(1 + 1′) REMPI spectrum via the S1 excited state in pFT obtained using 1 ps laser pulses with a pump-probe time delay of +10 ps and a fixed probe wavelength of 284.3 nm. Total photoelectron intensity is plotted versus S1 internal energy.
SEVI spectra for pFT measured at a pump-probe time delay of 0 ps via (a) S1 18a1 and (b) S1 origin. Each SEVI spectrum results from splicing together photoelectron spectra obtained using five different probe wavelengths. In (c), a nanosecond photoelectron spectrum measured via S1 18a1 is presented for comparison with the picosecond spectrum in (a).
Slow electron velocity-map imaging (SEVI) spectra measured via S1 18a1 in pFT at pump-probe time delays of (a) 0 ps, (b) 4 ps, (c) 8 ps, (d) 12 ps, (e) 100 ps, and (f) 500 ps. The area under each spectrum is normalized to a constant value and the intensity scale is the same for each plot. As the time delay increases, the intensity of the largest feature decreases and the spectra become more congested. In (b), the features labeled A to F indicate ion peaks for which the time-dependent intensity has been determined.
Plots of the time-dependence of the photoelectron peak intensity corresponding to D0 18a1 in pFT (peak A) over the ranges (a) 0 ps to 500 ps and (b) 0 ps to 20 ps. The filled circles represent experimental results, the x-axis error bars are ±0.25 ps, and the y-axis error bars are ±4%. The solid lines represent fits of the experimental intensities to equations given in Sec. III A.
Plots showing the time-dependent intensities corresponding to six different ion peaks observed in the photoelectron spectra measured via S1 18a1 in pFT. Plots (a) to (f) correspond to ion peaks labeled A to F in Fig. 3. The filled circles represent experimental data points, and the solid lines represent fits to equations given in Sec. III A. A different intensity scale is used for each plot so that changes in ion peak intensities with time are easily observed.
Simulations of the measured time-dependent intensities for (a) ion peak A, (b) ion peak B, and (c) ion peak C, for comparison with Figs. 5(a)–5(c), respectively.
Schematic diagram of the tier model structure used for analysis of the IVR dynamics following excitation of S1 18a1 in pFT. In the lower part of the figure, S1 vibrational states that satisfy the selection rules for coupling to S1 18a1 0a1 ′ and whose energies are calculated to be 845 ± 25 cm−1 are arranged in tiers, as described in the text. The state assigned to doorway state |b⟩ is indicated by the thick line in tier 1. In the upper part of the figure schematic illustrations of photoelectron spectra are shown for three time delays characteristic of ionization predominantly from (i) bright state |a⟩ (t = 0 ps), (ii) doorway state |b⟩ (t = 4 ps) and (iii) the bath states (t ≫ 17 ps).
Schematic diagrams of calculated vibrational modes in the S1 excited state of pFT assigned to (a) the in-plane ring bending mode ν18a and (b) the CH out-of-plane mode ν17a.
Parameters obtained from fits to the normalized time-dependent ion peak intensities S(t). The fit equation used for ion peaks A, E, and F is S(t) = Xexp ( − t/τ X ) + Ycos (2πt/τ osc )exp ( − t/τ Y ) + Z and the equation used for ion peaks B, C, and D is S(t) = X[1 − exp ( − t/τ X )] + Ycos (2πt/τ osc )exp ( − t/τ Y ) + Z.
Calculated and experimental vibrational frequencies for pFT in the ground state neutral (S0), the lowest excited state neutral (S1), and the ground ionic state, (D0). Values are given for 15 vibrational modes that have S1 fundamental frequencies lower than 845 cm−1.
Comparison of IVR lifetimes for various S1 vibrational states in pFT determined from experiments using picosecond photoelectron spectroscopy (ps-PES) for jet-cooled samples and a chemical timing technique for room temperature samples.
Zero-order energies of selected torsional levels in S1 and D0. These values are used to determine the torsion-vibration energies of dark states that could potentially couple to bright state components S1 18a1 0a1 ′ and S1 18a1 1e″.
Energies (cm−1) and assignments (vibrational and torsional) for the zero-order dark states predicted to lie in tiers 1 and 2 of the tier model structures (see text for details). These states fulfill the criteria for coupling to the bright state components (a) S1 18a1 0a1 ′ and (b) S1 18a1 1e′′.
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