Solvent induced symmetry breaking and relaxation following charge transfer to solvent excitation of Na^- in tetrahydrofuran

Pulses of 30 fs are used to follow the dynamics of charge-transfer to solvent (CTTS) in Na^- dissolved in tetrahydrofuran (THF). The photobleach of this transition is demonstrated to be orientationally anisotropic, indicating that the CTTS band consists of a number of orthogonally oriented transitions. The pronounced anisotropy of the bleach demonstrates that interaction with the solvent orients the transition dipoles, presumably by breaking the spherical symmetry which characterizes the isotropically absorbing Na^-_(g). The duration of solvent induced symmetry breaking was measured, and it was shown to persist for more than a picosecond. Rapid changes both in absorption and its anisotropy, which were not reported earlier, are apparent throughout the visible and near-IR. These are interpreted to reflect the presence of a primary photoproduct-tentatively assigned as the CTTS excited state, which decays completely within 200 fs. Assignment of later intermediates, analyzing the source of absorption anisotropies, and understanding the role played by the solvent in molding the photoinduced dynamics of sodide in THF are discussed.