The Ar–C2H2 intermolecular potential from high resolution spectroscopy and ab initio theory: A case for multicenter interactions

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Abstract
Infrared spectra have been obtained for the Ar–C2H2 complex, which include a combination band associated with the low frequency bending mode. These data are used, together with ab initio calculations and the results of previous studies of this system, to construct a two‐dimensional Hartree–Fock plus damped dispersion (HFD) intermolecular potentialsurface corresponding to the C–H stretch excited vibrational state. A high quality SCF surface, which includes ghost orbital corrections, has been used to fix the repulsive part of the potential. The remaining potential parameters were initially estimated with the aid of various combining rules and the collocation technique was used to solve the bound state problem for this potential and to calculate the spectrum of the Ar–C2H2 complex. To obtain good agreement between the calculated and experimental spectra it was necessary to distribute the dispersion interaction over the length of the acetylene subunit. The result is a double minimum potential upon which the complex executes wide amplitude bending motion.

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