Ultrafast Imaging of the Jahn–Teller Topography in Carbon Tetrachloride

Abstract

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 1T2 4p-Rydberg states, which then distorts through spontaneous symmetry breaking that we identify to follow the t2 bending motion. Photoionization of these states to three cationic states 2T1, 2T2, and 2E reveals a shift in the center-of-mass of the photoelectron peaks associated with the 2Tn 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 CCl4 t2 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.