Christopher L. Adams

Low-energy photoelectron imaging spectroscopy of nitromethane anions : Electron affinity, vibrational features, anisotropies, and the dipole-bound state

We present low-energy velocity map photoelectron imaging results for nitromethane anions. The photoelectron spectrum is interpreted with the aid of ab initio theory and Franck-Condon factor calculations. We obtain a new value for the adiabatic electron affinity of nitromethane of (172+/-6) meV and observe the dipole-bound state of nitromethane. The photoelectron angular distributions of the observed features are discussed in the context of threshold laws for photodetachment.

Vibrational Autodetachment-Intramolecular Vibrational Relaxation Translated into Electronic Motion

If a negative ion has vibrational energy in excess of the binding energy of its most weakly bound electron, the anion can undergo vibrational autodetachment, similar to thermionic emission. When this effect occurs after targeted infrared excitation of a specific vibrational mode in the anion, it encodes information on the intramolecular vibrational relaxation processes that take place between excitation and electron emission. We present examples on how vibrational autodetachment can be used to obtain infrared spectra of molecular anions, and we discuss how a vibrational autodetachment photoelectron spectrum can be modeled, using vibrational autodetachment after excitation of CH stretching modes of nitromethane anions as a case study.

Infrared spectroscopy of hydrated naphthalene cluster anions

We present infrared spectra of mass-selected C(10)H(8)(-)·(H(2)O)(n)·Ar(m) cluster anions (n = 1-6) obtained by Ar predissociation spectroscopy. The experimental spectra are compared with predicted spectra from density functional theory calculations. The OH groups of the water ligands are involved in H-bonds to other water molecules or to the π system of the naphthalene anion, which accommodates the excess electron. The interactions in the water network are generally found to be more important than those between water molecules and the ion. For 2 ≤ n ≤ 4 the water molecules form single layer water networks on one side of the naphthalene anion, while for n = 5 and 6, cage and multilayer structures become more energetically favorable. For cluster sizes with more than 3 water molecules, multiple conformers are likely to be responsible for the experimental spectra.

Photoelectron imaging spectroscopy of nitroethane anions.

We present low-energy velocity map photoelectron imaging results for bare and Ar solvated nitroethane anions. We report an improved value for the adiabatic electron affinity of nitroethane of (191 ± 6) meV which is used to obtain a C-NO(2) bond dissociation energy of (0.589 ± 0.019) eV in nitroethane anion. We assign a weak feature at (27 ± 5) meV electron binding energy to the dipole-bound anion state of nitroethane. Photoelectron angular distributions exhibit increasing anisotropy with increasing kinetic energies. The main contributions to the photoelectron spectrum of nitroethane anion can be assigned to the vibrational modes of the nitro group. Transitions involving torsional motion around the CN bond axis lead to strong spectral congestion. Interpretation of the photoelectron spectrum is assisted by ab initio calculations and Franck-Condon simulations.

Photoelectron spectroscopy of 1-nitropropane and 1-nitrobutane anions

We present low-energy velocity map photoelectron imaging results for bare and Ar-solvated 1-nitropropane and 1-nitrobutane anions. We report the adiabatic electron affinity of 1-nitropropane as (223 ± 6) meV and that of 1-nitrobutane as (240 ± 6 meV). The vertical detachment energies of these two species are found to be (0.92 ± 0.05) and (0.88 ± 0.05) eV, respectively. The photoelectron spectra are discussed in the framework of Franck-Condon simulations based on density functional theory. We observe unusual resonances in the photoelectron spectra of both ions under study, whose kinetic energy is independent of the photon energy of the detaching radiation. We discuss possible origins of these resonances as rescattering phenomena, consistent with the experimental photoelectron angular distributions.