Knowledge Bank

The $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}\Pi \to 1\Sigma$ band system of $CH+$ has been excited in a hollow cathode discharge through helium containing a trace of acetylene and has been photographed with a ten meter spectrograph. In addition to certain bands already known, the (3-1) band has been observed. From the wavelength of the R(0) line of this band and the known value of $\Delta G\prime (1/2)$, the wavelength of the R(0) line of the (3-0) band has been determined. Within the accuracy of the preliminary measurements the R(0) line of the (3-0) band of $CH+$ contains with the hitherto unidentified interstellar line at 3579.04 \AA. This agreement, together with the fact that the R (0) lines of the (0-0), (1-0) and (2-0) bands have previously been identified in interstellar absorption, leaves little doubt that the 3597 \AA interstellar line does indeed arise from the $CH+$ molecule. The new results also indicate that some modification the previously quoted value of the ionization potential of CH may be necessary.