Electronic absorption spectrum of a nonlinear carbon chain: trans-C6H4+

Abstract

The ²B_g–X²A_u transition of a nonlinear carbon chain trans-C₆H₄⁺, and trans-C₆D₄⁺, has been observed in the gas phase. The spectra were detected in the 580 nm region by direct absorption with a cavity ringdown technique through a supersonic planar discharge. Though the rotational structure is not resolved, the band profiles were analyzed using a “total spectral fitting” procedure using ground-state constants calculated by the CASSCF and CASPT2 methods. The molecular constants in the upper state could thus be determined.