Rotational spectrum and theoretical structure of the carbene HC4N

Following a high-level coupled cluster calculation, the rotational spectrum of the bent HC4N singlet carbene was detected in a supersonic molecular be am by Fourier transform microwave spectroscopy. The three rotational consta nts, the leading centrifugal distortion constants, and two nitrogen hyperfi ne coupling constants were determined to high accuracy. The rotational cons tants agree with those calculated ab initio to better than 0.5%. Like the i soelectronic C5H2 carbene of similar structure, HC4N was found to have fair ly large centrifugal distortion and a large inertial defect. The calculated dipole moment of HC4N is 2.95 D. (C) 1999 American Institute of Physics. [ S0021-9606(99)00339-6].