Laser Induced Molecular Dissociation

Sam Roland

Supervisor: Itzik Ben-Itzhak

Kansas State University Physics Department  REU Program, sponsored by NSF

This program is funded by the National Science Foundation through grant number PHY-0851599.


Welcome to my webpage!  This page summarizes my experience doing research for the Summer 2009 at Kansas State University in the James R. Macdonald Laboratory

Summary Statement: My research is to understand how certain diatomic molecular ions (CO+ and NO+) interact with a short pulse laser beam. In particular I am analyzing two possible interactions: dissociative ionization and non-dissociative ionization. Ionization occurs when the source ion looses an electron (ex: non-dissociative ionization CO+ + nћω → CO++ + e-). Dissociation occurs when the two nuclei separate (ex: CO+ + nћω → C+ + O+ + e- ). The experimental apparatus allows us to separate particles with different charge-to-mass ratio in time and space, thus the two types of ionization can be analyzed separately.

Project Goals: My aim is to count the number of times each process occurs for a given period of time and laser intensity. I am interested in the effect of laser intensity on the relative frequency of dissociative and non-dissociative ionization. Furthermore I would like to understand any observed differences between the ionization of CO+ and NO+. This project is also a demonstration of our ability to detect both types of ionizations from a single ion source.

Experimental Apparatus: The laser beam is focused by a parabolic mirror to a point inside the spectrometer. The ion beam passes through the spectrometer where it interacts with the laser. The resulting fragments then pass through a deflector before reaching the particle detector. Click on the image blow to learn more about each major component of the experimental setup.



Results and Interpretation: Analysis of data collected from seven different laser intensities yielded the number of non-dissociative ionization events [CO++], the number of dissociative ionization events [C++O+] and the ratio of the two events [CO++]/[C++O+] for each laser intensity. Preliminary results show a higher rate of total ionization in CO+ than NO+. Furthermore I observed less dissociative ionization of NO+ than CO+ but approximately the same rate of non-dissociative ionization. These results may be accounted for by appealing to the potential energy curves of these various ions. The lower total ionization rate in NO+ may be due to the fact that the difference in potential energy between the ground states of CO+ and CO++ is smaller than the difference between NO+ and NO++. The smaller rate of dissociative ionization of NO+ may be explained by the deep potential well in the NO++ potential curves compared to the CO++ potential curves. Furthermore I observed that the kinetic energy release distribution of the breakup CO+ C++O+ was qualitatively similar the kinetic energy release distribution of the breakup CO++ C++O+. The same observation was made for the breakup NO+ N++O+ and NO++ N++O+. These results suggest that the primary ionization mechanism was direct ionization from CO+ (or NO+) states to CO++ (or NO++) states.


Potential Energy Curves:



Final Report

About Me:  Rising junior Physics and Math major at Cornell University

Useful Links: 

American Physical Society Statements on Ethics

American Institute of Physics