Excess electrons facilitate redox reactions at the technologically relevant anatase TiO 2 (101) surface. The availability of these electrons is related to the defect concentration at the surface. We present two-photon (2PPE, 3.10-3.54 eV) and ultraviolet (UPS, 21.2 & 40.8 eV) photoemission spectroscopy measurements evidencing an increased concentration of excess electrons following electron bombardment at room temperature. Irradiationinduced surface oxygen vacancies are known to migrate into the sub-surface at this temperature, quickly equilibrating the surface defect concentration. Hence, we propose that the irradiated surface is hydroxylated. Peaks in UPS difference spectra are observed centred 8.45, 6.50 and 0.73 eV below the Fermi level, which are associated with the 3r and 1p hydroxyl molecular orbitals and Ti 3d band gap states, respectively. The higher concentration of excess electrons at the hydroxylated anatase (101) surface may increase the potential for redox reactions.

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The Stark spectra of autoionizing Rydberg states of Ar converging to the second ionization limit 3p5 2P1/2 have been investigated, experimentally and theoretically, as a function of electric field strength, in the range 15-2000 V cm-1. The levels with effective principal quantum number v=12-19, are excited by single-photon absorption from the ground state using a coherent extreme ultraviolet laser source (bandwidth approximately 1.0 cm-1) generated by four-wave sum-frequency mixing of the outputs of two pulsed dye lasers; a detailed Stark map is obtained for the first time. A multichannel quantum-defect-theory analysis of the field-induced-state mixing is carried out, reproducing positions, widths and shapes of the experimentally observed features. In addition, this analysis provides new insight into the dynamical decay of the autoionizing states.

Significant advances in laser technology have led to an increasing interest in the time evolution of Rydberg wavepackets as a means to understanding, and ultimately controlling, quantum phenomena. Rydberg wavepackets in molecules are particularly interesting as they possess many of the dynamical complications of large molecules, such as nonadiabatic coupling between the various degrees of freedom, yet they remain tractable experimentally and theoretically. This review explains in detail how the method of interfering wavepackets can be applied to observe and control Rydberg wavepackets in molecules; it discusses the achievements to date and the possibilities for the future.

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