Electron attachment to closed-shell molecules is a gateway to various important processes in the gas and condensed phases. The properties of an electron-attached state, such as its energy and lifetime as well as the character of the molecular orbital to which the electron is attached, determine the fate of the anion. In this experimental and theoretical study of copper and silver fluoride anions, we introduce a  new type of metastable anionic state. Abrupt changes in photoelectron angular distributions point to the existence of autodetaching states. Equation-of-motion coupled-cluster singles and doubles calculations augmented by a complex absorbing potential identify some of these states as Σ and Π dipole-stabilized resonances, a new type of shape resonance. In addition, these molecules support valence and dipole-bound states and a Σ resonance of charge-transfer character. By featuring five different types of anionic states, they provide a vehicle for studying fundamental properties of anions and for validating new theoretical approaches for metastable states.

A photodissociative study of CuO2− is presented using a combination of energy and time domain photoelectron spectroscopy. Ion source conditions are used that solely produce linear OCuO−. Photodissociation of this isomer to produce Cu− + O2 is conclusively demonstrated at wavelengths between 765 and 340 nm. Nanosecond pulsed photoexcitation at wavelengths shorter than 340 nm produces single photon detachment transitions from the first excited state of CuO2−. At longer wavelengths narrow Cu− fragment transitions are observed as a result of a sequential two photon process. In addition, the longer wavelengths produce a weak, broad two photon dependent signal, the result of detachment of the dissociating linear isomer. Time resolved pump–probe measurements reveal a long timescale growth (up to 150 ps) of the Cu− fragment yield, consistent with the unfavorable starting geometry for the dissociative process and indicating a potential energy surface which has one or more substantial barriers to dissociation.

The use of photoelectron angular distributions to provide structural details of cluster environments is investigated. Photoelectron spectra and angular distributions of I–·(H2O)2 and I–·(CH3CN)2 cluster anions are recorded over a range of photon energies. The anisotropy parameter (β) for electrons undergoes a sharp change (Δβmax) at photon energies close to a detachment channel threshold. I–·(H2O)2 results show the relationship between dipole moment and Δβmax to be similar to that observed in monosolvated I– detachment. The Δβmax of the 4.0 eV band in the I–·(CH3CN)2 photoelectron spectrum suggests a dipole moment of 5–6 D. This is consistent with predictions of a hydrogen bonded conformer of the I–·(CH3CN)2 cluster anion [Timerghazin, Q. K.; Nguyen, T. N.; Peslherbe, G. H. J. Chem. Phys. 2002, 116, 6867–6870].

Photoelectron imaging probes both molecular electronic structure and electron molecule interactions. In the current work images were recorded for detachment from the I−·C4H5N (I−·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.

Photoelectron imaging is finding increasingly widespread use in probing electronic structure and chemical dynamics. In this tutorial review, two benchmark systems, H− and I−, are used to introduce essential concepts linking photoelectron images of negative ions with parent electronic structure. For pedagogical reasons, a qualitative approach based upon spectroscopic selection rules is emphasized in interpreting the images. This approach is extended to molecular systems, highlighting that even qualitative interpretation of results can lead to significant chemical insights.

A photodissociative study of CuO2− is presented using a combination of energy and time domain photoelectron spectroscopy. Ion source conditions are used that solely produce linear OCuO−. Photodissociation of this isomer to produce Cu− + O2 is conclusively demonstrated at wavelengths between 765 and 340 nm. Nanosecond pulsed photoexcitation at wavelengths shorter than 340 nm produces single photon detachment transitions from the first excited state of CuO2−. At longer wavelengths narrow Cu− fragment transitions are observed as a result of a sequential two photon process. In addition, the longer wavelengths produce a weak, broad two photon dependent signal, the result of detachment of the dissociating linear isomer. Time resolved pump–probe measurements reveal a long timescale growth (up to 150 ps) of the Cu− fragment yield, consistent with the unfavorable starting geometry for the dissociative process and indicating a potential energy surface which has one or more substantial barriers to dissociation.

Photoelectron imaging is finding increasingly widespread use in probing electronic structure and chemical dynamics. In this tutorial review, two benchmark systems, H− and I−, are used to introduce essential concepts linking photoelectron images of negative ions with parent electronic structure. For pedagogical reasons, a qualitative approach based upon spectroscopic selection rules is emphasized in interpreting the images. This approach is extended to molecular systems, highlighting that even qualitative interpretation of results can lead to significant chemical insights.