Frequency and intensity analyses of the far infrared ν _5 band system of cyanogen (C _2N _2) and applications to Titan

摘要

The far infrared spectrum of cyanogen has been studied at high resolution to improve the rotational analysis of the ν _5 band system around 234cm ~(-1). Present in the sample in natural abundances, both isotopologues N ~(13)CCN and ~(15)NCCN have also been studied. The weak ν _4-ν _5 difference band centered at 270cm ~(-1) has been studied for the first time. On the basis of a global rovibrational analysis limited to the ν _2, ν _4, and ν _5 modes, energy levels up to 2300cm ~(-1) have been considered to contribute to the overall spectrum intensity at room temperature leading to a new line list of 196,994 lines. The line intensity prediction has been used to correct previous line intensity measurements by taking into account line mixing. A new vibrational transition moment has been deduced and compared to new band intensity measurements obtained by low resolution studies which are also presented in this paper. The agreement between both approaches is very good and rules out the apparent disagreement between line intensity and band intensity measurements observed in the past. An intensity study of 15NCCN is also proposed here thanks to the availability of a pure sample. Those results open the way to the search for isotopologues of cyanogen in Titan's atmosphere.