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We have obtained from the concentration dependent depolarized Rayleigh scattering experiment (using a Fabry–Perot interferometer) the single particle reorientation relaxation time τs of CH2Br2 to be 3.4±0.2 psec at 20 °C. This time is a factor of 2.0 greater than the Raman correlation time τm obtained for the ν2(A1) Raman band. Moreover, the Raman correlation times τm obtained for the other A1 bands do not have the same values as that obtained for the ν2 band. This difference is due to the fact that the nonreorientational correlation functions Ciso(t) and Cβ(t) do not have the same time dependence, hence making the usual Raman line shape analysis difficult to apply to CH2Br2. From depolarized Rayleigh scattering, we have found in neat CH2Br2 that the classical Stokes–Einstein relation for rotational diffusion does not apply, despite the fact that τRay was found to vary linearly with η/T. However, when using the slip boundary condition and modeling CH2Br2 as an ellipsoid, we have found reasonable agreement...

The orientational and density fluctuation spectra of liquid 1,2,5‐thiadiazole were determined by the light scattering technique. The viscosity and density of the pure liquid were also measured as a function of temperature. Results of concentration dependent studies of 1,2,5‐thiadiazole in an optically isotropic solvent having the same viscosity as the pure liquid show that the pair orientational correlation is very small. The experimentally determined reorientational relaxation times were found to be close to the prediction of the slip model for rotational diffusion. The sound velocity of the pure liquid was found to decrease linearly with increasing temperature. The sound dispersion was found negligible in the GHz frequency region.

A number of deuterated pyrroles have been prepared and their microwave spectra recorded. For each isotopic species the two 1→2 transitions observable around 20 000 MHz were localized together with a number of Q‐lines in the 17 400—26 000 MHz region scanned. For all isotopic molecules rotational constants were calculated. In this way seven mutually independent numerical data were obtained which is insufficient for a direct calculation of the nine geometrical parameters of pyrrole. Additional assumptions as to the length of the two C, H bonds lead to definite models for pyrrole.

Microwave spectra of benzonitrile, C6H5CN, and 9 isotopic species are reported. Moments of inertia of these 10 molecules are combined to give the rs structure of benzonitrile. The final structure is: C(1)C(2) = 1.391 A, C(2)C(3) = 1.393 A, C(3)C(4) = 1.400 A, C(1)C(7) = 1.455 A, C≡N = 1.159 A, C(2)H(2) = 1.069 A, C(3)H(3) = 1.082 A, C(4)H(4) = 1.081 A, C(6)C(1)C(2) = 122.5°, C(1)C(2)C(3) = 118.45°, C(2)C(3)C(4) = 120.3°, C(3)C(4)C(5) = 120.0°, C(1)C(2)H(2) = 121.8°, C(4)C(3)H(3) = 119.9°.

2‐ and 3‐monodeutero, 3,3′‐dideutero, and tetradeuterothiophene have been prepared and their microwave spectra recorded together with the microwave spectrum of ordinary thiophene (C4H4S). Lines originating from the 4% content of C4H4S34 and the 2% content of C3C13H4S in ordinary thiophene (both the 2‐ and the 3‐C13 species) were also identified. For all isotopic species rotational constants of high accuracy were obtained. The total material is sufficient for a complete determination of all the 8 geometrical parameters of thiophene.

The microwave spectra of seven isotopic species of propylene have been studied in order to obtain an accurate molecular structure. The complete rs (substitution) structure has been calculated. The more important parameters are: r(C=C)=1.336±0.004 A,r(C–C)=1.501±0.004 A, ≰CCC=124.3∘±0.3∘. The structure is compared with those of related molecules. It is concluded that no difference can be detected in the double‐bond lengths in ethylene, propylene, and the vinyl halides. The CC single‐bond length in propylene is indistinguishable from that in acetaldehyde and other acetyl compounds, and is 0.025 A shorter than the CC distance in saturated hydrocarbons. In the =CH2 group in propylene, the CH bond trans to the methyl group appears slightly shorter than the cis CH bond; a similar effect occurs in the vinyl halides.

Low frequency Raman spectra (20–400 cm−1) are presented of formamide dissolved in dimethylsulfoxide (DMSO). The concentration of formamide ranges from 2%–75% (v/v). The two formamide bands at 110 and 190 cm−1 in the neat liquid exhibit only smaller frequency shifts upon dilution. The intensities of both bands are proportional to the concentration of formamide. The conclusion is, that the linear chain structure, found in neat liquid formamide, is conserved in the DMSO solution. Raman spectra of the NH‐stretching region (2950–3500 cm−1) confirm this hypothesis.

The microwave spectrum of the symmetric tops, CF3C≡C–CH3 and CF3C≡C–CD3, has been investigated. Excited vibrational state transitions were observed, but the l‐type doublet fine structure was not resolvable. Since lines originating from species containing C13 in natural abundance were identified, only two assumptions were necessary in order to determine the 7 structural parameters. The parameters giving the best fit with the experimental data are: d(C,F) = 1.340, d(C(1), C(2)) = 1.455 = d(C(3), C(4)), d(C(2), C(3)) = 1.189, and d(C,H) = 1.097 A and the angles ∠F–C–F = 106°08′ and ∠H–C–H = 108°30′.