Rotationally resolved A~2#PI# implied by X~2#PI# electronic spectra of cyanodiacetylene and dicyanoacetylene cations

摘要

The 0_0~0 bands of the A ~2#PI# implied by X~2#PI# and A ~2#PI#_g implied by X~2#PI#_u transitions of cyanodiacetylene and dicyanoacetylene cations have been rotationally analyzed at Doppler-limited resolution using frequency modulation absorption spectroscopy. The ions were generated in a liquid-nitrogen cooled hollow cathode modulated discharge incorporated in a White cell. Analysis of the rotational structure yields molecular parameters of the cations in the two electronic states, confirming linear geometries. The inferred spin-orbit and rotational constants are discussed in terms of the electronic structure of the isoelectronic cations. The spectrum of dicyanoacetylene cation reveals #LAMBDA#-type doubling consistent with the presence of a nearby ~2#SIGMA#_g~+ state. The second order spin-orbit splitting of the A ~2#PI#_g state is analyzed to predict the existence of the ~2#SIGMA#_g~+ state below the A ~2#PI#_g state.