Coherent Quantum Control of S₂ leftrightarrow S₁ Internal Conversion in Pyrazine via S₀ to S₂/S₁ Weak Field Excitation

Coherent control of internal conversion (IC) between the first ($S_1$) and second ($S_2$) singlet excited electronic states in pyrazine, where the $S_2$ state is populated from the ground singlet electronic state $S_0$ by weak field excitation, is examined. Control is implemented by shaping the laser which excites $S_2$. Excitation and IC are considered simultaneously, using the recently introduced resonance-based control approach. Highly successful control is achieved by optimizing both the amplitude and phase profiles of the laser spectrum. The dependence of control on the properties of resonances in $S_2$ is demonstrated.