Figure 8.

Comparison of the measured vibrational echo data (black) with the calculated vibrational echo data (red) for the N_ε–H tautomer of His64. The vibrational echo signals were calculated using the FFCFs shown in Figure 6a. The parameters used in the vibrational echo calculation are listed in Table 2. Spectrally resolved vibrational echo decays are shown for the frequencies 1930, 1935, 1940, and 1945 cm⁻¹, and T_w = 0 ps (a–d), 2 ps (e–h), and 8 ps (i–l). Vibrational echo decays for a particular frequency as a function of T_w are in columns. The oscillations in the echo decays in panels c and d are due to anharmonic accidental degeneracy beats³⁸,⁷⁷,⁸¹ between the 0–1 transition of the A₁ line and the 1–2 transition of the A₀ line.