Trimer alkali

Small metal clusters have received considerable attention because of their possible involvement as "active sites" in a variety of catalyzed reactions. Although not particularly noted for their catalytic activity, alkali clusters have a simple chemical composition and may, therefore, model the more complicated systems in a manner analogous to the role played by the hydrogen atom in atomic structure. Less emphasized is the fundamental nature of alkali clusters per se. Since the ground state of Hj is not chemically bound, alkali trimers are the most elementary species which can exhibit a Jahn-Teller interaction. 

In previous electron spin resonance (ESR) studies of matrix isolated Naj (X, 1) and K3 3, 4), alkali trimers have been shown to be chemically bound and well described both by simple bonding ideas (1, 3) and by the more sophisticated calculations recently employed for Li3 (5), Na3 6) and Kj 7). For the potassium trimer in argon, two distinct ESR spectra are observed 3). An obtuse angled isomer corresponds to one of three static Jahn-Teller distortions from 03 symmetry, and is surprisingly similar to the... 

J. Higgins et at., Photo-induced chemical dynamics of high spin alkali trimers. Science 273, 629 (1996)... 

In the second part of this chapter (Sect. 3.2), different wave packet propagation phenomena in excited alkali trimers are discussed. The time-resolved pseudorotation of the sodium trimer is presented in Sect. 3.2.2. Last but not least, applying laser pulses of the same wavelength but of different pulse width enables a mode-selective preparation of the trimer, hence controlling its dynamics (Sect. 3.2.4). Wave packet propagation on a repulsive PES (Sect. 3.2.5), studied on the potassium trimer, leads to the phenomena of ultrafast photodissociation, which then is the topic of the subsequent chapter. 

Wave Packet Propagation Phenomena in Excited Alkali Trimers 101... 

Owing to their relatively simple electronic structure, the alkali trimers can be regarded as such model systems, to study, for example the principles of intramolecular vibrational redistribution (IVR) in photoexcited molecules or clusters. Among the alkali trimers Naa, especially when excited to its electronic B state, seems to be the best known. It acts in this section as a prototype for exploration of details of photoinduced IVR processes in real-time. Figure 3.35 sketches the principle of the experimental approach for triatomic s systems such as the Jahn-Teller distorted Naa B system. Compared to the investigations on the dimer systems, the only difference is that the energy surfaces involved get a dittle more complicated. 

A.J.C. Varandas and V.M.F. Morais, Semi-Empirical Valence Bond Potential Energy Surfaces for Homonuclear Alkali Trimers , Mol. Phys. 47, 1241 (1982). T.C. Thompson, G. Izmirlian Jr., S.J. Lemon, D.G. Truhlar, and C.A. Mead, Consistent Analytic Representation of the Two Lowest Potential Energy Surfaces for Lis, Nas, and Ks , J- Chem. Phys. 82, 5597 (1985). 

S. Rutz, H. Ruppe, E. Schreiber, and L. Woste, Femtosecond Wave Packet Dynamics in Alkali Trimers , Z. Phys. D 40, 25 (1997). 

J. Higgins, C. Callegari, J. Reho, F. Stienkemeier, W.E. Ernst, K.K. Lehmann, M. Gutowski, and G. Scoles, Photoinduced Chemical Dynamics of High-Spin Alkali Trimers , Science 273, 629 (1996). 

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