Search for dimer emission from photoexcited ${{\mathbf{Al}}_4}^{-}$

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 $20\hspace{0.5em}\mathrm{\mu }\mathrm{s}$ after the excitation were identified and recorded using the daughter ion mass spectrometry method. Besides delayed electron detachment, only monomer emission was observed for ${{\mathrm{Al}}_4}^{-}$. The branching ratio for the monomer channel was determined to be $8\pm 2\%$, while the dimer channel was found to be $<0.01\%$.

Figure 1

Schematic of the electrostatic storage ELISA.

Figure 2

Position of the ${{\mathrm{Al}}_4}^{-}$ bunch and their decay products at various times relative to the time the laser was fired ($t_{\mathrm{laser}}$). The time steps are multiples of $T/4$ with $T$ being the revolution time of the ions in the ring. See main text for more details.

Figure 3

A fragment spectrum obtained with ${{\mathrm{Al}}_4}^{-}$ clusters about $20\hspace{0.5em}\mathrm{\mu }\mathrm{s}$ after absorption of a laser photon of 2.063 eV. The expected positions for ${{\mathrm{Al}}_2}^{-}$ and ${{\mathrm{Al}}_1}^{-}$ fragments are indicated by the dotted lines.

Figure 4

Measurement of the relative probability for delayed electron detachment and one-atom loss for laser excited ($E_{\lambda }=2.063\hspace{0.5em}\mathrm{eV}$) ${{\mathrm{Al}}_4}^{-}$. (Upper panel) Voltage setting of the storage ring as a function of time relative to the laser pulse. (Lower panel) Number of counts detected with the MCP as a function of time (see main text for more details).