Laboratory Detection of the C[TINF]7[/TINF]H Radical

The linear carbon chain radical C 7 H has been detected in the same acetylene-argon discharge in which C 8 H was recently observed. Fifty rotational transitions, 23 in the ground 2 Π 1/2 state and 27 in the 2 Π 3/2 state (37 K higher in energy), were measured. Precise values for the rotational, fine structure, and lambda-doubling constants have been derived which allow calculation of the entire microwave and millimeter-wave spectrum to an accuracy of 0.2 km s -1 or better. With the recent discovery of C 8 H in space, C 7 H is an excellent candidate for astronomical detection. To aid future observations, the transition frequencies for the most interesting astronomical lines are tabulated.