Introduction
A typical definition of the Jahn-Teller effect is that “ for any non-linear molecule in a degenerate electronic state, there exists a displacement of the nuclei along at least one non-totally symmetric normal coordinate, that gives rise to a distortion of the molecular geometry with a concomitant lowering of the energy”. To quantitatively understand this effect in molecules has always been a real challenge both computationally and experimentally. However, significant progress has taken place allowing for a better characterization of the molecular systems subject to the Jahn-Teller effect. (For general background on the Jahn-Teller effect see the review articles publications 266, 294 and 310.
Experimentally the information about the coupling between the electronic and vibrational degrees of freedom in the molecule can be obtained via vibrational spectroscopy, such as medium resolution laser induced florescence (LIF) to study vibronic structure in the excited electronic state, and dispersed florescence technique (DF) to study the structure of the ground electronic state. Additionally, the analysis of the rotationally resolved spectra of the Jahn-Teller active states gives the information about the degree of coupling between vibronic state (spin-rotation tensor and Coriolis uncoupling terms) and other electronic states (spin-rotation terms).
Recent advances in development of quantum chemistry methods and also the rapidly growing industry of high performance workstations have allowed to approach the problem of the study of the potential energy surfaces strictly ab-initio. With the help of quantum chemistry codes (Gaussian 98/03, Aces II, Columbus) and access to computer resources at Ohio Supercomputer Center (OSC) we can explore the peculiarities of the interaction between nuclear and electronic motion in all details. Our theoretical studies on Jahn-Teller systems has been extended recently to studies of trimers of heavy atoms (Cu3, Ag3, Au3) and to the smallest alkoxy radical (CH3O).
Our basic strategy is to relate the experimental observables to the potential energy surface and by doing so we are able to extract molecular parameters directly characteristic of the Jahn-Teller effect. Our perspective is to develop adequate theoretical models that are based on the experimental observation and are able to reconstruct the complicated Jahn-Teller distorted potential energy surface (PES) of the degenerate state of the molecules.
To accelerate the process of data analysis we develop “in-house” software packages to “decrypt” experimental data in the most efficient way. These high throughput programs for data analysis are written in scientific languages like Fortran and C++ and utilize the most efficient methods for the solution of the problem. All the packages incorporate user interface for the fast visual representation of the simulation and comparison with experimental data, and also elements of the artificial intelligence for computer based spectra comparison and automated fit. Visualization of simulations is of primary importance since the space of PES parameters critically affecting the appearance of the spectrum can have 10 dimensions or more (CH3O). The analysis is even more sophisticated if both states of the observed electronic transition are distorted by Jahn-Teller activity and spin-orbit coupling. For example, applying these innovative analysis methods, recently we succeeded in the determination of the best set of parameters which reproduce all the available experimental spectra for 2E’-2E” electronic transition of silver trimer (6 traces total).
Additional
Information and Publications for Jahn-Teller Active
Radicals Studied by GOES
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Methoxy Family |
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Cadium Monomethyl |
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