Real-Time Observation of Fermi Resonances in the S₁ State of Phenol

Abstract

Fermi resonances in the first electronically excited (S1) state of phenol have been observed in real time. Quantum beats associated with coherent superposition of Fermi resonant eigenstates are manifested as temporal oscillations of the ionization cross sections of which the amplitudes are strongly dependent on the total ionization energy. This indicates that coherently excited eigenstates are effectively decomposed into their zeroth-order states, providing the unique opportunity for the investigation of nonstationary state dynamics in real-time. Energy gaps (Δν̃) of eigenstates within the laser coherence width have been most precisely determined up to date, giving Δν̃ ∼ 3.302 ± 0.001 or 1.655 ± 0.001 cm–1 for the 11/4110b1 or 122/8a1 Fermi doublets, respectively. Dephasing rate suddenly increases as the S1 internal energy becomes above ∼1500 cm–1, revealing the important role of energy randomization dynamics during the H atom tunneling process of phenol in S1.

Tunneling dynamics dictated by the multidimensional conical intersection seam in the πσ*‐mediated photochemistry of heteroaromatic molecules

“…It is quite notable that the prominent quantum beats have been observed for several Fermi‐doublets in the S 1 phenol 133 . For example, the Fermi‐doublet located at the S 1 internal energy of 935 and 938 cm −1 (Figure 2) represent a couple of eigenstates resulting from the Fermi‐type coupling of the optically bright 1 1 fundamental and optically dark 4 1 10b 1 combinational modes (Figure 3).…”