Ionization And Dissociation Study Of CH₃I In Femtosecond Laser Field By Velocity Map Imaging

Velocity map imaging technique has been fast developed in the past decades. The most obviously characteristic for this technique is visual ,convenient ,accurate。CH3I molecules, whether from experiment or theory, people did a lot of research, and got much information on this molecule, the molecule with rich information for our new equipment has brought a lot of easy calibration.The first chapter introduces the development history of femtosecond laser and the application in various fields. This chapter also introduces the production, development, and its characteristics of velocity map imaging.The second chapter introduces Velocity map imaging technique based on theory, including the principle of ion lens, the principle of time of flight mass spectrometry, processing images of anti-Abel transform in math, the analysis of anisotropic parameters which we got。The third and the fourth chapter describes the experimental equipment,experimental results and data analysis. At first introduced the device, process of velocity imaging, and some of the experimental parameters of the apparatus. Then I got I+ molecule of the velocity image and angle distribution in three different light intensities with Laser wavelength 800nm, pulse width 90fs, repetition rate of 10Hz, found molecular fragments of velocity images in the first two light intensities are the almost same, There are two different speed channel. In the most strong of the light intensity, not only got the velocity image of I + ions, but also got the velocity image of I 2+ ions. The result has been analyzed is the relatively low speed comes from the two I+ parent ion dissociation, high speed comes from trivalent parent ion dissociation. We get different angular distribution in different light intensities and found angle distributions are much the same, so we can infer that it is the geometric alignment mechanism.