Evidence of an isomeric pair in furan...HCl: Fourier transform infrared spectroscopy and ab initio calculations.
For the first time the coexistence of a sigma- and a pi-complex in the C(4)H(4)O:HCl system has been observed, in the same supersonic expansion of a molecular jet seeded with argon (or helium) or in a flow-cooled cell at 240 K. This is an exception to the third of the Legon-Miller rules which claims the sigma-structure to be the only one to exist. On the grounds of energetic considerations and band contour simulations, two observed bands at 2787.7 and 2795.5 cm(-1) of the nu(s) HCl stretching frequency are assigned to the two complexes, recorded as Fourier transform infrared spectra with a resolution between 0.2 and 0.5 cm(-1). Complementary calculations show that the use of the standard second-order Moller-Plesset perturbation theory may be erroneous for such a complex, due of the overestimation of the dispersion contribution with respect to the electrostatic term. It is finally established that only a balanced version of the second-order Moller-Plesset perturbation method, spin-component scaled-MP2, or a higher level of theory like a coupled-cluster approach, can provide a reliable energetic analysis for this complex.
Asselin
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Laboratoire Dynamique, Interactions et Reactivite, UMR 7075, Universite Pierre et Marie Curie-Paris 6, CNRS, Case 49, 4 Place Jussieu, 75252 Paris Cedex 05, France. assel@ccr.jussieu.fr
Madebène
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B
Soulard
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Reinhardt
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P
Alikhani
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ME