Our research focuses on experimental probes of the electronic structure and time-resolved dynamics of atomic, molecular and cluster anions. Our experiments offer an in-depth look at chemical structure and reactivity, made possible by photoelectron imaging spectroscopy.

See NSF Research Nugget:


(requires PowerPoint 2002 or later - WILL NOT work properly with earlier versions)

Our goal is to develop photoelectron imaging into a comprehensive method for studies of the electronic structure of anions and its evolution in chemical reactions.

One of the cornerstones of our research program is the development of new experimental methodologies, such as the application of femtosecond photoelectron imaging to negative ions. In this approach, the integration of several techniques from different areas experimental physics and chemistry allows us to reach new levels of capabilities.

Negative-ion photoelectron imaging spectrometer. Our home-build apparatus is shown schematically in the figure:


It consists of a pulsed ion source, a time-of-flight ion mass spectrometer, and a photoelectron imaging assembly.

Photoelectron images are recorded using a velocity-mapping electrostatic lens, by projecting the photoelectrons on a position-sensitive detector. From the resulting image a complete 3D velocity distribution, including the speed and angular distributions, can be uniquely reconstructed. The radial or speed distributions represent the photoelectron energy spectra. The angular distributions reflect the electronic wave function symmetry and convey information about the parent atomic or molecular orbitals.

For example, the figure below shows one of the very first photoelectron images recorded in our laboratory. It was obtained in the photodetachment of I^- at 267 nm with the laser polarized vertically in the image plane:

We use cluster anions as model micro-solutions - a platform for the studies of elementary chemical processes in condensed environments. We study the effects of intermolecular interactions on the electronic wave functions and, therefore, chemical bonding.

Time-Resolved (Femtosecond) Photoelectron Imaging. The most exciting aspect of our research is the use of time-resolved photoelectron imaging to obtain a unique perspective of reaction dynamics. The application of photoelectron imaging in conjunction with ultrafast pump-probe techniques enables us to monitor the evolution of electronic structure along reactive pathways, emphasizing the evolving electronic wave functions, not just the energy eigenvalues.

We are interested in a wide range of chemical processes transpiring on timescales from 100 fs to 100 ps. We are particularly interested in cases involving internal conversion or dissociation via a conical intersection or avoided crossing, as straightforward opportunities to study nonadiabatic dynamics.

We use 100 fs laser pulses to initiate reactive events in molecular and cluster anions and probe the evolving electronic structure by photodetaching electrons at variable pump-probe delays, recording time-dependent photoelectron images of the reaction. The following figure gives a schematic diagram of our femtosecond amplified tunable laser system (Spectra Physics, Inc). Click on the figure to see a photo.

In addition to the experiments, important aspects of our research are electronic structure calculations and the advancement of theory of molecular anion photodetachment with respect to the photoelectron angular distributions.

• "Dynamic molecular interferometer: Probe of inversion symmetry in I₂^- photodissociation", R. Mabbs, K. Pichugin, and A. Sanov, J. Chem. Phys., in press (2005).

• "Time-resolved imaging of the reaction coordinate", R. Mabbs, K. Pichugin, and A. Sanov, J. Chem. Phys. 122, 174305 (2005).

• "Photoelectron anisotropy and channel branching ratios in the detachment of solvated iodide cluster anions", R. Mabbs, E. Surber, and A. Sanov, J. Chem. Phys. 122, 054308 (2005).

• "Time-resolved electron detachment imaging the I^– channel in I₂Br^– photodissociation", R. Mabbs, K. Pichugin, E. Surber, and A. Sanov, J. Chem. Phys. 121, 265-272 (2004).

• "Cluster anions: Structure, interactions, and dynamics in the sub-nanoscale regime", Andrei Sanov and W. Carl Lineberger, Phys. Chem. Chem. Phys. 6, 2018-2032 (2004).

• "An experimental manifestation of distinct electronic-structural properties of covalent dimer anions of CO₂ and CS₂", Richard Mabbs, Eric Surber, and Andrei Sanov, Chem. Phys. Lett. 381, 479-485 (2003).

• "Imaging of Direct Photodetachment and Autodetachment of (OCS)₂^-: Excited-State Dynamics of the Covalent Dimer Anion", Eric Surber and Andrei Sanov, Phys. Rev. Lett. 90, 093001 (2003).

• "Probing the Electronic Structure of Small Molecular Anions by Photoelectron Imaging”, Eric Surber, Richard Mabbs, and Andrei Sanov, J. Phys. Chem. A 107, 8215-8224 (2003).

• "Photoelectron Imaging of Negative Ions: Atomic Anions to Molecular Clusters", Richard Mabbs, Eric Surber, and Andrei Sanov, Analyst 128, 765-772 (2003).