Date of Award

Spring 1-1-2012

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry & Biochemistry

First Advisor

David M. Jonas

Second Advisor

G. Barney Ellison

Third Advisor

Niels H. Damrauer

Fourth Advisor

Rex T. Skodje

Fifth Advisor

Margaret M. Murnane

Abstract

Degenerate femtosecond pump-probe transient absorption measurements are presented of hot carrier dynamics following above band-edge absorption in colloidal lead sulfide quantum dots. A transient bleach is only found when pumping to a satellite valley. When pumping in the main valley no transient bleach is seen with 20-25 fs pulses, indicating hot carrier dephasing occurs in 5 fs or less. The signal at long times is ~300 times smaller than would be expected from a two level system, indicating systematic excited state absorption. Based on this data, arguments based on bulk band structure and scattering length indicate hot electrons are essentially bulk-like until cooling to quantum confined states.

Femtosecond electronic dynamics are also studied theoretically for model Hamiltonians developed to model near-degenerate states in molecules or molecular dimers. Particular emphasis is placed on the case of weak nonadiabatic coupling when the electronic energy gap is close to one vibrational quantum of energy. A visualization scheme is developed for plotting nonadiabatic wavefunctions with an explicitly shown vibrational wavefunction and coordinate-dependent coloring which indicates both electronic composition and overall wavefunction sign. Nonadiabatic eigenstates are found to display a vibrationally nodeless character, indicating large-amplitude oscillations between zero-order electronic basis states.

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