The overlooked role of excited anion states in NiO2- photodetachment.

Photodetachment spectra of anionic species provide significant insights into the energies and nature of ground and excited states of both the anion and resultant neutral molecules. Direct detachment of the excess electron to the continuum may occur via formally allowed or forbidden transitions (perhaps as the result of intensity borrowing through vibronic coupling). However, alternate indirect pathways are also possible and often overlooked.

Dipole effects in the photoelectron angular distributions of the sulfur monoxide anion.

Photoelectron angular distributions (PADs) in SO photodetachment using linearly polarized 355 nm (3.49 eV), 532 nm (2.33 eV), and 611 nm (2.

Role of the Electron-Dipole Interaction in Photodetachment Angular Distributions.

The importance of including long-range electron-molecule interactions in treatments of photodetachment and/or photoionization is demonstrated. A combined experimental and computational study of CN detachment is presented in which near threshold anisotropy parameters (β) are measured via photoelectron imaging. Calculated β values, based on an EOM-IP-CCSD/aug-cc-pVTZ Dyson orbital, are obtained using free-particle and point dipole models.

Spectroscopy of temporary anion states: Renner-Teller coupling and electronic autodetachment in copper difluoride anion.

Photoelectron angular distributions determined in small energy increments between 3.522 and 3.650 eV reveal distinctly different detachment mechanisms within the CuF(X Σ) → linear CuF(X Σ) + e band.

Characterization of the vibrational properties of copper difluoride anion and neutral ground states via direct and indirect photodetachment spectroscopy.

Photoelectron spectra of CuF are reported at wavelengths 310 nm, 346.6 nm, and 350.1 nm, obtained via velocity map imaging.

Photoelectron Imaging of Anions Illustrated by 310 Nm Detachment of F.

Anion photoelectron imaging is a very efficient method for the study of energy states of bound negative ions, neutral species and interactions of unbound electrons with neutral molecules/atoms. State-of-the-art in vacuo anion generation techniques allow application to a broad range of atomic, molecular, and cluster anion systems. These are separated and selected using time-of-flight mass spectrometry.

Channel branching ratios in CHCN photodetachment: Rotational structure and vibrational energy redistribution in autodetachment.

We report photoelectron spectra of CHCN, recorded at photon energies between 13 460 and 15 384 cm, which show rapid intensity variations in particular detachment channels. The branching ratios for various spectral features reveal rotational structure associated with autodetachment from an intermediate anion state. Calculations using equation-of-motion coupled-cluster method with single and double excitations reveal the presence of two dipole-bound excited anion states (a singlet and a triplet).

Same but Different: Dipole-Stabilized Shape Resonances in CuF(-) and AgF(.).

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.

The effect of the dipole bound state on AgF⁻ vibrationally resolved photodetachment cross sections and photoelectron angular distributions.

The first photoelectron spectra of AgF(-) are recorded over the energy range 1.61-1.85 eV using the velocity map imaging technique.

Photoelectron angular distributions as probes of cluster anion structure: I(-)·(H2O)2 and I(-)·(CH3CN)2.

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.

Photodetachment and photodissociation of the linear OCuO- molecular anion: energy and time dependence of Cu- production.

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.

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

Photoelectron imaging results are presented for I(-)[middle dot]X cluster anions (X = CO(2), C(4)H(5)N [pyrrole], (CH(3))(2)CO, CH(3)NO(2)). The available detachment channels are labeled according to the neutral iodine atom states produced (channel I ≡ (2)P(3/2) and channel II ≡ (2)P(1/2)). At photon energies in the vicinity of the channel II threshold these data are compared to previously reported results for I(-)[middle dot]X (X = CH(3)CN, CH(3)Cl, CH(3)Br, and H(2)O).

I(-)·(CH3I)2 photoexcitation: the influence of dipole bound states on detachment and fragmentation.

We present the results of a photoelectron imaging study of the I(-)·(CH(3)I)(2) cluster anion over excitation wavelengths 355-260 nm. The resulting spectra and photoelectron angular distributions (PADs) suggest extensive electron-molecule interaction following photoexcitation. Fragmentation channels are observed subsequent to excitation between 355 and 330 nm.

Near threshold Cl(-)·CH3I photodetachment: apparent 2P1/2 channel suppression and enhanced 2P3/2 channel vibrational excitation.

Cl(-)·CH(3)I cluster anion photoelectron images are recorded over a range of detachment wavelengths in the immediate post threshold region. The photoelectron spectral features fall into two categories. A number of weak, photon energy dependent transitions are observed and attributed to atomic anion fragmentation products.

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

We present a comprehensive photoelectron imaging study of the O(2)(X  (3)Σ(g)(-),v(')=0-6)←O(2)(-)(X  (2)Π(g),v(")=0) and O(2)(a (1)Δ(g),v(')=0-4)←O(2)(-)(X  (2)Π(g),v(")=0) photodetachment bands at wavelengths between 900 and 455 nm, examining the effect of vibronic coupling on the photoelectron angular distribution (PAD). This work extends the v(')=1-4 data for detachment into the ground electronic state, presented in a recent communication [R. Mabbs, F.

I(-)⋅CH(3)X (X=Cl,Br,I) photodetachment: The effect of electron-molecule interactions in cluster anion photodetachment spectra and angular distributions.

The electron kinetic energy dependence of the photoelectron spectra and angular distributions of I(-)⋅CH(3)X (X=Cl,Br,I) cluster anions are measured via velocity mapped imaging at wavelengths between 350 and 270 nm. Processes analogous to those encountered in free CH(3)X-electron interactions are revealed. In particular, the presence and energies of resonances associated with a low lying σ(∗) state have a marked effect on the results of I(-)⋅CH(3)X photoexcitation.

Threshold effects in I- x CH3CN and I- x H2O cluster anion detachment: the angular distribution as an indicator of electronic autodetachment.

I(-) x H(2)O and I(-) x CH(3)CN cluster anion photodetachment properties (photoelectron spectra and angular distributions) are recorded via velocity mapped photoelectron imaging for wavelengths between 270 and 340 nm, in small energy increments. These are compared with free I(-) detachment results and reveal the presence of a sharp change in the angular distribution for the (2)P(3/2) spin orbit channel in the vicinity of the (2)P(1/2) threshold. The effect is seen at this threshold in the I(-) x H(2)O cluster anion and just below threshold for I(-) x CH(3)CN.

The effect of intracluster photoelectron interactions on the angular distribution in I(-)*CH(3)I photodetachment.

I(-) and I(-)*CH(3)I velocity mapped photodetachment images are recorded over wavelengths between 270 and 370 nm. Spectral similarities, in conjunction with ab initio calculations show that the cluster anion comprises an atomic iodide anion moiety solvated by a relatively unperturbed CH(3)I molecule. Between 340-370 nm and at 280 nm, free I(-) is produced via a process analogous to dissociative electron attachment within the cluster anion.

Direct and indirect detachment in the iodide-pyrrole cluster anion: the role of dipole bound and neutral cluster states.

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.

Photoelectron imaging: an experimental window into electronic structure.

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.

Photoelectron imaging of hydrated carbon dioxide cluster anions.

The effects of homogeneous and heterogeneous solvation on the electronic structure and photodetachment dynamics of hydrated carbon dioxide cluster anions are investigated using negative-ion photoelectron imaging spectroscopy. The experiments are conducted on mass-selected [(CO(2))(n)()(H(2)O)(m)()](-) cluster anions with n and m ranging up to 12 and 6, respectively, for selected clusters. Homogeneous solvation in (CO(2))(n)()(-) has minimal effect on the photoelectron angular distributions, despite dimer-to-monomer anion core switching.

Dynamic molecular interferometer: probe of inversion symmetry in I2(-) photodissociation.

Time-resolved photoelectron imaging of negative ions is employed to examine 780-nm dissociation dynamics of I2(-), emphasizing the effects of interference in time-resolved photoelectron angular distributions obtained with 390-nm probe. No energetic changes are observed after about 700 fs, but the evolution of the photoelectron anisotropy persists for up to 2.5 ps, indicating that the electronic wave function of the dissociating anion continues to evolve long after the asymptotic energetic limit of the reaction has been effectively reached.