Two-photon threshold ionization spectroscopy of perylene and van der waals complexes

Ionization thresholds have been determined for perylene and some of its van der Waals complexes. The Ar1 complexes have an ionization energy 46 cm−1 lower than bare perylene. This number compares favorably with recent data for tetracene, but is 4–6 times smaller than values obtained for argon complexes of single-ring aromatics. The (CH4)1 complex of perylene shows a rather similar shift to the argon case, 52 cm−1, the n-pentane complex has a red-shift of 10 cm−1 and the n-octane complex exhibits a blue-shift of 23 cm−1 (all values ±4 cm−1). In contrast, benzene/perylene has a large ionization red-shift of 700 cm−1. These data, together with results for larger clusters of Ar and CH4, indicate a strong dependence of the ionization energy shift on the spatial distribution of the adduct species with respect to the perylene substrate. With the possible exception of benzene complexation, the δI values are much smaller than might have been expected on the basis of previous work.