On the equilibrium structures of the complexes H2C3H+·Ar and c-C3H3+·Ar: Results of explicitly correlated coupled cluster calculations.

Explicitly correlated coupled cluster theory at the CCSD(T)-F12x (x = a, b) level [T. B. Adler et al., J. Chem. Phys. 127, 221106 (2007)] has been employed in a study of the potential energy surfaces for the complexes H2C3H+·Ar and c-C3H3+·Ar. For the former complex, a pronounced minimum with Cs symmetry was found (De ≈ 780 cm-1), well below the local 'H-bound' minimum with C2v symmetry (De ≈ 585 cm-1). The absorption at 3238 cm-1 found in the recent infrared photodissociation spectra [A. M. Ricks et al., J. Chem. Phys. 132, 051101 (2010)] is, thus, interpreted as an essentially free acetylenic CH stretching vibration of the propargyl cation. A global minimum of Cs symmetry was also obtained for c-C3H3+ (De ≈ 580 cm-1), but the energy difference with respect to the local C2v minimum is only 54 cm-1. [ABSTRACT FROM AUTHOR]