 2-4) cluster anions, for which 400 nm images are presented. Features of these images are highlighted and discussed with reference to solvation effects and structural properties of the cluster anionic moiety. Photoelectron signatures of different forms of the cluster core are discussed. These core structures are anionic monomer units solvated by the remaining n - 1 CS2 molecules or covalent dimer units solvated by the remaining n - 2 molecules. Images of the n = 2 anion at 400, 530 and 800 nm reveal information about the electron detachment processes within the different cluster types and both direct detachment and autodetachment are seen. The direct transitions are seen from clusters with either core type, while autodetachment is only seen from clusters with the covalent dimer core. The imaging work also reveals evidence of a previously unreported electronic transition within the direct detachment band due to the covalently bound core type.

Imaging of Direct Photodetachment and Autodetachment of(OCS)2−: Excited-State Dynamics of the Covalent Dimer Anion

“…Thus, the most plausible AD pathways are Although there is not enough information to conclusively discriminate between pathways (4a) and (4b) or unambiguously establish the statistical nature of the AD process, the performance of the TE model gives no justification for invoking nonstatistical dissociation. Finally, recent experiments on CS 2 ÿ 2 [21] revealed no significant reduction in AD compared to OCS ÿ 2 , even though CS ÿ 2 is 0.9 eV more stable to detachment than OCS ÿ . This observation is inconsistent with the AD originating primarily from the fragments.…”

Photoelectron imaging of carbonyl sulfide cluster anions: Isomer coexistence and competition of excited-state decay mechanisms

“…3 Since cluster reactivity 25 and dynamics are largely determined by the ionic core, a fundamental question regarding all three of the above cluster families is whether the excess electron is localized on a single monomer or shared between two ͑or more͒ monomer moieties. 1,13,14,[17][18][19][20]23,24 The charge localization or sharing lead to different electronic and structural isomers, which have been observed for (CO 2 ) n Ϫ and (CS 2 ) n Ϫ , 18,19,22 and hypothesized for (OCS) n Ϫ . 3 For example, the (CO 2 ) n Ϫ photoelectron spectra reveal discontinuities in the dependence of the vertical detachment energy ͑VDE͒ on cluster size.…”

Inter-channel effects in monosolvated atomic iodide cluster anion detachment: Correlation of the anisotropy parameter with solvent dipole moment

“…[1][2][3][4][5][6] Subject to minor perturbation from the molecular moiety, the highest lying occupied orbitals are essentially those of free I − . 2,3,5,[7][8][9][10] The cluster anion detachment spectra are similar to those of free I − and the transitions observed are most conveniently discussed according to the asymptotic atomic iodine states produced.…”