UC Berkeley

Recent developments of isolated, sub-femtosecond light pulses generated via upconversion of commercially available 800 nm light sources have allowed for the study of chemical dynamics in the tens to few hundred attosecond (1 attosecond = 1 as = 1 x 10^-18 s) temporal domain. Electron dynamics, or motions of electrons, occur on this timescale. These dynamics govern fundamental quantum mechanical processes that have applications ranging from chemical reactions to charge transfer and beyond.

In this dissertation, an attosecond transient absorption apparatus was constructed to measure electron dynamics in atoms and molecules. Chapter 2 discusses the considerations made in building the apparatus, a description of the individual components and processes that comprise the instrument, and the current performance of the experimental system. In short, the instrument is capable of resolving dynamics as short as ~200 as in duration with photons spanning the spectral ranges of either 50-73 eV or 65-90 eV. Chapter 3 addresses the characterization techniques utilized to ensure optimal performance of the attosecond transient absorption apparatus; methods to measure laser pulse temporal durations, spatial beam profiles, extreme-ultraviolet (XUV) light pulses, and photoelectron kinetic energies are documented.

After construction of the attosecond transient absorption apparatus, preliminary experiments were conducted to lay the groundwork for studies of electron dynamics in molecular systems. Chapter 4 documents a method by which integrated XUV absorption cross section ratios of atoms and molecules may be determined; this information is necessary for quantifying branching ratios of chemical reactions using XUV transient absorption spectroscopy. In the conclusion, chapter 5 characterizes two molecular systems, CH₃Br and Br₂, which may be ionized by strong fields potentially to produce a superposition of two electronic states, thus forming an electronic wavepacket that may be studied via attosecond transient absorption spectroscopy. Such systems provide a framework for understanding simple electronic wavepackets in molecules before progressing to studying these dynamics in more complicated systems.