DISCOVERY OF THE C8H RADICAL

Searching for C7H and C8H in the carbon star envelope IRC+10216, we ha ve identified 10 lines with harmonically related frequencies and with regularly increasing intensities (3 lines in the IRAM 3 mm spectral su rvey and 7 lines in the 7 mm Nobeyama survey of Kawaguchi et al., 1995 ). The rest frequencies can be closely fitted with the standard expres sion for the energies of a linear molecule with a rotational constant B = 586.676 MHz, a distortion constant D = 6.3 Hz, and half-integer qu antum numbers J. The value of B is within 0.1% of that predicted by Pa uzat et al. (1991) for the (2) Pi ground state of C8H and the value of D typical of a linear acetylenic chain of C8H's weight. Since the hal f-integer J numbers are also consistent with a (2) Pi state, we conclu ded that we had very probably discovered C8H. In the an accompanying L etter, McCarthy et al. report the detection of 30 lines of our new rad ical in an acetylene discharge and confirm they arise from C8H.