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MO: Molekülphysik
MO 10: Spectroscopy I: Ultra-short Time Spectroscopy
MO 10.3: Talk
Thursday, April 5, 2001, 16:15–16:30, H1058
Photoinduced Ultrafast Dynamics in Solvated Alkali Atoms — •Christiana Bobbert, C.P. Schulz, and I.V. Hertel — Max-Born-Institut, Max-Born-Str. 2a, D-12489 Berlin, Germany
To understand the basic chemical process of solvation, the properties of alkali metal valence electrons in a finite polar environment are of fundamental interest. Dynamics of excited Na(H2O)n and Na(NH3)n clusters are studied by pump-probe technique. The lifetimes of the first electronically excited state of these complexes decrease strongly with increasing cluster size. The time constant τ of the Na(NH3)n complexes drops from 1 ns for n=1 down to τ < 1 ps for n > 4 and remains constant at 120 fs for larger clusters. The lifetimes of Na(H2O)n clusters are up to 10 times shorter. To obtain the lifetimes of large Na(H2O)n clusters 23 fs laser pulses have been applied. These measurements reveal a lifetime for complexes n>6 similar to the lifetimes of excited electrons in liquid water, which is around 100 fs. As expected, the electronically excited states of deuterated clusters live longer than the undeuterated species of the same size. The effect is strongest for cluster sizes n < 4 and is more visible for ammonia. These results can be explained by a fast internal conversion of electronic excitation energy into internal vibrations of the solvent molecules.