Spectroscopic signatures of structural aufbau in (benzene)n; n=7–19

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Abstract
Optical spectra of larger (benzene)n clusters, n=7–19, have been investigated in detail using the molecular B2u←A1g000 and 610 transitions. The clusters are formed in a helium jet and are detected mass selectively by two‐color resonant two‐photon ionization spectroscopy at moderate resolution. The association of spectral line shifts with distinct molecular sites leads to a simple picture of the building up of clusters of nonpolar molecules, as proposed earlier [Easter et al. Chem. Phys. Lett. 1 5 7, 277 (1989)]. Coarse band shapes and fingerprintlike fine structure are discussed in terms of the numbers and multiplicities of sites predicted by the icosahedral aufbau sequence, and yield a particularly clear correspondence around B13, whose quasiicosahedral structure (as determined by minimum‐energy simulations) forms the sequence’s core. Distinctive multiplet structure observed in the center of the 610 band for n=12–15 is attributed to exciton interactions among equivalent sites.