Xavier Bacalla, Edcel J. Salumbides, Harold Linnartz, Wim Ubachs, Dongfeng Zhao
Electronic spectra of C6H are measured in the 18 950-21 100 cm-1 domain using cavity ring-down spectroscopy of a supersonically expanding hydrocarbon plasma. In total, 19 (sub)bands of C6H are presented, all probing the vibrational manifold of the B2π electronically excited state. The assignments are guided by electronic spectra available from matrix isolation work, isotopic substitution experiments (yielding also spectra for 13C6H and C6D), predictions from ab initio calculations, and rotational fitting and vibrational contour simulations using the available ground state parameters as obtained from microwave experiments. Besides the 000 origin band, three nondegenerate stretching vibrations along the linear backbone of the C6H molecule are assigned: the ν6 mode associated with the C-C bond vibration and the ν4 and ν3 modes associated with C≡C triple bonds. For the two lowest ν11 and ν10 bending modes, a Renner-Teller analysis is performed identifying the μ2σ(ν11) and both μ2σ(ν10) and κ2σ(ν10) components. In addition, two higher lying bending modes are observed, which are tentatively assigned as μ2σ(ν9) and μ2σ(ν8) levels. In the excitation region below the first nondegenerate vibration (ν6), some 2π-2π transitions are observed that are assigned as even combination modes of low-lying bending vibrations. The same holds for a 2π 2π transition found above the ν6 level. From these spectroscopic data and the vibronic analysis a comprehensive energy level diagram for the B2π state of C6H is derived and presented. © 2016 American Chemical Society.
Department of Physics and Astronomy, LaserLaB, Vrije Universiteit Amsterdam, De Boelelaan 1081, Amsterdam, NL-1081 HV, Netherlands; Sackler Laboratory for Astrophysics, Leiden Observatory, Leiden University, P.O. Box 9513, Leiden, NL-2300 RA, Netherlands; Department of Physics, University of San Carlos, Nasipit, Talamban, Cebu City, 6000, Philippines; Hefei National Laboratory for Physical Sciences at the Microscale, Department of Chemical Physics, University of Science and Technology of China, 96 Jinzhai Road, Hefei, Anhui, 230026, China
