David R. Lide

Calculation of Energy Levels for Internal Torsion and Over‐All Rotation. I. CH3BF2 Type Molecules

Methods are described for calculating the energy levels for the over‐all rotation and internal torsion of molecules consisting of a rigid symmetrical top attached to a rigid asymmetrical framework in such a way that the symmetry axis of the top coincides with a principal axis of the molecule. Probable examples are nitromethane and CH3BF2. Matrix perturbation methods are employed to obtain finite rotational secular equations valid in each of the cases: low barrier, high barrier, low asymmetry. These secular equations are modifications of the ordinary Wang equation for the rigid asymmetric rotor and can usually be solved by the continued fraction method. The symmetry groups applicable to this problem are also discussed.

Microwave Spectrum and Structure of Benzonitrile

The rotational spectrum of benzonitrile has been studied in the one‐centimeter region, and approximately twenty absorption lines have been fitted to the rigid asymmetric‐rotor theory. The principal moments of inertia are 89.370, 326.740, and 416.183 AUA2. The evidence indicates a planar symmetric structure with ring dimensions essentially the same as in benzene. The dipole moment is 4.14±0.05 Debye units.

Improved Measurement of the Electric‐Dipole Moment of the Hydroxyl Radical

The Stark effect of the J=72,2π32, Λ‐doublet transition of OH at 13 438 Mc/sec has been resolved and accurate measurements taken. The dipole moment of OH was determined to be μ=1.660±0.010 D.

The Microwave Spectrum of Methyl Stannane

The microwave spectrum of methyl stannane between 25,500 and 29,000 mc is reported. All of the observed lines may be assigned to the J=1→2 rotational transitions of the isotopic species representing the five most abundant tin isotopes. The dipole moment was found from the Stark splitting to be 0.68±0.03 Debye unit. Insufficient information is available for a complete structure determination, but if tetrahedral angles and a C–H distance of 1.090A are assumed, the data can be fitted with a C–Sn distance of 2.143±0.002A and a Sn–H distance of 1.700±0.015A. The influence of hindered internal rotation on the spectrum is discussed.

A Note on Rotational Line Strengths in Slightly Asymmetric Rotors

Direction‐cosine matrix elements for slightly asymmetric rotors are calculated by a second‐order perturbation treatment around the limiting symmetric rotor. This permits evaluation of the line strengths which are involved in calculations of absorption intensities, Stark effects, and nuclear‐quadrupole couplings in rotational spectra. Explicit formulas are derived for the first‐order terms.