Search for dimer emission from photoexcited Al{sub 4}{sup -}

Aluminum cluster anions were stored in an electrostatic ion storage ring and irradiated by a laser pulse. Neutral as well as charged decay products emitted 20 {mu}s after the excitation were identified and recorded using the daughter ion mass spectrometry method. Besides delayed electron detachment, only monomer emission was observed for Al{sub 4}{sup -}. The branching ratio for the monomer channel was determined to be 8{+-}2%, while the dimer channel was found to be <0.01%.