Dynamic Interplay\nbetween the Mode-Randomization and\nAutodetachment of the Dipole-Bound States of the Anion

State-specific dynamics of the dipole-bound state (DBS)\nof the\ncryogenically cooled deprotonated 4,4′-biphenol anion have\nbeen investigated by picosecond time-resolved pump–probe spectroscopy.\nFor DBS vibrational states below the electron-detachment threshold,\nthe relaxation rate is slow to give a lifetime (τ) longer than\n∼5 ns, and it is attributed to the nonvalence-to-valence orbital\ntransformation. For the DBS resonances above the detachment threshold,\nhowever, the lifetime decreases with the activation of autodetachment,\nwhereas the otherwise zeroth DBS modes seem to be randomized by intramolecular\nvibrational energy redistribution (IVR), as manifested in the biexponential\ntransients. As the DBS internal energy increases further, the lifetime\nshows a monotonic decrease to give τ ∼ 50 ps at <i>E</i>′<sub>vib</sub> ∼ 1700 cm<sup>–1</sup>. This study demonstrates that IVR may play an important role in\nthe autodetachment dynamics when the density of states rapidly increases\nwith increasing vibrational energy, giving important implications\nfor the electron-transfer dynamics taking place in large biological\nor astrochemical systems.