Rydberg states of cyanoacetylene investigated by (3 + 1) REMPI spectroscopy in the 77,000-90,000 cm−1 energy range

摘要

(3 + 1) resonantly enhanced multiphoton ionization (REMPI) spectroscopy coupled to photoelectron spectroscopy (REMPI-PES) has been carried out to study the Rydberg states of HC₃N in the 77,000-90,000 cm−1 region. Ab initio calculations (energies and optimized equilibrium geometries) have been performed for the first time for the low-lying 2Î , Ã2Σ+ and 2Î states of the cation HC₃N+ in order to help the analysis. Thanks to the combination of the three-photon REMPI spectra, one-photon spectrum and photoelectron spectra, unambiguous assignments of the Rydberg series and their vibrationally excited members are proposed. The electronic Rydberg structure of cyanoacetylene is very similar to that of C₂H₂ and HCN (almost identical quantum defects), fully supporting the present analysis. New three-photon allowed Rydberg series are identified belonging to ns and nd series. The three-photon vibrational band assignments, confirmed by the photoelectrons spectra, reveal excitation of only one or two quanta of the ν₂ (C ≡ N) mode. Apparent discrepancies between the three-photon REMPI spectrum and the one-photon absorption spectrum are removed via a minor re-assignment of the absorption spectrum previously analysed by Connors et al. J. Chem. Phys. 60(12), 5011 (1974). Finally the observed analogy with C₂H₂ and HCN can be rationalized by a partial relocalization of the 2π electrons upon excitation to Rydberg states converging to the 2Î state of HC₃N+, as predicted by the present ab initio calculations on the cation core.View full textDownload full textKeywordscyanoacetylene, propynenitrile, propiolonitrile, cyanoethyne, HC3N, Rydberg states, cationic states, π electron delocalization, REMPI spectroscopy, REMPI-PES, ab initio calculations of HC3N+ , cyanopolyyneRelated var addthis_config = { ui_cobrand: "Taylor & Francis Online", services_compact: "citeulike,netvibes,twitter,technorati,delicious,linkedin,facebook,stumbleupon,digg,google,more", pubid: "ra-4dff56cd6bb1830b" }; Add to shortlist Link Permalink http://dx.doi.org/10.1080/00268976.2012.706327