Microwave Spectra, Dipole Moment, and Barrier to Internal Rotation of CH3NO2 and CD3NO2

Abstract

The J = 1 to J = 2 and J = 2 to J = 3 transitions for CH3NO2 and CD3NO2 have been assigned for several internal rotational states. The best values of the rotational constants B and C were found to be 10 542.7 and 5876.7 Mc/sec for CH3NO2 and 8697.1 and 5254.3 Mc/sec for CD3NO2. The rotational constant for the NO2 group about the symmetry axis is 13 277.5 Mc/sec. These constants are determined assuming no inertial defect, slightly different values are calculated if other assumptions are made. Some of the assigned lines are a very sensitive function of the low barrier to internal rotation. The barrier term V6 was determined to be 6.03±0.03 calories/mole for CH3NO2 and 5.19±0.03 calories/mole for CD3NO2. The term V12 is less than 0.05 calorie/mole. The dipole moment of CH3NO2 is 3.46±0.02 Debye units.