화학공학소재연구정보센터
Journal of Physical Chemistry A, Vol.123, No.17, 3782-3792, 2019
Infrared Spectrum of Fulvenallene and Fulvenallenyl in Helium Droplets
Fulvenallene is the global minimum on the C7H6 potential energy surface. Rearrangement of fulvenallene to other C7H6 species and dissociation to produce fulvenallenyl radical (C7H5) is carried out in a continuous wave SiC pyrolysis furnace at 1500 K. Prompt pick-up and solvation by helium droplets allows for the acquisition of vibrational spectra of these species in the CH stretching region. Anharmonic frequencies for fulvenallene, fulvenallenyl, and three isomers of ethynylcyclopentadiene are computed ab initio; VPT2+K spectral simulations are based on hybrid CCSD(T) force fields with quadratic (cubic and quartic) force constants computed using the ANO1 (ANO0) basis set. The acetylenic CH stretch of the fulvenallenyl radical is a sensitive marker of the extent by which the unpaired electron is delocalized throughout the conjugated propargyl and cyclopentadienyl subunits. The nature of this electron delocalization is explored with spin density calculations at the ROHF-CCSD(T)/ANO1 level of theory. Atomic partitioning of the spin density allows for a description of the fulvenallenyl radical in terms of two resonance structures: fulvenallenyl is approximately 24% allenic and 76% acetylenic.