2001ApJ...555..472W

The three unidentified interstellar lines λλ1368.74, 1369.13, and 1370.87 are here assigned to the CH molecule, including the diffuse interstellar band (DIB) at 1369.13 Å. A consistent rotational assignment of the interstellar lines and the 3d-X ²Π laboratory spectrum is presented. The predominant broadening mechanism of the lines appears to be predissociation, which is found to be greater for lines with upper levels of d parity, including the DIB, than for lines with upper levels of c parity. The oscillator strength of the 3d-X ²Π transition is estimated to be f~0.033. Using the theoretical n^* dependence of the parameters together with the wavenumber of the observed laboratory Q-form branch, an unidentified interstellar line at 1270.96 Å is assigned to the strongest line of the 4d-X ²Π transition of CH.