J. Phys. Chem. A, 105 (36), 8269-8272, 2001.

Delocalizing Electrons in Water with Light

Dong Hee Son, Patanjali Kambhampati, Tak W. Kee, and Paul F. Barbara

Abstract: Exptl. information on the spatial extent of the putative p and conduction band states of the hydrated electron (eeq) has been obtained by monitoring and controlling the electron/hole spatial sepn. of a photogenerated eeq/hole pair using a femtosecond laser pulse sequence. Optical excitation of eeq with two photons is obsd. to dramatically alter its spatial distribution and geminate recombination yield with the hole. One-photon excitation, in contrast, has no effect on the spatial distribution. The results strongly confirm theor. predictions on the size and location of excited states of eeq.


Figure 2. Time evolution of the hydrated electron concentration with (red lines) and without (blue lines) control pulse excitation using of 266 (a) and 400 nm (b-d) ionization pulses. The observed geminate recombination dynamics (red lines in a and b) are consistent with those of an earlier work. An analysis of these latter data in terms of the standard classical diffusion/geminate recombination model leads to estimates for lm of 8 and 14 Å with 266 and 400 nm ionization pulse, respectively. The blue lines correspond to three-pulse experiments with 800 nm control pulses arriving at 20 (a, b, and d) and 94 ps (c) after the ionization pulse. The DOD data in Figure 2d are the difference between the OD signal with the control pulse on and off for alternating pulses. The experiments were performed with an amplified Ti:sapphire laser system producing 35 fs pulses. The fundamental output from the amplifier at 800 nm was either doubled or tripled to produce the 400 or 266 nm photoionization pulses, whereas a portion of the fundamental was used as the control pulse. The remainder of the fundamental was used to generate the probe pulse at 650 nm which was derived from wavelength selected white light continuum. The instrument response was 50 fs (fwhm). The spot sizes/pulse energies at the sample were 100 mm/30 mJ (400 nm) and 5 mJ (266 nm), 300 mm/<1 nJ for the ionization, control, and probe pulse, respectively.