Λ-type Doublets and Lifetime Broadening in the B2Π-X2Π Electronic Origin Band of C6H
We present a high-resolution study on the B2Π-X2Π electronic origin band spectrum of the C6H radical with its cen-ter at～18990 cm-1.The C6H radicals are produced in a pulsed supersonic slit-jet discharge source and detected in direct absorption by sensitive cavity ring-down spectroscopy.By using a home-made narrow linewidth nanosecond pulsed laser source,the experimental spectrum allows to resolve the Λ-type doublet fine structures in high-J rotational lines.A set of improved B2Π state constants,including the Λ-type doubling parameters of p'=-1.16(9)x10-3 cm-1,q'=-1.22(7)x10-4 cm-1,are determined from analysis of the experimental spectrum.An analysis on the spectral line profile has result-ed in a significant linewidth broadening of～0.05±0.01 cm-1,corresponding to a B2Π state life-time of～100±20 ps.The short lifetime of the excited B2Π state is proposed due to fast inter-nal vibronic couplings to high-lying vibronic levels of lower electronic states.
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