Hole-Burning Spectra of Phenol-Ar_n(n = 1,2)Clusters:Resolution of the Isomer Issue

摘要

The hole-burning(HB)spectra of phenol-Ar_n(PhOH-Ar_n)clusters with n=1 and 2 have been measured in a molecular beam to clarify the possible existence of isomers.Two species were identified to give rise to signals in the S_1- S_0 spectrum recorded for the n = 1 cluster;however,one of the species was found to originate from dissociation of an n = 2 cluster.Similarly,three species were observed in the spectrum of the n = 2 cluster,and two of them were assigned to n = 3 and larger clusters.The spectral contamination from larger size clusters was quantitatively explained by the dissociation after photoexcitation.The analysis of the spectra demonstrates that only a single isomer exists in the molecular beam for both the n = 1 and the n = 2 clusters.In addition to two previously detected intermolecular modes,a third low-frequency mode,assigned to an intermolecular bending vibration,is observed for the first time in the HB spectrum of the n = 2 cluster.The assignments of the intermolecular vibrations were confirmed by ab initio MO calculations.The observation of the third intermolecular vibration suggests that the geometry of the n = 2 cluster has C_s or lower symmetry.