Motions in Excited State Hydrogen Transfer

Low-frequency Motions in Excited State Hydrogen Transfer 

A similar study with substantially improved time resolution has been reported recently [8, 37, 38]. In such experiments, HBT was excited to the enol-Sj state by a 40 fs pulse at 350 nm, i.e., nearly resonant to the Sq-Sj transition. Transient vibrational spectra were measured with 100 fs mid-infrared probe pulses which were spectrally dispersed after interaction with the sample. Such spectra are displayed in Fig. 15.8 (b) for different delay times, together with the stationary vibrational spectrum in the enol ground state of HBT [Fig. 15.8 (c)j. In agreement with Ref [7], the spectra display a prominent new band around 1530 cm i with a spectral 

The carbonyl stretching and other fingerprint bands of keto H BT show only minor changes of their spectral envelope and the spectrally integrated absorption as a function of time. In particular, contributions from the v = 1 2 transition of 

Such excess energy is mainly contained in low-frequency modes of the keto species, as has been discussed in detail in Ref [8], 

Excitation of the enol species to the Sj state induces a redistribution of electronic charge. For a strong electronic coupling between the initially excited vibronic states and the keto excited state, this charge redistribution occurs on a time scale much faster than 20 fs and establishes an excited state potential energy surface with a minimum for the keto-type configuration of the molecule. 

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