Ultrafast Imaging of the Jahn-Teller Topography in Carbon Tetrachloride.

We report the direct time-domain observation of ultrafast dynamics driven by the Jahn-Teller effect. Using time-resolved photoelectron spectroscopy with a vacuum-ultraviolet femtosecond source to prepare high-lying Rydberg states of carbon tetrachloride, our measurements reveal the local topography of a Jahn-Teller conical intersection. The pump pulse prepares a configurationally mixed superposition of the degenerate 1 T 2 4p-Rydberg states, which then distorts through spontaneous symmetry breaking that we identify to follow the t 2 bending motion. Photoionization of these states to three cationic states 2 T 1 , 2 T 2 , and 2 E reveals a shift in the center-of-mass of the photoelectron peaks associated with the 2 T n states which reveals the local topography of the Jahn-Teller conical intersection region prepared by the pump pulse. Time-dependent density functional theory calculations confirm that the dominant nuclear motion observed in the spectrum is the CCl 4 t 2 bending mode. The large density of states in the VUV spectral region at 9.33 eV of carbon tetrachloride and strong vibronic coupling result in ultrafast decay of the excited-state signal with a time constant of 75(4) fs.