Of the combination bands B2~ --> A2II, (0, 3) and (0, 4), the rotational structure has been analysed. With the aid of these and of the B2F. --> X2Z and the A-~II--~ X2Z band lines the combination principle was tested. The rotational constants were calculated. Intensity relations in the combination bands are qualitatively in good agreement with the theory for a case between H u n d's coupling cases a and b.
Of this spectrum three systems are known. The relative position of the electronic levels belonging to them may be seen in figure . Of two of these systems the rotational structure has already been analysed, viz. of the first negative car-B ~ ~Z bongroup (B 2 ~ I+ X 2 E) the vibrational transitions (0, 0), (0, 1), (0, 2), (1,2), (1, 3), (1,4), (2, 4), (2, 5), (3, 5), (3, 6) and (4, 7), and of the comet tail bands (A 2 II -+ X 2 Z) the transitions (3, 0), (4, 0), (5, 0), (6, 0), (7, 0), (8, 0), (4, 1), (5, I), (6, 2) and
We have now investigated the rotational structure of the third system, the B a i d e t-Johnson combination bands (B2E -~ 2 F A2II), notably the vibrational transitions t (0, 3) and (0, 4). In the near future I hope Fig. I. Electronic levels of the molecule CO+.
to analyse a few more of these bands, but at first sight this seems to be rather difficult as they are overlapped by the comet tail bands, which are much stronger. The two bands 1)