Theoretic Calculation For Molecular Stark Effect And States Selection At Hexapole

Now the technique of steric effect of neutral molecules with permanent dipole moment has been applied to many fields such as molecule reaction dynamics, molecular structure analysis and detection and so on. Especially, the method of spatial focus and state selection for polar molecules by electrostatic hexapole has been used more and more in experiments such as photodissociation, molecules collision reaction and molecule deceleration. All of these experiments need to realize the molecules with certain rotational states, and even to obtain the molecules with a pure rotational state. It can be realized by the apparatus called hexapole. The hexaple is made of six long electrodes symmetrically and the electrodes are applied to positive and negative high voltage. In this thesis, we do much work in the theoretic calculation of hexaple apparatus for the purpose of the focus and state selection of molecules. Firstly we give a brief description of molecular Stark effect in an applied electric fields. In this part, we introduce the Stark effect of different types of molecules and give out the formulae of their Stark energies. Further more, we analyze the force act on the molecules as a result of the different Stark energies in the unhomogeneous electric fields so that a theoretical calculation can be performed for the molecular focus and states selection in hexapole. The electrodes section of ideal hexapole is hyperboloid. The electric fields magnitude distribution of ideal hexapole is strict homocentric circles. For the convenience of machining, the cylindrical electrodes are always used to take place of the ones with sections of hyperboloid. This leads to that the distribution of electric potential and electric fields magnitude are somewhat different compare with the ideal hexapole's. The theoretic calculation begins from dealing with the distribution of electric potential and electric fields magnitude. Successive over relaxation interative method to solve the partial differential equation are introduced in appendix. Then we solve the Laplace equation ? 2U = 0 in successive over relaxation method, and gain the mumerical resolution of distribution of potential and electric fields magnitude in hexapole. At last, the distribution formula of potential are given out by mumerical fit method as At the time that we induce the distribution formulae of electric fields magnitude by the fitted potential formulae, we find that it's false to deal with the distribution formulae of electric fields magnitude in the old approximation. And we also draw a conclusion that we must induce the distribution formulae of electric fields magnitude from the fitted distribution formulae of potential in order to give out a exactdistribution formula of electric fields magnitude in cylindrical rod approximation for hexapole as Though the formula is more complex in this means, it's not much more difficult in our calculation under an assistance of computer. In the following work of the calculation, we find that the calculation speed is not slow apparently compared with calculation in the formulae used before. We also calculate the changing law of the potential distribution formulae's coefficients when the ratio of radius of rods to the radius of hexapole changes. Compared with the result gotten before, we find some difference. The second item's monotonicity is contrary to the previous result. By analyzing the changing law, we know that the distribution of cylindrical rod approximation for hexpole electric fields is most close to the distribution of ideal hexapole when 0we can calculate as ideal hexapole simply when we manufacture the apparatus in this ratio. At the following part, we discuss and analyze this difference, and we get to know that our result is right. At last, we calculate the molecular trajectories in hexapole with the distribution formulae of electric fields magnitude that is given out by us, and get the result of focus of molecules with certain rotational states. We compare the results with ones gotten by the fomula used before and analyze the...