Perylene-rare-gas heteroclusters. I. Electronic spectroscopy

In this paper we report on the electronic two-photon two-color near threshold spectroscopy of mass-resolved perylene-Ar_n (n=1-45), perylene-Kr_n (n=1-35), perylene·(N₂)_n (n=1-12), and perylene·(CH₄)_n (n=1-10) heteroclusters. The S₀→S₁ inhomogeneously broadened spectra of perylene·Ar_n (n=1-6) and perylene·Kr _n (n=1-4) exhibit resolved spectral features, which were assigned on the basis of experimental combination rules and polarizability relations to the electronic origins of distinct two-sided and one-sided structural isomers. Larger perylene·A_n (A=Ar, Kr; n=6-10) heteroclusters exhibit an "abnormal" specific size dependence of the red spectral shifts, which decrease with increasing n and reach a local minimum at n=8. Similar characteristics of the red spectral shifts are exhibited for perylene"(N₂)_n and perylene·(CH ₄)_n (n=4-8) heteroclusters. This abnormal size dependence of the spectral shifts is attributed to the dominance of one-sided single-layered and double-layered structural isomers in this cluster size domain. On the basis of the comparison between the spectroscopic data and molecular dynamics simulations of the absorption line shapes we have obtained a quantitative description of isomer-specific structures for n=2-6, a semiquantitative description of the abnormal size domain for n=6-10 (due to the dominance of one-sided structures with the abundance of two-layered structures increasing at higher n), the prevalence of one-sided structures for n=16 and n=22, and the realization of two-sided multilayered structures at n=45.