Resonance enhanced ionization scheme involving the potential energy surfaces of the 1,3-cyclohexadiene/1,3,5-hexatriene system. In the one-color two-photon ionization scheme, a laser pulse with photon energy populates first the state and then the ground state of the ion. Rapid energy transfer occurs from the state to the state upon excitation, of which the early parts bear signature in the photoelectron spectrum. In the two-color three-photon ionization scheme, a second photon of energy brings the molecules to a valence state, from which the Rydberg states are populated by internal conversion. A third laser photon ionizes the molecules.
The time-of-flight mass spectrum obtained upon resonance enhanced one-color two-photon ionization of CHD with femtosecond laser pulses at .
One-color two-photon ionization-photoelectron spectra obtained from ionization via the transient state, for laser wavelengths between 275 and , as indicated.
A comparison of the photoelectron spectrum (upper trace, dashed) with the Rydberg absorption spectrum (lower trace, solid line) obtained by Merchán et al. (Ref. 46) illustrating the similarity of the spectra. The photoelectron spectrum, taken at , is plotted against the scale at the top of the graph, while the absorption spectrum is plotted against the scale at the bottom. The absorption spectrum was digitized and reproduced with permission from Merchán et al. (Ref. 46).
(a) Peak widths vs laser wavelengths, resulting from the deconvolution of the photoelectron spectra. Plotted is the full width at half maximum of the Gaussian fits. (b) Peak intensities vs laser wavelengths.
The Rydberg spectrum of 1,3-cyclohexadiene obtained by exciting through the valence levels using a two-color three-photon ionization process and a one-color four-photon ionization process. The observed peaks are assigned by their principal quantum numbers and quantum defects. For the one-color spectrum the laser wavelength was , while for the two-color spectrum the laser wavelengths were 400 and .
The time-resolved decay dynamics of 1,3-CHD (solid dots) obtained by delaying the photon with respect to the photon. The instrument function, which was obtained using azulene, is plotted as hollow circles. The fits for the temporal profile of the CHD signal were obtained with a rise time of and a decay time of . The inset shows the logarithmic plot of the decay curve and the exponential fit for the latter part of the time delay.
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