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The far-infrared spectra of ON 35 Cl and ON 37 Cl were recorded from 20 to 100 cm −1 at a resolution of 0.004 cm −1 . Thirteen pure rotational Q branches were assigned for each molecule in the ground vibrational state from which the rotational constants A and the distortion constants φ K and φ K were obtained utilizing previously reported values of the constants B and C from microwave studies. Rotational Q branches were also observed for both molecules in two vibrationally excited states. Ab initio calculations up to those using fourth-order perturbation (MP4) with configuration interaction utilizing the 6-31G* basis set were carried out. Optimized geometries obtained at this level are compared with those obtained with smaller basis sets without configuration interaction and with the experimentally determined values. Force constants were calculated which are compared with the values previously reported. The potential energy distributions and quartic distortion constants were obtained at all levels of ab initio calculations up to MP2/6-31G*.

The Raman spectra of gaseous, liquid and solid S(SiH 3 ) 2 and S(SiD 3 ) 2 have been recorded from 50 to 3500 cm −1 , and the infrared spectra of the gas and solid have also been investigated. A vibrational assignment is proposed and a normal coordinate calculation carried out using a modified valence force field.

The infrared spectrum at a resolution of 0.06 cm−1 has been recorded for vinylsilane. Vibrational-rotational analysis has been carried out on ν6, ν13, ν15, and the strongly coupled pair of ν12 and ν19. The rotational constants and some of the distortion constants have been determined for ν6, ν13, and ν15, whereas higher resolution of 0.004 cm−1 was required to obtain similar data from the coupled pair of ν12 and ν19. These data are compared to the ground state constants previously obtained from the microwave spectrum.

The Raman and IR spectra of diallyl sulfide and diallyl disulfide in the liquid and solid state are reported and examined in order to determine their most stable conformations. In both the liquid and solid state, the allyl moieties in both molecules are in a “gauche” conformation in which the sulfur atoms and the terminal vinyl carbons probably form a dihedral angle of between 105° and 120°. In the liquid state, there are two possible S-S rotational conformers of diallyl disulfide. The “gauche” conformer with a C-S-S-C dihedral angle of approximately 70° is 242±24 cal mol−1 more stable than the “near-cis” conformer which probably has a C-S-S-C dihedral angle of approximately 25°. Only the “gauche” S-S rotational conformer of diallyl disulfide exists in the solid state. Additionally, in the liquid state, there are two C-S rotational conformers for each molecule. The “gauche” conformer corresponds to a C-C-S-C (diallyl sulfide) or C-C-S-S (diallyl disulfide) dihedral angle of 70° and the “trans” conformer corresponds to a C-C-S-C or C-C-S-S dihedral angle of 180°. For diallyl sulfide the “trans” C-S conformer is 260±26 cal mol−1 more stable than the “gauche” C-S conformer while for diallyl disulfide the “gauche” C-S conformer is 358±20 cal mol−1 more stable than the “trans” C-S conformer. In the solid state, both C-S conformers exist for diallyl sulfide but only the “gauche” C-S conformer exists for diallyl disulfide.

Infrared spectra (from 4000 to 400 cm−1) of solid, liquid and gaseous 1,1-diethylcyclopropane and Raman spectra of the condensed phases of this compound have been recorded. Evidence for two conformational isomers, one of which vanishes in the polycrystalline solid phase, is found in the spectral data for the liquid phase. It has been concluded that these two rotational isomers are the gauche/gauche conformers which arise when the two methyl groups are displaced in a conrotatory sense (C2 symmetry) and a disrotatory sense (Cs symmetry) from a hypothetical cis/cis (C2υ) structure. These conclusions are consistent with the conformational results previously obtained for ethylcyclopropane and ethyloxirane. In addition, from the variable temperature liquid phase Raman intensity measurements, the C2 rotamer of 1,1- diethylcyclopropane has been calculated to be 1.1 ± 0.2 kcal/mole more stable than the Cs form, and is the sole conformer remaining in the solid phase. Tentative vibrational assignments, in agreement with those for related molecules, are proposed for the major spectral bands of 1,1-diethylcyclopropane.

The ν 1 , ν 2 , and ν 3 fundamentals of nitrosyl chloride, ON 35 Cl, have been recorded with a Fourier transform interferometer at an apodized resolution of 0.004 cm −1 . The data have been analyzed together with previous microwave data for the ground vibrational state to yield improved molecular parameters for the (100), (010), and (001) vibrational states. The main results (in cm −1 ) are: v 1 = 1 v 2 = 1 v 3 = 1 A 2.892513(18) 2.941109(9) 2.931514(12) B 0.1922820(7) 0.1906560(8) 0.1904847(9) C 0.1800373(7) 0.1783946(8) 0.1784287(8) ν i 1799.7316(2) 595.8518(2) 331.9707(2) Additionally, the values for a number of the centrifugal distortion constants have been obtained for each of these normal modes.

The i.r. (4000-200 cm −1 ) and Raman (4000-50 cm −1 ) spectra of gaseous and solid 2-fluoroethylamine have been recorded along with the Raman spectra of the neat liquid and a TMS solution. These data have been interpreted on the basis of at least four conformations in the gas phase and one conformation in the crystalline solid. Conformers identified as Gg ′ and Gt which exhibit intramolecular hydrogen bonds are the most stable forms in the gas phase and coexist with the Gg and Tg conformers. In the condensed phases, intermolecular hydrogen bonding becomes a dominant factor, and only the Gg conformer remains in the solid. The conformer stabilities determined here are discussed in terms of theoretical calculations and experimental data for similar molecules.

Raman spectra of the condensed phases of dicyclopropylmethane have been recorded. In addition, i.r. spectra of this compound have been obtained for all three phases. From the appearance of spectral doublets in the liquid phase Raman (and i.r.) spectra, one member of each of which vanishes upon crystallization, it has been concluded that, in the liquid state, DCPM exists as an equilibrium mixture of at least two conformers. Based upon the spectral results for DCPM, and upon the conformational preferences of a number of related molecules, it has been concluded that these two conformers are the C 2 and C s gauche/gauche rotational isomers, with the C 2 form being the one which remains in the solid phase. From a variable temperature study of liquid phase Raman peaks, it has been determined that the C 2 conformer of DCPM is more stable than the C s conformer by 0.93 ± 0.10 kcal/mole. In addition, it appears that the C 2 rotamer of DCPM also predominates in the gaseous phase. Tentative assignments of the major spectral bands of DCPM have also been proposed.

The Raman spectra of liquid and solid dl-bisoxirane and the infrared spectra of all three phases have been recorded. The microwave spectrum has been studied in the X- and R-band frequency regions. The vibrational data indicate that the molecule exists as a mixture of at least two conformations in the fluid state. The more stable conformer, which has a trans orientation of the two oxirane rings and persists as the only conformer in the crystalline solid state, has also been observed in the microwave spectrum of the vapor. The rotational constants of the ground vibrational state are (in MHz) A = 10998.186, B = 2340.413, and C = 2126.233. From Stark effect measurements, the dipole moment component μb (along the symmetry axis) is found to be 3.43 ± 0.01 D. Rotational transitions and the Stark effect for two excited vibrational states have also been measured and analyzed. A second conformer, which is 0.23 ± 0.08 kcal/mole (0.96 ± 0.33 kJ/mole) less stable than the trans conformer in the liquid state, is identified as a near-gauche conformer whose dihedral angle is probably between 40° and 50°. The possibility of an additional conformer is considered, and the structure of dl-bisoxirane is discussed in terms of similar molecules.

The vibrational spectra of cyclopropylamine have been reconsidered; the results are consistent with our earlier studies describing a trans/gauche conformational equilibrium. The conformer having the amino protons trans to the ring CC bonds is more stable than the gauche conformer. The equilibrium in cyclopropylamine is discussed and contrasted with a recent report in which only one conformer was identified.