Lamb-dip millimeter-wave spectrum, structure and dipole moment of HCCCCF

The ground state rotational spectrum of HCCCCF has been observed in the mil limeter-wave region using the Lamb-dip technique and very accurate values o f the spectroscopic constants have been obtained. Moreover, the observation of the ground state rotational spectra of the four C-13 monosubstituted is otopomers and of the deuterated species of fluorodiacetylene have enabled t he determination of the r(0) and r(s) molecular structures. The electric di pole moment of HCCCCF has been determined by observing the Stark spectrum o f the J = 3 <-- 2 rotational transition. The equilibrium geometry and the d ipole moment have been evaluated using different ab initio methods and comp arison between experimental and theoretical results has been made.