New spectroscopic studies of the comet- tail (A2Πi → X2Σ+) system of the 12C18O+ molecule

Four bands (with v' = 2-5 and common v'' = 0) of the comet-tail (A2Pii - > X2Sigma+) band system were recorded under high resolution by conventional, photographic spectroscopy and their modern analysis was carried out. The current investigations include a much greater region of the observed 12C18O+ molecule spectrum than before. In particular, the 5-0 band was recorded and studied for the first time. Thanks to the application of high resolution it was possible to record the complete set of 12 branches in all bands studied. The high precision of the measurements and the use of the commonly accepted theoretical model allowed us to obtain full spectroscopic characteristics of the analysed excited vibrational levels v' = 2-5 of the upper A2Pii state. In particular, the values of AD, p and q molecular constants for v' = 2, 3, 4 and all rotational parameters for v' = 5 were extracted for the first time. Also, the first values of the numerous equilibrium constants, as well as RKR parameters, were calculated. Finally, Franck-Condon factors and r-centroids for the comet-tail bands were provided.