Schulz C P, Claas P, Stienkemeier F
Max-Born-Institut, Max-Born-Strasse 2a, D-12489 Berlin, Germany.
Phys Rev Lett. 2001 Oct 8;87(15):153401. doi: 10.1103/PhysRevLett.87.153401. Epub 2001 Sep 21.
Superfluid helium nanodroplets are doped with potassium atoms to form complexes with the alkali atom residing on the surface of the droplets. Dispersed laser-induced fluorescence spectra of such systems already revealed the formation of M()He ( M = Na,K) exciplexes upon electronic excitation [Reho et al., Faraday Discuss. 108, 161 (1997)]. By means of femtosecond pump-probe spectroscopy, this formation process now is followed in real time. We find K()He(n = 1) to be formed within 180 fs. Furthermore, the existence of exciplexes with n>1 is quantified suggesting that the first ring around the potassium atom contains four helium atoms.
