Ionization propensity and electron momentum distribution of the toluene $S_1$ excited state studied by time-resolved binary $\left(e,2e\right)$ spectroscopy

We report a time-resolved electron momentum spectroscopy (TREMS) study on the toluene molecule in its $S_1$ excited state. The toluene $S_1$ state was prepared by a 267-nm pump laser and probed with a train of 1.2-keV incident electron beam pulses, each having 1-ps temporal width. It is shown through comparisons with molecular calculations that TREMS has an inherent capability to observe spatial distributions, in momentum space, of not only the outermost orbital but also all other, more tightly bound orbitals of a molecular excited state.

Figure 1

Comparisons of binding energy spectra between the experiments and SACCI calculations for the (a) $S_0$ and (b) $S_1$ states. The dashed lines show the contribution of each transition and the solid line is their sum. Vertical bars represent pole strengths $(>0.05)$.

Figure 2

EMS ionization schemes for transitions from the toluene $S_1$ state to several ionic states within the frozen orbital approximation, showing their occupation with electrons (closed circles) or holes (open circles).

Figure 3

Comparison of spherically averaged valence electron momentum distribution of the toluene $S_1$ state with that of the $S_0$ state as well as with the associated SACCI calculations.