Absorption spectra of alkali metal anion CTTS transitions in liquid THF and DEE: sodide (dot-dashed curve) and potasside (solid curve) in DEE, taken from experimental data, and sodide (dotted curve) and potasside (thin dashed curve) in THF, taken from fit parameters given in the literature (Ref. 31). The sodide and potasside spectra in DEE were scaled to have the same maximum absorbance as reported in THF.
Spectra of the solvated electron and the neutral alkali product species created following CTTS excitation of alkali metal anions in DEE and THF: the (dotted curve) and (dot-dashed curve) tight-contact pairs in THF, taken from fit parameters given in the literature (Ref. 31); the spectra of these species in DEE have not been previously reported (Ref. 42). Also shown are the absorption spectra of the solvated electron in THF (dashed curve) and DEE (solid curve), reconstructed from spectral parameters given in the literature (Ref. 56).
Ultrafast spectral dynamics of the solvated electron ejected following both (upper panel) and (lower panel) CTTS excitations of in DEE. In both panels, the data are normalized at the maximum transient absorbance. The delayed rise and lack of solvation are consistent with the idea that DEE contains positively charged cavities, similar to what was observed previously for THF (Refs. 14 and 26).
Comparison of the ultrafast dynamics of the solvated electron ejected following the CTTS excitation of sodide in THF (solid curve) and sodide in DEE (dashed curve). The two traces are normalized at the maximum transient absorbance, showing that for in these two solvents the amount of short-time electron recombination is the same. We note that there are some differences in the longer-time recombination dynamics (not shown here), which have been reported previously in the literature (Ref. 16).
Comparison of the ultrafast dynamics of the solvated electron ejected following CTTS excitation of sodide in DEE at (dotted curve), sodide in THF at (dashed curve), and potasside in DEE at (thick solid curve). All three traces are normalized at the maximum transient absorbance. The instrumental cross correlation of the pump/ probe experiment is shown as the thin solid curve.
Schematic of our understanding of how the energies of the and ground and CTTS excited states (solid lines) lie relative to the solvent-supported disjoint states in DEE (gray-scale band with darker colors representing higher density of states). The ground state of is drawn higher in energy than the ground state of both because the electron affinity of K is lower than that of Na and because is less well solvated in DEE than (see text). The CTTS states of both and are depicted as consisting of three CTTS excited states whose positions can be separated in polarized hole-burning experiments (Refs. 13 and 16). Based on the similar recombination dynamics seen in Fig. 5, we have drawn the excitation of as accessing the same solvent disjoint states as the excitation of (arrows and dashed line).
Alkali atom D-line transient absorption dynamics following CTTS excitation of sodide at (left panel, probed at ) and potasside at (right panel, probed at ) in DEE. The strong transient absorption at early times is assigned to the weakly solvated, gas-phase-like neutral alkali atoms that solvate and eventually react to become alkali cation:solvated electron tight-contact pairs, whose spectra are shown in Fig. 2.
Calculated sizes of the alkali metal anions and neutral alkali cation:solvated electron tight-contact pairs in THF from spectral moment analysis using Eq. (4). The oscillator strengths were taken from the absorption spectra shown in Figs. 1 and 2 (Ref. 31). The size difference between and is the same as the size difference between and the , providing a reason why there are no qualitative differences in the decay of their D-line dynamics (Fig. 7).
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