First observation of the Comet-Tail (A2Πi→X2

In the emission spectrum of the 12C17O+ isotopologue the Comet-Tail (A2Πi→X2Σ+) system has been observed and analysed for the first time. 1215 spectral transitions in the 16 950 to 22 000 cm−1 region, belonging to three A−X (1−0,1−1 and 1−2) bands, were recorded with the Fourier-transform spectrometer and measured with an accuracy of 0.01 cm−1. As a result of analysis, 15 molecular parameters of the A2Πi(v=1) and X2Σ+(v=0,1,2) levels were obtained. The ro-vibronic term values of the A2Πi(v=1) level were also determined. Moreover, a very weak A2Πi(v=1)∼X2Σ+(v=11) perturbation of a complex, spin-orbit, spin-electronic and L−uncoupling character was identified and worked out. A percentage 2Π character of the A2Πi(v=1) and X2Σ+(v=11) levels was considered in detail.