Knowledge Bank

So far only a very limited number of organic nitro-compounds have been investigated in the microwave region. In order to obtain more information about the structure and the internal rotation of a nitro group we have measured the microwave spectrum of nitroethylene $H2C=CHNO2$. Rotational transitions for the ground state and two excited states could be identified. The ground state rotational constants determined from this spectrum are $A=11,811.66Mc,B=4,680.76Mc$, and $C=3,353.78$ Mc. The excited states arise very probably from the torsional motion of the nitro group. From the variations of the inertial defect as a function of the torsional quantum number it was concluded that the nitroethylene molecule has a planar structure. The measurements of the Stark effect for several rotational transitions of the ground and the excited states have confirmed this result and yielded a dipole moment of 3.70 D independent of the torsional state. We have estimated from the relative intensity measurements of the satellites, that the separation of the energy levels from the ground state to the first excited state is $100\pm 20cm\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$, from the ground state to the second excited state $240\pm 40cm-1$. So far we have failed to observe these frequencies in the far infrared due to the easy decomposition of nitroethylene at slightly elevated temperatures.