This thesis explores the early-time electronic relaxation in sodium iodide aqueous solution exposed to a femtosecond ultra-violet laser pulse. Rather than initiating the charge transfer reaction by resonant one-photon photoexcitation of iodide, in the present time-resolved photoelectron spectroscopy study the charge-transfer-to-solvent (CTTS) states are populated via electronic excitation above the vacuum level. This is accomplished via a two-photon process using 266 nm (4.65 eV) laser pulses with a pulse duration of 60 fs. By analyzing the temporal evolution of electron yields from ionization of two transient species, assigned to CTTS and its first excited state, both their ultrafast population and relaxation dynamics were determined. For ionization a femtosecond laser probe photon of 3.55 eV photon energy is used. Comparison with resonant one-photon excitation studies shows that the highly excited initial states populated in the present wotk exhibit similar relaxation characteristics. Implications for structure and dynamical response of the solvation cage are discussed.
The measurements were conducted using a newly constructed experimental setup and time-of-flight electron spectrometer of the magnetic bottle type. The spectrometer was designed to measure the energy spectra of electrons generated from liquids excited by a strong laser field as well as by photons in the range from ultra-violet to soft X-rays. Its energy resolution ΔE/E is approximately 0.016 at kinetic energies of 100 eV. The collection efficiency of the spectrometer is determined for different kinetic energies, and the values are discussed for the magnetic-bottle configuration and the field-free arrangement.
Implementation of the recycle microjet technique offers uninterupted measurement condition over several hours, which is advantageous for time-resolved studies on diluted systems, and the possibility of recycling expensive or rare sample.