| Current Research: The energy of a molecule can be expressed as a function of the position of the atoms within it. The degrees of freedom a linear molecule has is 3N-6, where N is the number of atoms; therefore the corresponding potential energy surface (PES) has this many dimensions. This surface will have features such as minima and saddle points.
If excited electronic states are taken into consideration, more than one PES can co-exist. These may be accessed via photoexcitation of the ground state. Movement confined to just one PES is termed adiabatic, whilst movement between two PESs is termed non-adiabatic.
Regions where two PESs meet is termed a "conical intersection" (CI). These play an important role in ultrafast relaxation processes. This relaxation route can compete with other slower relaxation methods such as fluorescence. Knowledge of CI locations may be used to improve the contrast of various biomolecular tools that utilise fluorescence; for example one may be able to frustrate CI relaxation paths.
Conventional quantum mechanical (QM) approaches such as CASSCF for probing the multiple PES landscapes for CIs prove too computationally expensive for large biomolecular systems. Mark is currently investigating a cheaper, statistical QM/MM approach for locating CI regions. This involves calculating the ground to excited state energy gap fluctuations of a molecule's molecular dynamics trajectory. He is examining the possibility that the general location of a CI maybe ascertained by examining vibrational modes from the Fourier decomposition of the the energy gap fluctuations. |
