D. F. Eggers

Microwave Spectrum, Structure, and Dipole Moment of Cyclopropene

The microwave spectra of four isotopic species of cyclopropene, CH2(CH)2, CH2CDCH, CH2(CD)2, and CDH(CH)2 were assigned and three rotational constants for each isotopic species were determined. From these data the following structural parameters were evaluated: C–C 1.515 A, C=C 1.300 A, C–H (methylene) 1.087±0.004 A, C–H (vinyl) 1.070 A, H–C–H angle 114°42′±10′ and C=C–H angle 149°55′. The uncertainties in the methylene values are the magnitude of a rotation‐vibration interaction correction. The dipole moment of cyclopropene was found to be 0.455±0.01 debye unit.

Fundamental Vibrations and Force Constants in the Partially Deuterated Methyl Halides

Gas‐phase infrared spectra of all eight partially deuterated methyl halides have been obtained; samples were of high isotopic purity. Molecular asymmetry, though quite small, was found to yield significant shifts in the perpendicular structure for the two central Q branches. This was most helpful in the choice of band centers. Observed bands were assigned, including the 72 fundamentals and also 35 overtones and combinations. Although most earlier work was done with samples containing two or more isotopic species, agreement with the present results is quite good in many cases. Evidence for Fermi resonance was found, including two examples in which it occurred below 2000 cm−1. Coriolis coupling between fundamentals was detected in several cases for the fluorides, including a strong resonance between a perpendicular and a parallel vibration. Application of the product and sum rules yielded satisfactory agreement. In a few cases substitution of a heavier atom, such as deuterium for hydrogen, was found to resu...

Infrared Spectrum and Thermodynamic Properties of Gaseous Sulfur Trioxide

The infrared spectrum of sulfur trioxide was obtained under prism resolution in the gaseous state and in xenon matrices at liquid‐nitrogen temperature. In both cases a satisfactory vibrational assignment of the monomeric SO3 spectrum could be made on the basis of a simple D3h symmetry model. The observed gas phase fundamentals were v3(e′) = 1391, v4(e′) = 529, and v2(a2″) = 495 cm—1. The matrix fundamentals were essentially the same as those of the gas phase except that the v2(a2″) mode was shifted to 464 cm—1. A normal coordinate treatment of the SO3 molecule was carried out and potential constants were determined for both Urey‐Bradley and simplified valence force fields. Three weak absorption bands of S3O9 were also detected in the gas‐phase spectrum. From the temperature and pressure variation of the intensities of these bands it was estimated that for the trimerization reaction at 298°K, Kp was approximately 1 atm—2 and ΔH298° was approximately 30 kcal/mole of S3O9. The values of the thermodynamic pro...

Infrared Spectra of Crystalline C2H2, C2HD, and C2D2

The infrared absorption spectra of polycrystalline films of C2H2, C2HD, and C2D2 have been examined at 63°K in the frequency range between 4500 and 450 cm—1. The spectra of the solid state and the gas phase of the various acetylenes are compared and the appropriate vibrational assignments are made. Several absorptions attributable to combinations of lattice modes and molecular fundamentals were found. The observed multiplet structure of the fundamental vibrations indicates that in the low‐temperature modification of C2H2 and C2D2 the molecules are located at sites of C2h symmetry. Spectra of various solid solutions composed of mixtures of isotopic species were obtained and their significance discussed. The effect of isotopic substitution on the splittings in the ν5 region led to the conclusion that the dipole—dipole coupling model is sufficient to explain the observed spectra.

Effect of Centrifugal Distortion on the Shape of the Hydrogen Sulfide Fundamental Infrared Bands

The fundamental infrared vibration bands of hydrogen sulfide exhibit an interesting intensity anomaly characterized by P branches which are much weaker than the corresponding R branches. This work shows that this anomaly is caused by centrifugal distortion of the nonrigid molecule. A formalism based on a semi‐classical approach is used to calculate the vibration—rotational line positions and their intensities. The computed theoretical spectra are in good agreement with the experimental spectra. This formalism also gives a method of determining the relative sign of (∂μ/∂Q) with respect to μ0. The values of (∂μ/∂Q) needed in the calculations were obtained from the experimental integrated band intensities and were found to be (∂μ/∂Q1) = −4.4 esu g−½ and (∂μ/∂Q2) = +8.7 esu g−½.

Vibrational Spectrum of Cyclopropene

The infrared spectra of gaseous cyclopropene and a partially deuterated cyclopropene, and the Raman spectrum of liquid cyclopropene have been determined. The majority of the fundamentals and several overtones and combinations have been assigned. Some force constants based on a simple valence‐force potential function have been calculated.

The ground-state geometry of methyl fluoride

Abstract We have calculated the ground-state geometry for methyl fluoride from microwave spectroscopic rotational constants of five different isotopic species. The use of an A0 value for CH2DF was especially important in enabling us to define the CH distance within fairly narrow limits. The value so obtained is in good agreement with that predicted on the basis of the CH stretching frequency in CHD2F, and it is also consistent with the trend of CH distances in other methyl halides.

The vibrational spectra of solid II ethane and ethane‐d6

Mid‐infrared spectra and Raman spectra are reported for solid II ethane, ethane‐d6, and their mutual solid solutions, at temperatures near 20 K. The results are consistent with a recent x‐ray crystal structure determined for this phase of ethane. Observed vibrations are assigned and compared with several different lattice‐dynamical calculations based on various atom–atom potentials. External vibrations are reproduced moderately well by several potentials, one of which has electrical charges on the atoms. Splittings of internal vibrations are not fit well. Several puzzling discrepancies are noted in the Raman intensities for the solid.

Infrared Spectrum of Deuterium Sulfide

The bending fundamental (v2) of D2S has been investigated under high resolution. Centrifugal‐distortion corrections were applied in the rotational analysis, and transition intensities were computed in both the rigid‐rotor approximation and with the inclusion of classical centrifugal distortion. The inertial constants arising from this analysis for the ground state are A=5.484, B=4.508, C=2.444; for the excited state they are A′=5.616, B′=4.585, C′=2.4216 cm−1, and the v2 band center is 855.45 cm−1. These results together with information derived from previous investigations of D2S and H2S have been used to evaluate the constants in the quadratic expression for the vibrational energy levels and to compute some of the constants in the general expressions for the moments of inertia as a function of vibrational quantum numbers. The experimental values of the inertia defect for the ground state and the v1 and v2 excited states are in good agreement with those predicted theoretically.

Infrared Spectrum of CF3SF5

The infrared spectrum of CF3SF5 has been measured and analyzed between 30 and 4000 cm−1. A band found at 218.5 cm−1 is believed responsible for satellite lines observed previously in the microwave spectrum; the barrier to internal rotation might then be much lower than obtained previously by assuming these satellites were due to torsional oscillation. Twelve of the seventeen fundamentals were assigned in the infrared spectrum and estimates are given for the others. A plausible assignment is given for the overtone and combination bands also observed; this gives no evidence for any of the inactive fundamentals.