Mode-Specific Autodetachment Dynamics Of An Excited Non-Valence Quadrupole-Bound State

The autodetachment dynamics of vibrational Feshbach resonances of the quadrupole-bound state (QBS) for the first time has been investigated in real time for the first excited state of the 4-cyanophenoxide (4-CP) anion. Individual vibrational resonances of the cryogenically cooled 4-CP QBS have been unambiguously identified, and their autodetachment rates state-specifically measured using the picosecond timeresolved pump-probe technique employing the photoelectron velocity-map imaging method. The autodetachment lifetime (t) is found to be strongly dependent on mode, giving t values of similar to 56, similar to 27, and =2.8 ps for the 12'1 (E-vib = 406 cm(-1)), 12('2) (E-vib = 806 cm(-1)), and 21('1) (E-vib = 220 cm-1) modes, respectively. The striking mode-specific behavior of the QBS lifetime has been invoked by the physical model in which the loosely bound electron falls off by the dynamic wobbling of the three-dimensional quadrupole moment ellipsoid associated with the corresponding vibrational motion in the autodetachment process.