| The work in this dissertation involves the use of strong-field photoelectron spectroscopy to investigate large polyatomic molecules.; A new spectroscopic technique, Field-Induced Resonance Enhanced Multiphoton Ionization (FIRE-MPI) is presented, and employed to elucidate the electronic structure of several polyatomic molecules. The method was used to search specific regions of electronic energy space in molecules for known, and previously unknown, electronic eigenstates. A secondary technique, Correlated Harmonic FIRE-MPI was devised and extends the capabilities to enable searching by eigenstate parity, or symmetry. The general nature of the method, which relies on a fundamental property of matter in strong radiation fields, that of field-induced eigenstate shifting, is demonstrated.; The studies present evidence for many new strong-field phenomena including field-induced eigenstate broadening and electron rescattering in the tunnel ionization regime. This represents the first observation of these phenomena. Field-induced eigenstate broadening seems to be a general phenomena and may be key to understanding and explaining a wide range of existing strong-field experiments, including the emerging area of optimal control of chemical reactivity. Field-induced eigenstate broadening is paramount to artificially increasing the bandwidth of the nominally narrow bandwidth femtosecond excitation source.; The work represents the extension of strong-field studies to polyatomic molecules, but also presents several new phenomena and theories about the underlying nature of strong-field radiation-matter coupling. |
