Rotationally resolved (A)over-tilde(2)Pi(g)<-(X)over-tilde(2)Pi(u) electronic spectrum of triacetylene cation by frequency modulation absorption spectroscopy

The spectrum of the (A)over-tilde(2)Pi(g) <-- (X)over-tilde(2)Pi(u) 0(0)(0) band system of the triacetylene cation and isotopic derivatives DC6H+ and C6D2+ have been studied at Doppler-limited resolution using frequency modul ation absorption spectroscopy. The ions were generated in a liquid-nitrogen -cooled hollow cathode discharge incorporated in a White cell. A discharge modulation in combination with the frequency modulation technique was used to enhance the detection sensitivity. Analyses of the rotational structure yield accurate rotational and spin-orbit interaction constants of triacetyl ene cation in the two electronic states and information on its geometry. (C ) 1999 American Institute of Physics. [S0021-9606(99)01501-9].