Interstellar C2 molecules toward Zeta Ophiuchi

Ten weak interstellar absorption lines of the (2-0) Phillips band of C2 near 8760 A are detected in the spectrum of Zeta Ophiuchi. All of the lines have equivalent widths smaller than 2 mA, and originate from the six lowest rotational levels of C2. The resulting total column density is equal to about 1.7 x 10 to the 13th/sq cm, and the excitation temperature is 130 + or - 10 K.