Munetaka Nakata

Vibrational analysis of ethylamines: Trans and gauche forms

Abstract Starting from force constant values calculated by an ab initio MO method ( 4-31G(N ∗ ) ), and by adjusting the diagonal elements, a practical force constant matrix (F) has been reached which could explain the observed infrared and Raman spectra (in the frequency range lower than 2000 cm−1) of the gauche form of the ethylamine CH3CH2NH2 molecule and five isotopic species CH313CH2NH2, CH3CH215NH2, CH3CD2NH2, CH3CH2ND2, and CD3CD2NH2. The F matrix for the trans form of ethylamine was constructed by transferring ab initio 4-31G(N ∗ ) values and by revising diagonal elements with conversion factors whose values are equal to the corresponding values of gauche form. A nearly complete set of assignments was achieved of the vibrational bands of ethylamines, observed so far in the spectral range 2000–100 cm−1. In matrix isolation spectroscopy, two bands assignable to the NH2 wagging vibrations of gauche and trans forms have been found at 775 and 782 cm−1, respectively, for CH3CH2NH2. They are at 768 and 774 cm−1, respectively, for CD3CD2NH2. From the intensity changes of these bands observed on changing the nozzle temperature in the matrix formation, the energy difference ΔE (gauche-trans) of these two conformers has been estimated to be 100 ± 10 cm−1.

Structure of dichlorine monoxide as studied by microwave spectroscopy. Determination of equilibrium structure by a modified mass dependence method

Abstract The microwave spectra of four isotopic species of dichlorine monoxide (OCl2) have been observed, and the rotational constants have been obtained. The rm structure for each isotopic species has been determined by Watsons method. The equilibrium structure has been estimated by taking proper averages of rm structures to be r e (OCl) = 1.69587(7) A and ∠eClOCl = 110.886(6)°. The general applicability and the merit of the present method for estimating the equilibrium structure are pointed out.

Average and equilibrium structures of methyl flouride studied by electron diffraction. A joint analysis with rotational constants and cubic force constants

Abstract Electron diffraction intensity of methyl fluoride was measured and analyzed jointly with the rotational constants, A o and B o , of the normal species. The following structure was derived: r g (CF) = 1.391(1) A, r g (CH) = 1.108(1) A and β z (FCH) = 108.7(2)°, where the numbers in parentheses represent estimated limits of error. The effective anharmonic constants were derived using the rotational constants and the l -type doubling constants; the cubic force constants calculated by Kondo using a 6-311G** (MP2) basis set were also incorporated in the analysis. The following equilibrium structure was derived from the r z structure and the effective anharmonic constants: r e (CF) = 1.383(1) A, r e (CH) = 1.086(2) A and β e (FCH) = 108.8(3)°.

Molecular structure of phosgene as studied by gas electron diffraction and microwave spectroscopy: The rs, rm, and re structures

Abstract The microwave spectra of eight isotopic species of COCl2 have been observed, and the following rotational constants have been obtained: An analysis of the rotational constants has resulted in the rs and rm structures. The equilibrium structure, re, has been estimated by combining the rm parameters derived according to Watsons method and the re bond distances estimated in our recent electron-diffraction and spectroscopic studies to be r e (CO ) = 1.1756 ± 0.0023 A , r e (CCl ) = 1.7381 ± 0.0019 A , ∠eClCCl = 111.79 ± 0.24°.

Some thoughts on the vibrational modes of toluene as a typical monosubstituted benzene

Abstract Characteristic features of the normal modes of toluene, a typical monosubstituted benzene, are discussed in comparison with the normal modes of benzene itself. New notations for the normal modes of benzene and monosubstituted benzenes are proposed.

Molecular structure of phosgene as studied by gas electron diffraction and microwave spectroscopy: The rz structure and isotope effect

Abstract The rz structure of phosgene has been determined by a joint analysis of the electron diffraction intensity and the rotational constants as follows: r z ( CO ) = 1.1785 ± 0.0026 A , r z ( CCl ) = 1.7424 ± 0.0013 A , ∠z;ClCCl = 111.83 ± 0.11°, where uncertainties represent estimated limits of experimental error. The effective constants representing bond-stretching anharmonicity have been obtained from an analysis of the isotopic differences in the rz structure: a 3 ( CO ) = 2.9 ± 0.9 A −1 , a 3 ( CCl ) = 1.6 ± 0.4 A −1 . The equilibrium bond distances have been estimated from the rz structure for the normal species and from the anharmonic constants to be r e ( CO ) = 1.1756 ± 0.0032 A , r e ( CCl ) = 1.7381 ± 0.0019 A .

Molecular structure of carbonyl fluoride as studied by gas electron diffraction and microwave data

Abstract The molecular structure of carbonyl fluoride has been determined by electron diffraction. The results have been used in conjunction with the rotational constants reported by Carpenter in a combined structure analysis. The values so obtained are rz (C=O) = 1.1717 ± 0.0013 A, rz (C-F) = 1.3157 ± 0.0005 A, and ∠zF-C-F = 107.71 ± 0.08°. These agree with the corresponding parameters estimated by Carpenter from the rotational constants alone. The effective constants, α3, representing the cubic anharmonicity of bond stretching vibrations have been estimated.

Molecular structure of thiocarbonyl chloride as studied by gas electron diffraction

Abstract The average molecular structure of thiocarbonyl chloride, CSCl 2 , has been determined from a combination of electron diffraction data and published microwave data. The following values were obtained: r z (CS) = 1.602 ± 0.005 A, r z (C-Cl) = 1.728 ± 0.003 A, and ∠ z Cl-C-Cl = 111.2 ± 0.3°, where the uncertainties represent estimated limits of experimental error. The effective constants, a 3 , representing the cubic anharmonicity of bond-stretching vibrations are estimated to be a 3 (CS) = 2.6 ± 1.8 A −1 and a 3 (C-Cl) = 2.1 ± 0.5 A −1 .

Equilibrium structure and anharmonic potential constants of phosgene derived from rotational constants and electron diffraction intensity

The third-order anharmonic constants of phosgene are determined from the rotational constants of the six fundamental vibrational states, those of eight isotopic species, and the rz structure obtained from the electron diffraction intensity by analyzing the changes in the average structures. The equilibrium structure is obtained as re(CCl = 1.7365(12) A, re(CO) = 1.1766(22) A, and ∠e(ClCCl) = 111.91(12)°.

Structures of 1,2-dimethylhydrazine conformers as determined by microwave spectroscopy and gas electron diffraction

Abstract Microwave spectra of the inner-outer and outer-outer conformers of 1,2-dimethylhydrazine were assigned. Then rotational constants and the electron diffraction intensity were used for a joint analysis, from which their CNNC dihedral angles, 88.4 ± 0.7° and 164.2 ± 14°, and abundance ratio at room temperature, 62 ± 8% : 38 ± 8%, respectively, were determined.