Infrared spectra of Cl~- - (C_2H_2)_n (1 <= n <= 9) anion clusters: Spectroscopic evidence for solvent shell closure

摘要

Mid-infrared vibrational predissociation spectra of mass selected Cl~- - (C_2H_2)_n (1 <= n <= 9) complexes have been recorded in the vicinity of the acetylene v_3 vibrational band (2700 - 3400 cm~(-1)). For clusters containing up to 6 acetylene ligands, the spectra each feature a single dominant band, shifted to lower frequency from the v_3 C-H stretch band of free acetylene, and are consistent with interior solvation structures, whereby roughly equivalent acetylene molecules are bound end-on to a central chloride anion. Spectra of the n = 7, 8, and 9 complexes, display multiple peaks and provide evidence for acetylene molecules situated in a second solvation shell and also for the existence of multiple isomeric forms. Depending on the cluster size, the inner solvation shell contains 6-8 acetylene molecules.