ULTRAFAST FRAGMENTATION OF SMALL ALKALI ATOM-AMMONIA CLUSTERS

Ultrafast dynamics of small, free alkali atom-ammonia clusters Na(NH3) (n) studied using amplified 150 fs Ti:sapphire laser radiation (red: 7 70-820 nm). Pump-probe experiments using the red photon to excite and the second harmonics (blue: 385-410 nm) to ionize the clusters show th at the first electronically excited state of NaNH3(($) over bar A(2)E) is Stable for times tau > 1 ns. Larger cluster ions can only be obser ved for short delay times, indicating life times of the excited states of typically tau similar to 30 Ps for Na(NH3)(2). In addition, a sign ificant Na+ ion signal rises on the same time scale, indicating fragme ntation of the clusters and demonstrating a genuine 'pump-control' exp eriment.