Novel geminate recombination channel after indirect photoionization of water
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(a) Transient spectra measured at various delay times after two-photon excitation (2 × 270 nm) of neat water. Experimental points, lines are drawn as a guide to the eye. (b) Integrated area under the transient spectra (arbitrary units) vs. the delay time. Comparison to the pump-probe transient measure at 700 nm (blue line) indicates an accelerated decay within the first 3 ps and gives evidence for an additional fast recombination channel. (c) Pump-probe transients measured after two-photon excitation of neat H2O and D2O at 270 nm. Similar data measured in and after excitation at 202 nm. Probe wavelength 700 nm, room temperature.
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(a) Absorption changes measured at 700 nm in H2O after 2 × 270 nm excitation (red curve) and with an additional repump pulse with fixed delay time t 12 = 1 ps after the UV pump (cyan). The difference Δ(ΔOD) of both signals represents the PREP signal shown in orange. (b) The pulse sequence and definition of delay times for the PREP measurements. [(c) and (e)] PREP data measured in H2O (red) and D2O (green) for fixed repump-probe delay times t 23 = 0.1 ps (c) and 150 ps (e). The corresponding signals measured after photodetachment of and at 6.1 eV are shown in black and blue, respectively. The data are measured at 700 nm and variable repump delay times t 12. [(d) and (f)] Magnification for shorter repump delay times from panel (e), plotted in arbitrary units for protonated (d) and deutereted samples (f). Experimental points, calculated solid lines.
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