ISSN:
1089-7690
Quelle:
AIP Digital Archive
Thema:
Physik
,
Chemie und Pharmazie
Notizen:
Rotationally resolved infrared photodissociation spectra of the degenerate asymmetric C–H stretch vibration (ν3) of the CH3+–Ne and CH3+–Ne2 ionic complexes have been recorded. The rotational structure and vibrational frequencies are consistent with π-bound cluster geometries, where the Ne ligands are attached to either side of the 2pz orbital of the central C atom of the methyl cation, leading to C3v and D3h symmetric structures for the dimer and trimer. The intermolecular bonds in the ground vibrational state are characterized by averaged separations of Rc.m.=2.30 Å in the dimer and 2.34 Å in the trimer. The origins of the ν3 band are blueshifted by 11.5 and 21.5 cm−1 compared to the monomer frequency, indicating that vibrational excitation is accompanied by a small and additive destabilization of the intermolecular bond. Ab initio calculations at the MP2/aug-cc-pVTZ# level confirm that the π-bound configurations correspond to the global minimum structures for both the dimer (De=958.5 cm−1, Re=2.1347 Å, θe=91.4°) and the trimer (De=745.4 cm−1, Re=2.2322 Å, θe=90°). The calculated intermolecular potential energy surface of the dimer is characteristic for a disk-and-ball complex and reveals significant angular-radial coupling, which accounts for the large discrepancy between the vibrationally averaged and calculated equilibrium intermolecular separations, Rc.m.−Re(approximate)0.17 Å. The comparison of the ionic CH3+–Rg dimers (Rg=He, Ne, Ar, Kr, Xe) with the isoelectronic CH3X molecules (X=H, F, Cl, Br, I) reveals that chemical bonding onsets with Rg=Ar and increases with the size of the Rg atom. © 2000 American Institute of Physics.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1063/1.480783
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