The experimental setup in front and side view. See details in the text.
Electron source images at the MCP for (a) gas phase experiments and (b) liquid jet experiments. The gray area is the active area of the phosphor screen behind the MCPs. The dashed circle around the signal indicates the image of the microskimmer orifice (in this case about diameter). For details see text.
A commercial Ti:sapphire laser generates sub-50 fs pulses at 800 nm. Nonlinear processes [harmonic generation or, alternatively, frequency generation in a collinear optical parametric amplifier of super-fluorescence (TOPAS)] are used to generate pump and probe pulses of the desired wavelength (in this case third and fourth harmonic generations).
Top: photoelectron spectra of NO obtained by multiphoton ionization with 4.65 and 6.2 eV photons. The bands are assigned to vibrational bands in the ion (Ref. 20). Bottom: the expected electron kinetic energy according to Eq. (1) is plotted against the TOF in the NO-spectrum. To extract the calibration parameters of our spectrometer, these points are fitted with Eq. (2). Note that the calibration holds only for the direct electron trajectories.
Photoelectron spectrum of NO obtained by 200 nm, two-photon ionization. The experimental data are well reproduced by the sum of vibrational bands in the NO ion, convolved with an instrument function as given in Eq. (3).
Concentration dependence of the 200 nm one-color TOF-spectrum, the 266 nm one-color TOF-spectrum, and the pump-probe TOF-spectrum (300 ps delay) of an aqueous NaI solution. Black: 500 mmol/l, blue: 100 mmol/l, green: 30 mmol/l, red: 10 mmol/l, magenta: 3 mmol/l. Spectra were smoothed by a FFT-filter and normalized. Vertical lines mark main contributions to the signal (solid: solvated electrons, dashed: water, dotted: iodide).
Time-resolved photoelectron spectrum of (a) 100 mM sodium iodide solution. Excitation of the iodide ion leads to formation of solvated electrons at a delay time of 0 ps and subsequent thermalization and decay processes. A global fit (lines) identifies two transients corresponding to ionization of initially hot and cold electrons with (b) distinct spectra and (c) distinct population dynamics. The contributions of hot and cold electrons to the total signal are shown in (d) and (e).
Kinetic energy dependent fit parameters for the apparatus function (3).
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