Tracing Ultrafast Molecular Electronic Energy Transfer in Real Time and Space

Document Type




Conference Title

13th International Conference on Quantum Chemistry


Helsinki, Finland

Conference Dates

June 22-27, 2009

Date of Presentation



We study of the movement of energy between molecules and an environment. Understanding energy transfer after excitation has enormous relevance to biological processes, such as photosynthesis, as well as being of purely fundamental interest. A new channel for decay of an electronic excitation, called intermolecular Coulombic decay (ICD), was theoretically predicted more than a decade ago [1]. Since then, this process has been measured in several experiments, notably, in cold atomic clusters [2]. In the first step of ICD, a molecule which is ionized from the inner valence level is left in a state that is too low in energy to autoionize (as in the Auger process), and photoemission is very slow. In ICD, this excitation decays by ionizing a neighbor from its valence level. This process is distinguished by the participation of more than one chemical center. It therefore occurs at much lower energies, by virtue of the separation of the two final charges. It is also fast and efficient, especially given the large number of possible neighbors, and since transition into a continuum of potential final states ensures that the transfer is always at resonance. The process is generally much faster than nuclear dynamics. It has recently been observed that such energy transfer and electron emission can also occur following inner-valence excitation of the first molecule [3], rather than ionization; this is the resonant ICD (RICD) process. This process leaves only one final ionic site, has the potential to be more common in nature, and is the focus of this present work. These processes are also interesting because excitation is easier to control in the laboratory than ionization. The methodology we use has already been tested on the ICD process [4], where in-house Green’s function techniques developed over the past few decades (the algebraic diagrammatic construction [5]) were used to construct the effective quasi-particle (1-hole) Hamiltonian, applicable to the system after the initial ionization. Applying this machinery presently to the particle-hole (polarization) propagator, we can watch excitation energy move, extracting observables such as timescales. The short iterative Lanczos time propagator is applied, in order to compute the electron dynamics in real time and space. Descriptive animations of the quasi-particle (particle-hole) motion during the process can be produced.

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