Imaging alignment of rotational state-selected CH₃I molecule

We experimentally and numerically investigate CH₃I molecular alignment by using a femtosecond laser and a hexapole. The hexapole provides the |111> rotational state condition at 4.5-kV hexapole rod voltage. Based on this single rotational state, an enhanced alignment degree of 0.73 is achieved. Our experimental results are in agreement with the simulation results. We experimentally obtain the ion velocity map images and show the influence of the initial rotational-state population. With the I⁺ ion images and angular distributions at different pump-probe delay time, the alignment and anti-alignment phenomena are further demonstrated. The molecules will be under field-free conditions when the laser effect disappears completely at the full revival time. Our work shows that the quantum control and spatial control on CH₃I molecules can be realized and molecular coordinate frame can be obtained for further molecular experiment.