Velocity Map Imaging of the Single Ionization of Molecular Iodine

Single ionization in molecules is a critical first step in many higher order process, however it remains poorly understood even in simple diatomic systems. Velocity map imaging of ion fragments produced from dissociation after single ionization provide access to the kinetic energy released (KER) during dissociation. In this thesis, I will present two experimental studies of the single ionization of diatomic iodine. In a long wavelength scan spanning 400-800 nm the single ionization of I2 is found to have a contribution from deeply bound 5s electrons. In the I + I+ dissociation channel, much of the measured KER is inconsistent with ionization from the X, A, and B states of I2+ implying ionization from deeper orbitals. A pump-probe Fourier transform technique shows X and A state modulation is only seen for low KER dissociation through the B state. A narrow wavelength scan of the single ionization of I2 around the 530 nm one-photon B state resonance shows a strong enhancement in the branching ratio for inner orbital ionization while a weaker peak for outer orbital ionization occurs at a slightly different wavelength. The branching ratio from double ionization as a function of wavelength closely matches the branching ratio of single ionization of deep orbitals, implying that excitation of molecular ions generally comes about through inner orbital ionization. Current molecular ionization theory suggests that the least bound outer electrons will play a significant role in the single ionization of molecules. These findings are inconsistent with such ionization theories