Imaging The Alignment Of Rotational State-selected CH₃I Molecule

In modern physics experiment, controlling the spatial alignment andorientation of molecules is more and more interested by the researchers,because the success of alignment and orientation of molecules is a premisethat the researchers study molecular reaction dynamics and molecularcomplex structure, since1990s, the researchers began to take advantage ofthe strong static electric field and the pulsed intense laser to align and orientmolecules, especially the rapid development of femtosecond laser, thefemtosecond laser can induce molecules along the polarization direction ofthe laser beam propagates, which is characterized by the use offemtosecond laser pulse width is much smaller than the rotation cycle ofthe molecule, the molecular applying (kick) the role of a "fast kick", thenthe laser effect disappears, eventually the molecule can be under free fieldCondition, this method is non-adiabatic collimation in order to get a betteralignment of molecules, began using a strong electric field and the methodof combining the femtosecond laser collimation molecule experiments.In this thesis, we combine the hexapole electrostatic field withfemtosecond laser to study the alignment of methyl iodide (CH3I). Firstly，Taking advantage of hexapole to select different rotational states of methyl iodide, then the one that we interest can be selected. Secondly, in theory,we simulate the alignment of methyl iodide in both cases, the one is underthe case of hot average, the other is the molecule of rotational state-selected.Then the conclusion is that the molecule of rotational state-selection canenhance the alignment which can be confirmed. Finally, by means ofpump-probe to study, the pump one aligns the molecule of rotational state-selected, the probe one ionizes the molecule, after analyzing data, we canclearly see the free evolution of femtosecond laser acting on the molecules,we prove that femtosecond laser can enhance the alignment of molecule,then by the means of Velocity Map Imaging, comparing the images intheory with those in experiment, we can clearly find the nonadiabaticalignment.