Direct and Indirect Detachment in the Iodide−Pyrrole Cluster Anion: The Role of Dipole Bound and Neutral Cluster States

Abstract

Photoelectron imaging probes both molecular electronic structure and electron molecule interactions. In the current work images were recorded for detachment from the I(-) x C(4)H(5)N (I(-) x pyrrole) cluster anion at wavelengths between 360 and 260 nm. The direct detachment spectra show strong similarities to those of I(-), although a strong solvent shift, broadening and some structure is observed. A nondirect, dissociative or autodetachment feature is also observed over a range of wavelengths. Ab initio calculations identify several local minima associated with neutral and anion isomers. Energy and Franck-Condon arguments are used to assess the role of these in the detachment process. The cluster anion structure is essentially an I(-) atomic anion in the presence of a neutral pyrrole molecule. The spectral structure arises due to interactions in the open shell neutral cluster residue resulting from detachment. The indirect detachment feature arises through the formation of an intermediate dipole bound cluster anion state which subsequently dissociates. The energy dependence of this channel (observed over a 0.6 eV range of photon energies) is discussed in terms of the wide amplitude motions associated with the van der Waals modes of the cluster anions.

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

“…The location of the channel II threshold is approximately 0.94 eV above the channel I threshold, although the precise separation between the two channels is complicated by the interaction of the molecular moiety with the iodine atom. 5,23 The branching ratio of photoelectrons detached via the two channels (Figs. 2 and 3 right hand ordinate, open circles) shows the onset of channel II.…”

“…25,26 However, comparison with free I − detachment at excitation energies away from the channel II threshold suggests that under those conditions there is only a minor effect on the angular distribution. [4][5][6] To date, only I − · CH 3 Br and I − · CH 3 I PADs have been observed to show a strong deviation from those of I − detachment at photon energies more than 100 meV below the channel II threshold. [2][3][4]9 These deviations are largely attributable to the effect of a low-lying anionic σ * state associated with the methyl halide molecule rather than the long range electrondipole interaction.…”

“…[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. Subsequently, we will use the labels channel I and channel II to refer to transitions correlating to the production of [I( 2 P 3/2 ) + X + e − ] and [I( 2 P 1/2 ) + X + e − ], respectively.…”

Vibronic coupling in the superoxide anion: The vibrational dependence of the photoelectron angular distribution

“…58,[63][64][65][66][67][68] In these cases, the change in ␤ can be explained through consideration of the dominant long range term in the potential, the centrifugal term. The free electron wave can be represented as a superposition of partial angular momentum waves for which we will use the symbol ᐉЈ ͑=ᐉ Ϯ 1͒ to allow distinction from the parent orbital angular momentum quantum number ᐉ.…”

Photoelectron Angular Distributions as Probes of Cluster Anion Structure: I–·(H2O)2 and I–·(CH3CN)2

“…The rapid change in the A channel β parameter at photon energies near the channel B threshold (Figure 3) is not consistent with Cooper−Zare direct detachment behavior. Instead the behavior is caused by a dipole-bound-like state (by analogy with previous work on monosolvated cluster anions) 9. 16,17 Dipole bound anion states are supported by dipole moments in excess of 2.5 D 18,19 and have been subject to extensive studies by (among others) Jordan and co-workers.…”