LABORATORY DETECTION OF THE C8H RADICAL

The C8H radical has been detected in an argon-acetylene discharge, con clusively confirming the identification by Cernicharo and Guelin in th e accompanying Letter of their new linear molecule in IRC+10216. In ad dition to the ground (2) Pi(3/2) rotational ladder, the (2) Pi(1/2) la dder 19 cm(-1) above ground has been detected, and the entire fine str ucture-rotational spectrum calculated. The standard (2) Pi Hamiltonian fits the laboratory measurements of more than 30 radio lines between 80 and 100 GHz to high accuracy; yields precise values for the rotatio nal, fine structure, and lambda-doubling constants; and allows the ast ronomically most interesting lines in the radio spectrum to be predict ed to an uncertainty of 0.1 km s(-1) or better.