title: Vibrational spectroscopic study of vinyl substituted polycyclic aromatic hydrocarbons.
abstract: The mid infrared emission features observed in various astrophysical sources are attributed to polycyclic aromatic hydrocarbon (PAH) molecules. The models of emission spectra from a collection of PAHs show uncertainty in matching the 6.2 μm feature. This indicates the need to consider a larger variety of PAHs and PAH derivatives. Chemical pathways towards formation of PAHs in the astrophysical environments involve vinyl substituted PAHs as intermediate products. Vibrational spectroscopic study of vinyl-PAHs is reported in the present work. The vinyl group is substituted at similar positions in eight different PAHs. The obtained optimized structures show that vinyl substitution at 2 position in acenes gives planar geometry, while all other vinyl-PAHs are non-planar. Infrared spectra is simulated for neutrals as well as for cations. The results are compared with the spectra of corresponding plain PAHs and analyzed for possible match with astrophysical observations. New features, due to vinyl group in the composite spectra, identified at 6.64, 6.92, 7.27, 8.77 and 10.35 μm fall close to some sub features of the observed emission spectra. The paper provides data that may be used in the emission models particularly along proto planetary nebulae type cool objects.
authors.affiliation: Department of Physics, D.D.U. Gorakhpur University, Gorakhpur 273009, India.
authors.forename: Anju
authors.initials: A
authors.lastname: Maurya
authors.affiliation: Department of Physics, D.D.U. Gorakhpur University, Gorakhpur 273009, India. Electronic address: shantanu_r@hotmail.com.
authors.forename: Shantanu
authors.initials: S
authors.lastname: Rastogi
keywords: Aromatic infrared bands; Astrochemistry; DFT calculations; Interstellar molecules; PAH