A supersonic cluster beam containing isomers of Al(C6H6) complexes was generated by laser evaporation, and non-destructively selected using a 2 m long electrostatic hexapole. The focusing curve shows clear evidence that there are two kinds of Al(C6H6) isomers which are slightly different from each other in geometry; one is an asymmetric 1,2-complex and the other nearly C6v symmetric 1,4-complex. The electric dipole moments of the two isomers are found to be 1.5 ± 0.1 and 1.4 ± 0.1 D, respectively. We carried out computation using density functional theory in order to estimate their structures. We found that the 1,2-complex is more stable than the 1,4-complex. The present work confirms that the electrostatic hexapole technique is useful for non-destructive selection of geometrical isomers in a beam.
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