Pump-probe spectroscopy dynamics modes

The double proton transfer of [2,2 -Bipyridyl]-3,3 -diol is investigated by UV-visible pump-probe spectroscopy with 30 fs time resolution. We find characteristic wavepacket motions for both the concerted double proton transfer and the sequential proton transfer that occur in parallel. The coherent excitation of an optically inactive, antisymmetric bending vibration is observed demonstrating that the reactive process itself and not only the optical excitation drives the vibrational motions. We show by the absence of a deuterium isotope effect that the ESIPT dynamics is entirely determined by the skeletal modes and that it should not be described by tunneling of the proton. 

Figure 4. Scheme of multistate fs dynamics for NeNePo pump-probe spectroscopy of Agj/ Ag4/Ag4 with structures and energy intervals for the pump and probe steps (A). Simulated NeNePo-ZEKE signals for the 50 K initial condition ensemble (B) at the probe energy of 6.41 eV and a pulse duration of 50 fs (C). Normal modes responsible for relaxation leading to oscillatory behavior of the signal are also shown [49]. 

A theory for the ultrafast pump-probe spectroscopy of large polyatomic molecules in condensed phases was developed in the work [15]. A multimode Brownian oscillator model was used to account for high-frequency molecular vibrations and local intermolecular modes as well as collective solvent motions. A semiclassical picture was provided using the density matrix in Liouville space. Conditions for the observation of quantum beats, spectral diffusion, and solvation dynamics (dynamic Stokes shift) are specified. 

Pump-probe absorption experiments on the femtosecond time scale generally fall into two effective types, depending on the duration and spectral width of the pump pulse. If tlie pump spectrum is significantly narrower in width than the electronic absorption line shape, transient hole-burning spectroscopy [101. 102. 103. 104. 105. 106. 107. 108. 109. 110. 111. 112 and 113] can be perfomied. The second type of experiment, dynamic absorption spectroscopy [57, 114. 115. 116. 117. 118. 119. 120. 121 and 122], can be perfomied if the pump and probe pulses are short compared to tlie period of the vibrational modes that are coupled to the electronic transition. 

This operation correlates the ground and excited states on both surfaces. The two-level charge-induced interchange of the conformers can occur on a timescale of a few picoseconds, which is typical for the resonant photoionization process [35], The dynamics of such a process, 0)° -> 1)+1 and 1)° -> 0)+1, is monitored in real time by the change in the anchoring A-N stretch, equal to Av(Au-N) = 145, 165 (due to the appearance of the A-N stretch doublet), and by the disappearance of the vibrational mode -v(N-H - N) (see Table 3) using, e.g. time-resolved picosecond UV/IR pump-probe ionization depletion spectroscopy [35]. 

The ultrafast photodissociation dynamics of the Na3 C state was analyzed with time-resolved two-color TPI spectroscopy in the picosecond regime. The two excitation wavelengths required, independently tunable for the pump and the probe pulse, were generated by a home-built synchronization of two mode-locked titanium sapphire lasers. The deconvoluted real-time spectra can be well described by a single exponential decay with a time constant strongly... 

---