Multiphoton Dissociation of Polyatomic Molecules

Abstract

The dynamics of infrared multiphoton excitation and dissociation of SF, has been investigated under collision free conditions by a crossed laser-molecular beam method.In order to understand the excitation mechanism and to elucidate the requirements of laser intensity and energy fluence, a series of experiments have been carried out to measure the dissociation yield dependences on energy fluence, vibrational temperature of SF & , the pulse duration of the C0 2 laser and the frequency in both one and two laser experiments.Translational energy distributions of the SF,-dissociation product measured by time of flight and angular distributions and the dissociation lifetime of excited SF 6 as inferred from the observa tion of secondary dissociation of SF g into SF.and F during the laser pulse suggest that the dynamics of dissociation of excited v u understand multiphoton dissociation of polyatomic molecules.Yuan Lee is the person most responsible for the success of the experiments that, culminated in this thesis.When I did not know what part of the molecular beam apparatus had gone awry, Yuan was there to help find and fix the problem.I most appreciate his incessant search for experimental results, his quick comprehension and analysis of those results, and his synthesis of a new framework in which to view the experimental results.Ron Shen was also intimately involved in these experiments and I thank him for giving me a clearer understanding of the excitation process in multiphoton dissociation.By his patience in pointing out how my explanations were confused and muddled, he helped to make this thesis into as readable a document as it is.I owe him a debt of gratitude for making me a better writer.Mike Coggiola first introduced me to the crossed molecular beam technology that was vital for doing these experiments.Together with Ed Grant, we made the first tentative steps toward understanding SF, multiphoton dissociation, which is the subject of Chapter II.Ed Grant performed many calculations that convinced me of the importance of the rate equation model for understanding the roles of laser intensity and energy fluence in multiphoton dissociation, the subject of Chapter III.-V-Aasmund Sudbtf is primarily responsible for much of the analysis of the many angular and time-of-flight distributions that we obtained during 1977.He combined the traits of efficiency and diligence at work with a good sense of humor.Happily these traits were also apparent in Doug Krajnovich during our search to unravel the mysteries of C-FgCl multiphoton dissociation.Anna Giardini-Guidoni provided pleasant and valuable assistance during three months of study of C 2 FgCl.I wish to thank Ann Weightman for her essentially error