Towards a first-principles model of Fermi resonance in the alkyl CH stretch region: application to 1,2-diphenylethane and 2,2,2-paracyclophane.

摘要: The spectroscopy of two flexible hydrocarbons, 1,2-diphenylethane (DPE) and 2,2,2-paracyclophane (TCP) is presented, a predictive theoretical model for describing the alkyl CH stretch region these hydrocarbons developed. Ultraviolet hole-burning identified isomers DPE single conformation TCP present in supersonic jet expansion. Through analysis ground state low-frequency vibronic obtained by dispersed fluorescence, conformational assignments were made both TCP. found to retain low energy structures butane, being gauche anti structures. forms C 2 symmetric structure, differing from predicted lower 3 symmetry ethano bridges (−CH2CH2−) linking phenyl substituents. Resonant ion-dip infrared used record single-conformation IR spectra conformers conformer mid-IR that covers bend fundamentals. A local mode Hamiltonian incorporates cubic stretch-bend coupling Its parameters are density functional theory methods. Full dimensional calculations compared those use reduced Hamiltonians which anharmonic stretches scissor modes Fermi coupled. Excellent agreement found. Scale factors select terms determined fitting anti-DPE spectrum. scaled then predict successfully remaining experimentally region.