The microwave spectra of six isotopic species of dimethyl ether were investigated from 8–48 Gc. From the changes in moments of inertia with C13 and O18 substitutions the CO distance and <COC were found to be 1.410±0.003 Å and 111°43′±20′, respectively. The conformation of the methyl groups was determined from the (CH2D) (CH3)O species. Dimethyl ether has C2v symmetry and the methyl groups are staggered with respect to the opposite CO bonds. The data from deuterium substitutions could only be satisfactorily fit by a structure containing asymmetric methyl groups. The two CH distances in this structure differ by 0.009 Å, the < HCH by 49′, and the angle between the CO internuclear line and a perpendicular to its respective hydrogen plane is 2°31′±40′. If an average CH distance of 1.0956 Å is assumed the average <HCH is 109°29′. The structure of the asymmetric methyl groups is shown to be consistent with s and p hybridization of the carbon orbitals. In this scheme the carbons form ``bent bonds'' with the oxygen. From the Stark effect the dipole moment of dimethyl ether was determined to be 1.31±0.01×10—18 esu.

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.

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The microwave spectra of C212H4O, C12C13H4O, C212D4O, C212H4S32, C212H4S34, and C212D4S32 have been determined. For each isotopic species three moments of inertia are obtained. From the 9 moments of inertia for each compound, a set of ``effective'' bond distances and angles (5 in number) have been selected. These ``effective'' bond distances are all self consistent to 0.002A or better. A brief discussion of the resulting structure is given. The dipole moments of C2H4O and C2H4S were determined from the magnitude of the Stark splitting.