The quantum control of the isomerisation of azomethane and a 10-membered
dibenzoazo crown ether (referred to as 02N2) was studied for the inversion
and torsional coordinates. Density functional theory was used to generate the ground (S₀ ) and first excited (S₁) electronic state potantial energy functions required to simulate the wavepacket dynamics. Laser control pulses were generated manually by observation of the wavepacket dynamics, and these were subsequently refined by using optimal control theory.
For azomethane, greater isomerisation control is possible along the torsional isomerisation coordinate than along the inversion coordinate. Control along the inversion coordinate is hindered by the existence of a potential barrier on the S1 potential energy function, and hence a complicated 4-pulse sequence is required to overcome it. Furthermore the control of azomethane isomerisation along both coordinates is limited by the small transition dipole moment coupling the S₀ and S₁ electronic states.
The topology of 02N2's S₁ potential energy surface favours the torsional
trans → cis isomerisation channel, where again an energy barrier is observed
along the S₁ inversion pathway. However, a greater yield is observed along the inversion pathway utilising a 4-pulse sequence since the locality of the
wavepacket is easier to maintain along this coordinate, as opposed to the
periodic torsional coordinate.
Finally, in chapter 6, the effect of environmental dissipation on the laser control of a model isomerisation system is investigated using the Caldeira-Leggett quantum master equation in Wigner phase space. As expected, energy dissipation and decoherence have a negative effect on the amount of quantum control possible, and the effect increases with respect to the size of the friction coefficient η.