Intensity borrowing in high J levels of the c 3Π–X 1Σ+ (0–0) transition of carbon monoxide

Several weak new absorption lines in the room temperature spectrum of carbon monoxide have been identified in the 108.9 – 109.0 nm wavelength range. The lines emerge from the long wavelength side of the C 1Σ+–X 1Σ+ (0–0) band and appear to form a single rotational branch. Their most probable assignments are to high J lines (J > 40) of the OP branch of the c 3Π–X 1Σ+ (0–0) band rather than to lines of the k 3Π–X 1Σ+ (2–0) band. The appearance of these lines may be explained by intensity borrowing from the C–X (0–0) transition as a result of mixing between the f1e spin-parity component of the c 3Π state and the C 1Σ+ state, which are predicted to cross in this energy region.