Electronic absorption spectra of large benzene ⋅Arn clusters

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Abstract
We report the mass resolved resonant two‐photon ionizationspectra of C6D6⋅Ar n clusters up to n=70. Shifts of the benzene S 1←S 0 61 0 vibronic band were studied as a function of both cluster size and expansion conditions. We find that clusters in different size ranges exhibit remarkably different spectra, which also depend on expansion conditions and, hence, cluster internal energy. Below n=16, spectral features trend toward the blue with increasing size. Above n=16, all features exhibit weak size dependence over wide size ranges. In the n=20–40 range, four distinct bands were found, which we suggest could be due to fully enclosed fluxional (−55 cm−1 vs free C6D6), partially enclosed rigid (−43 cm−1), and one‐sided rigid (−32 cm−1) or one‐sided fluxional (also −32 cm−1, broader) structural types. Above n=40, only one band was definitely identified (at −26 cm−1), which may be due to a one‐sided rigid structural type. The trends in spectral shift vs size give no indication of approaching bulk‐like solvation of the benzene. Only one subpopulation between n=20 and 40 may show similarity to macroscopic benzene–argon solutions.