title: Formation of K*He exciplexes on the surface of helium nanodroplets studied in real time.
abstract: 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.
authors.affiliation: Max-Born-Institut, Max-Born-Strasse 2a, D-12489 Berlin, Germany.
authors.forename: C P
authors.initials: CP
authors.lastname: Schulz
authors.forename: P
authors.initials: P
authors.lastname: Claas
authors.forename: F
authors.initials: F
authors.lastname: Stienkemeier