Michiro Hayashi

Microwave spectrum, structure and nuclear quadrupole coupling constant tensor of ethyl chloride and vinyl chloride

Abstract Microwave spectra of ethyl chloride and its eleven isotopic species and vinyl chloride and its nineteen isotopic species have been measured. Least-squares analyses for the observed frequencies give rotational, quartic centrifugal distortion constants and the nuclear quadrupole coupling constants, χ+ and χ−, of all the species of these molecules. The rs structures have been well established from the observed moments of inertia. The principal nuclear quadrupole coupling constants are calculated from the χ+ and χ− values. The principal χ constants of ethyl chloride and vinyl chloride are discussed and compared.

Microwave spectrum, structure, and dipole moment of vinyl fluoride

Abstract Microwave spectra of vinyl fluoride and its nine isotopic species were measured in order to establish the r s structure. Stark-effect measurements of several low- J transitions were carried out for the normal and three deuterated species. The dipole moment of the normal species of vinyl fluoride is μ a = 1.284 ± 0.004, μ b = 0.712 ± 0.012, and μ total = 1.468 ± 0.007 D and makes an angle of 1°7′ with the CF bond.

Revised rs structures of three dialkyl ethers

Abstract Oxygen-18 enriched samples of ethyl methyl ether, methyl propyl ether and diethyl ether have been prepared and their microwave spectra measured. The rs structures of the trans or trans-trans isomers of these molecules have been re-evaluated from the reported and newly obtained moments of inertia and a comparison made. The rs structures of some related molecules have also been compared.

Reinvestigation of molecular structures of dimethyl silane and dimethyl sulfide

Abstract The microwave spectra of twelve isotopic species of dimethyl silane and eleven isotopic species of dimethyl sulfide were measured. For the species whose spectra exhibit multiplet structures due to the methyl internal rotation, the rotational, quartic centrifugal distortion constants and the quantities related to the methyl internal rotation were determined simultaneously from the observed frequencies of the multiplets. The rs structures of these molecules were well established from the moments of inertia determined. The analyses and discussions on the tilted methyl group were made carefully by comparing the present results with the ones available in the literature.

Microwave spectrum, structure, dipole moment, and internal rotation of fluoromethyl methyl ether

Abstract Microwave spectra of fluoromethyl methyl ether and its 10 isotopically substituted species were measured. The r s structure of this molecule was determined from the observed moments of inertia. Structural parameters obtained for this molecule, which was in the gauche form, were compared with those of the analogous molecules. Dipole moments of the normal and two deuterated species were determined by Stark-effect measurements. For the normal species, the dipole moment is 1.744 ± 0.029 D making an angle of 100°54′ with the OCH 2 bond toward the CF direction and lies in the plane whose dihedral angles with the FCO and COC planes are 114°9′ and 44°56′, respectively. The barrier to internal rotation of the methyl group was calculated taking into account the coupling effect with the skeletal torsion using the observed splitting data of the spectra in the ground, first excited methyl torsional, and skeletal torsional states. The barrier, skeletal torsional frequency, and coupling term were determined to be V 3 = 1538 ± 40 cal/mole, ω t = 158 ± 4 cm −1 , and V s = 490 ± 500 cal/mole, respectively.

Reinvestigation of microwave spectrum of dimethyl ether and rs structures of analogous molecules

Abstract Microwave spectra of dimethyl ether and its sixteen isotopic species have been measured. For species with singlet spectra, a least-squares analysis of observed transition frequencies gave rotational and five quartic centrifugal distortion constants. For species with multiplet spectra due to the methyl internal rotation, a least-squares analysis of observed multiplet frequencies gave not only unperturbed rotational and five quartic centrifugal distortion constants but also the quantities related to the methyl internal rotation. The r s structures from (CH 3 ) 2 O, CH 3 OCD 3 , and (CD 3 ) 2 O species as the parent species, respectively, were compared with one another. The proposed r s structure has been established from all the species measured and was compared with the r s -like structure obtained by a diagnostic least-squares method and with the reported structure. The r s structure of the present molecule was compared with the reported structures of dimethyl sulfide and dimethyl silane in relation to the tilt phenomenon. The r s structure of dimethyl sulfide was revised based on the present comparison.

Microwave spectrum and structure of cis-methyl vinyl ether

Abstract Microwave spectra of cis -methyl vinyl ether and its 14 isotopically substituted species have been measured. The r s structure of this isomer has been determined from the observed moments of inertia. The dipole moment and its direction in the molecule have been determined by Stark effect measurements of the spectra for three isotopic species. The barrier to internal rotation of the methyl group has been determined from the A - E splittings of the spectra in the excited methyl torsional states. The structure of the present isomer is discussed in comparison with those of the analogous molecules. An ab initio MO calculation has been carried out for the structure obtained, the discussions being extended to the direction of the dipole moment in the molecule.

The rs structures of propyl fluoride and differences in structures between rotational isomers

Abstract Microwave spectra of trans and gauche propyl fluoride and its isotopically substituted species have been measured. The rs structures of the trans and gauche isomers of this molecule are determined from the observed moments of inertia. It is found that the CCC angle values are largely different between two isomers, while the CCF angle values stay unchanged. The rs structures of ethyl fluorosilane and ethylmethlyl sulfide are re-examined in order to compare the results with those of propyl fluoride. The differences in the structural parameter values between the rotational isomers are discussed for the present molecules and the analogous molecules such as ethanethiol and ethaneselenol.

Microwave spectrum and internal rotation of 2-butyne-1, 1, 1-d3 (dimethylacetylene), CH3C≡CCD3

The rotational transitions of CH3C≡CCD3 have been observed for J=13←12, 15←14, 18←17, 19←18, 20←19, 22←21, 23←22, and 26←25 using a source‐frequency modulation microwave spectrometer with a 3.7 m long free space absorption cell maintained at −50 to −60 °C. The observed spectrum clearly shows the effect of internal rotation with a small potential barrier. The expression for the rotational transition frequency derived by Kirchhoff and Lide [J. Chem. Phys. 43, 2303 (1965)] using a second‐order perturbation theory for the contributions of the internal rotation was employed in analyzing the observed spectrum, and the least‐squares analysis has yielded the rotational constant B=2982.4980±0.0011 MHz and a few centrifugal distortion constants. The barrier height to internal rotation has been estimated to be 5.62±0.16 cm−1.

Microwave spectrum of ethyl fluoride and structure of CH3MH2X type molecules

Abstract Microwave spectra of ethyl fluoride and its 19 isotopic species were measured to establish the r s structure. Stark-effect measurements of several low- J transitions were carried out for the normal and CD 3 CH 2 F species. The molecular structures, dipole moments, and nuclear quadrupole coupling constant tensors of CH 3 MH 2 X type molecules (M = C, Si, Ge, X=F, Cl, Br, I) were compared. For molecules whose structures had been obtained by different choices of assumptions, the r s coordinate values were re-calculated from the reported data with assumptions similar to those of the present analysis. The systematic shifts of the structural parameter values and of the directions of dipole moments, and the principal axes of the nuclear quadrupole coupling constant tensors, are discussed.