Assignment of the λ1369.13 Diffuse Interstellar Absorption Band and Three Other Far‐Ultraviolet Interstellar Absorption Lines to the CH Molecule

Abstract

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 3 d - X 2 Π 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 3 d - X 2 Π 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 4 d - X 2 Π transition of CH.