The first negative ( B2Σ +- X2Σ +) system of 13C 18O

The first negative ( B 2Σ +- X 2Σ +) system of the molecular ion 13C 18O + excited in the cathode glow of a hollow-cathode discharge tube was recorded in the spectral region 2110–2755 Å. Of the 22 bands observed with v′ = 0 to 4, and v″ = 0 to 7, the rotational structure of 13 bands was analyzed. The spin splitting of the spectral lines, which is a characteristic of a 2Σ +- 2Σ + transition, was observed in several bands. The molecular constants obtained from the analysis of the individual bands of this system were first merged together by the method of correlated least-squares fit. The resulting constants were then merged with those obtained from our recent studies of the comettail ( A 2Π i - X 2Σ +) system [C. V. V. Prasad and S. P. Reddy, J. Chem. Phys., 90, 3010 (1989)] and the Baldet-Johnson ( B 2Σ +- A 2Π i) system [S. P. Reddy and C. V. V. Prasad, J. Chem. Phys., 91, 1972 (1989)] of 13C 18O +, and a precise set of molecular constants for the X, A, and B states was obtained. Some of the derived constants of 13C 18O + in cm −1 are X 2 Σ + A 2 Π i B 2 Σ + B e 1.79468(2) 1.44258(2) 1.63374(2) α e 0.016440(3) 0.016791(4) 0.026003(7) ω e 2110.039(4) 1488.940(4) 1650.665(4) ω ex e 13.738(2) 12.411(2) 23.983(1) ω ey e −0.0032(2) 0.0228(2) - The astrophysical importance of this work is also briefly discussed.