Microwave spectrum of 3-bromopropene in the excited torsional states

The microwave spectra in the excited states of the CC torsion for the ⁷⁹Br and ⁸¹Br isotopic species of 3-bromopropene were measured in the frequency region 15.3–23.7 GHz. The a-type R-branch and b-type Q-branch rotational transitions in the first and second excited states of one conformer, skew, have been assigned and analyzed. Analysis of the spectrum yields the rotational constants and the nuclear quadrupole coupling constants. From relative intensity measurements the energy differences associated with the CC torsion, between the ground and first excited state, the ground and second excited state have been found to lie 109 and 206 cm^?1, respectively.