Binding energies and structures of C Ar n s 1 – 5 , clusters n from first principles

q Ž. We report the minimum energy geometries, binding energies and vibrational spectra of the C Ar n s 1–5 , clusters n which were recently recorded in a time-of-flight mass spectrometer. The C q Ar cluster has a planar structure with two long 3 and one short C–Ar bonds while the C q Ar cluster forms a square of D symmetry with the carbon atom in the center. The 4 4 h observed drop in the incremental binding energy for the successive Ar atom addition from n s 2 to n s 3 and from n s 4 to n s 5 justifies the classification of the n s 2 and 4 as magic number clusters in the experimental mass spectrum. q 1998 Elsevier Science B.V. All rights reserved.