Ultrafast lasers allow for the investigation of chemical reactions on their own natural time scale, much as a strobe light allows the visualization of rapid motion on a camera. The strong electric fields of amplified ultrafast lasers can be used not only to observe a chemical reaction, but also to control it. In this thesis, we present observations of molecular dissociation dynamics and evidence of control in several small molecules. We begin with a discussion of alignment dynamics, whereby field-free alignment is initiated in a sample of gas-phase molecules prior to ionization and dissociation. This enhances the ionization effectiveness of subsequent laser pulses, particularly for diatomic molecules such as N2 and O2, as the molecular axis can be aligned with the laser polarization.
We continue with a discussion of dissociation dynamics in a family of small molecules, focusing on halogen-substituted methanes (halomethanes). Halomethanes are small enough to allow for detailed electronic structure calculations, while being large enough to be chemically relevant and offer opportunities for selective dissociation. We find that dissociation in halomethanes is controlled by the development of transient ionic resonances, which can be accessed by a weak probe pulse following the ionizing pump pulse. These dynamic resonances create strong oscillatory behavior in the experimental ion yields, which can be modeled by wave packet calculations on ab initio potential energy surfaces. We find excellent quantitative agreement between the calculations and the experimental measurements, yielding a detailed understanding of the dissociation dynamics of some members of the halomethane family, including CH2BrI. Ongoing work focuses on better understanding differences between members of the molecular family. This understanding may have implications for control and dissociation dynamics in larger, more complicated molecules.
|School:||State University of New York at Stony Brook|
|School Location:||United States -- New York|
|Source:||DAI-B 70/05, Dissertation Abstracts International|
|Subjects:||Physical chemistry, Molecular physics, Optics|
|Keywords:||Coherent control, Dynamic resonance, Halomethanes, Molecular alignment, Molecular dissociation, Ultrafast lasers|
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