Rotationally resolved A (2)Pi <- X (2)Pi electronic absorption spectrum ofcyanotriacetylene cation in the gas phase

The origin band of the A (2)Pi<--X (2)Pi electronic transition of cyanotria cetylene cation has been detected in the gas phase. The ions were generated in a liquid-nitrogen cooled hollow cathode discharge incorporated in a mul tiple reflection cell. The technique of frequency modulation absorption spe ctroscopy is used to observe the band at Doppler-limited resolution. Analys is of the rotational structure yields accurate values of the rotational con stants in the two electronic states, confirming a linear geometry. Comparis on with astronomical measurements of diffuse interstellar bands is made. (C ) 2000 American Institute of Physics. [S0021-9606(00)00615-2].