ISOMERIC STRUCTURES, VAN-DER-WAALS FREQUENCIES AND SPECTRAL SHIFTS OFCOLD 4-FLUOROSTYRENE-(ARGON)(N) CLUSTERS (N = 1 TO 4)

New spectroscopic results on 4-fluorostyrene (4FSTY) solvated by n arg on atoms (n = 1 to 4) have been obtained by resonant two-photon ioniza tion. The spectral features associated with the 4FSTY-Ar cluster have been understood in relation with a fully quantum calculation of the ro vibrational states, and those associated with clusters n = 2 to 4 than ks to a classical calculation allowing to find stable isomeric structu res. Different isomers have been characterized from their spectral sig natures: as was previously shown for aniline-Ar(n) van der Waals clust ers [P. Hermine, P. Parneix, B. Coutant, F.G. Amar and Ph. Brechignac, Z. Physik D 22 (1999) 529], net isomer specific electronic shifts tow ards the blue have been observed, which reveal in this case the non eq uivalence of the binding sites that argon atoms can occupy near the vy nilic group substituent.