Band Spectrum and Structure of the Ch⁺ Molecule; Identification of Three Interstellar Lines

In a discharge through helium, to which a small trace of benzene vapour is added, a new band system of the type 1 Π – 1 Σ is found which is shown to be due to the CH + molecule. The R(0) lines of the 0–0, 1–0, and 2–0 bands of the new system agree exactly with the hitherto unidentified interstellar lines 4232.58, 3957.72, 3745.33 Å, thus proving that CH + is present in interstellar space. At the same time this observation of the band system in absorption shows that the lower state 1 Σ is the ground state of the CH + molecule. The new bands are closely analogous to the 1 II – 1 Σ + BH bands. The analysis of the bands leads to the following vibrational and rotational constants of CH + in its ground state: [Formula: see text], B e ″ = 14.1767, α e ″ = 0.4898 cm. −1 . The internuclear distance is r e ″ = 1.1310∙10 −8 cm. (for further molecular constants see Table V). From the vibrational levels of the upper 1 Π state the heat of dissociation of CH + can be obtained within fairly narrow limits: D 0 (CH + ) = 3.61 ± 0.22 e.v. From this value the ionization potential of CH is derived to be I(CH) = 11.13 ± 0.22 e.v. The bearing of this value on recent work on ionization and dissociation of polyatomic molecules by electron impacts is briefly discussed.