Vibrational wavepacket dynamics

Matsumoto, Y., Watanabe, K. and Takagi, N. (2005) Excitation mechanism and ultrafast vibrational wavepacket dynamics of alkali-metal atoms on Pt(lll). Surf. Sci., 593, 110-115. 

Besides the electronic degrees of freedom several vibrational modes contribute and the essential features of the dynamics can only be understood by a multidimensional model. The multidimensional character causes an irreversible course of the ESIPT even though the transfer itself takes only 50 fs and vibrational dephasing occurs on a picosecond time scale. Nevertheless, most of the energetically accessible vibrations do not play a significant role and a realistic description of the ESIPT has to consider only a restricted number of vibrational degrees of freedom. As discussed in Ref [22] we think that these are general features for many ultrafast molecular processes. The observation of vibrational wavepacket dynamics in a number of systems [6, 75, 76], which exhibit other ultrafast processes, supports this conclusion. 

In conclusion, photoelectron angular distributions not only provide insightful fingerprints of vibrational wavepacket dynamics, but their strong... 

We use the transformation matrix U R) to represent the potential energy matrix, dipole moment matrix, and photoionization amplitudes in the diabatic representation. Then the vibrational wavefunctions are computed in the diabatic representation, but can also be transformed with U R) when we wish to see the adiabatic functions. The vibrational wavepacket dynamics and time-resolved photoelectron spectroscopy of the system is treated in Sec. 5.4. 

Fig. 5.15 Scheme to observe vibrational wavepacket dynamics through the conical intersection in NO2 (lower panel). Upper panel shows expected photoelectron energies from the four photoionization channels. (Reprinted with permission from Y. Arasaki et al., J. Chem. Phys. 132, 124307 (2010)). 

Knopp G, Pinkas I and Prior Y 2000 Two-dimensional time-delayed coherent anti-Stokes Raman spectroscopy and wavepacket dynamics of high ground-state vibrations J. Raman Spectrosc. 31 51... 

Long progressions of feature states in the two Franck-Condon active vibrational modes (CC stretch and /rani-bend) contain information about wavepacket dynamics in a two dimensional configuration space. Each feature state actually corresponds to a polyad, which is specified by three approximately conserved vibrational quantum numbers (the polyad quantum numbers nslretch, "resonance, and /total, [ r, res,fl)> and every symmetry accessible polyad is initially illuminated by exactly one a priori known Franck-Condon bright state. 

Heller [1. 2. 3] introduced and popularised wavepacket dynamics in the context of the theory of nioleculm iihotodissociation. In a photodissociation process, the molecule starts in a. well defined initial state and ends up in a firiiil scattering state. The initial bound state vibrational-rotatioiuil wavefunction provides a natural initial wavepacket in this case. 

Since the development of ultrashort lasers, nudear wavepacket dynamics of various matters have attracted continuing attention [1,2]. The research targets extend from gas phase molecules [3, 4] to molecules in solution [5, 6], and solids [7]. In general, an excitation of matter by an ultrashort pulse with sufficient bandwidth leads to the creation of coherence between vibrational (or vibronic) eigenstates [1]. The induced nuclear wavepacket then starts to evolve on a certain potential energy surface and the dynamics is probed by a suitable pump-probe spectroscopy. The direct time-domain observation of the nudear motion provides us with valuable information on photochemical reaction dynamics, vibrational excitation/relaxation mechanisms, electron-vibration (phonon) coupling, and so on. 

Nevertheless, detailed information on nudear wavepacket dynamics of surface adsorbates is important both from fundamental and from practical points of view. As is evidenced from the huge success of catalysis, solid surfaces sustain various kinds of reactions [8]. In order to understand the elementary steps of these reactions, the electronic and vibrational dynamics of surface adsorbates should be investigated in depth. Photochemistry at surfaces involves the photoinduced nuclear dynamics of adsorbates, which needs to be elucidated by ultrafast spectroscopy. Furthermore, combining with recently developed pulse shaping technologies [9], elucidation of the wavepacket dynamics will open up a novel laser control scheme of surface photochemical reactions. 

In this chapter we have surveyed recent experimental progress on the investigation of ultrafast nuclear wavepacket dynamics at surfaces. Nuclear (or vibrational) wavepackets of adsorbates are excited with ultrashort laser pulses, and subsequently their evolutions are probed with surface nonlinear spectroscopy such as 2PPE and SHG. These studies provide rich information on the initial stages of photoinduced... 

The initial dynamics of hydrogen transfer on this potential energy surface are determined by the propagation of the vibrational wavepacket created upon electronic excitation. 

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