An Extension of the ¹Π-¹Σ System of CH⁺ an the Identification of the λ 3579 Interstellar Line.

The `ITh' system of CH+ has been excited in a hollow-cathode discharge through helium containing a trace of acetylene. In addition to the V" = 0 progression already known, the V" = t progression has been observed up to and including V' = 4 From the position of the R(O) line of the 3-1 band, the position of the R(O) line of the 30 band has been determined and has been shown to coincide with the hitherto unidentified interstellar line X 3579 It is also shown that the previously accepted value for the ionization potential of CH is probably incorrect