Microwave spectra of the ground and excited vibrational states of isotopic species of nitroethylene

Rotational spectra of nitroethylene, four deuterium and six ¹³C species have been measured and analysed in the frequency range from 8 to 26 GHz. Rotational transitions in the ground state, in progressions of excited states of the NO₂ torsional mode ν₁₈, in the in-plane skeletal bending mode ν₁₃, and in doubly excited states σ₁₃+ν₁₃+ν₁₈ν₁₈ could be assigned for nitroethylene and its deuterated species. The spectra of the ¹³C isotopic species were observed in natural abundance and their assignments have partly been checked by microwave — microwave (mw — mw) double resonance. All the spectra in each of the different vibrationally excited states were found to acceptably obey a rigid rotor pattern with centrifugal distortion, corresponding to a high barrier for the NO₂ internal rotation. Rotational constants and inertia defects all show the same qualitative dependence on the internal state. The ground state rotational constants of all isotopic species have been used to determine a refined molecular structure.