Rotational State Selection Of Molecules By Electrostatic Hexapole Beam-Force

State selected neutral molecules can provide many intriguing and unique possibilities, so serious attention was paid to molecular rotational state selection. Rotational state selection can help to study and analysis the construction and detailed energy information of molecules. Rotational state selection plays a more important role in reactive inelastic inreactive inelastic collisions. Many ways can be used to get state-selected neutral molecules, for example, laser pumping inhomogeneous static electric fields, or optical fields. Especially, the method of focusing and state selection polar molecules by electrostatic hexapole field has been interested and widely applied by many researchers. In the past, hexapole apparatus just was used for polar symmetrical top molecules. We developed a small set of rotational state selection and focusing of asymmetrical top molecules by applying inhomogeneous electrostatic hexapole in these years.In this thesis, we study the focusing and rotational state selection of molecular methane iodine by homogeneous electrostatic hexapole apparatus. Electrostatic hexapole field focus up-Stark-effect polar molecules on the axis of hexapole. The interaction force depends on rotational state if neglecting hyperfine interactions. So we can get rotational state selected target by applying hexapole field. This is important for a number of experiments such as photo dissociation, photo ionization, crossed molecular beam collision, electron scattering, potential surface scattering of these molecules. For high level control freedom of molecule, hexapole state selection technique can be worked with ac-Stark effect and "brute force" technology. We choose methane iodine to be studied, for the reason that methane iodine is a classical symmetrical top molecule and t he energy spacing of rotational state is broad. The experimental apparatus for state selection using a 50 cm electrostatic hexapole field and a 800 nm, repetition rate 10 Hz femtosecond pulsed laser and a time-of-fight mass spectrometer. The focusing curves of the CH3I+ and I+ increase with the voltage of the hexapole increasing. We simulate the curve using transmission of simple rotational state from assimilation program developed in the lab with a consideration of the thermal distribution for molecular rotational state. The results compare with the experimental measured date and use for analyzing the rotational states selection by the experimental method employed.