Kozo Kuchitsu

Comparison of Molecular Structures Determined by Electron Diffraction and Spectroscopy. Ethane and Diborane

Gas‐phase average structures for the ground‐vibrational state (rz) for ethane and diborane have been determined by a critical comparison of the experimental results obtained from electron diffraction (average internuclear distances rg) and those obtained from high‐resolution infrared and Raman spectroscopy (rotational constants Bz(α)). Experimental values have been taken from the recent literature and converted into the average structure (rzor rα0). The rg and rα0 distances determined from electron diffraction carry uncertainties less than those in the rz distances determined from rotational constants, because the latter structures are very sensitive to assumptions about the unknown isotope differences in the structures. On the other hand, the average moments of inertia from spectroscopy are much more precise than those calculated from diffraction internuclear distances. Examinations of the data have led to the following rz structures with standard errors: For C2H6, rz(C–H) = 1.0957 ± 0.002 A, rz(C–C) = 1...

The role of isotopic differences in the determination of molecular structure. A supplementary note on the structure of acrolein

Abstract The discrepancy between the r a o and r z structures of acrolein reported in a previous study has been removed by taking into account small isotopic differences in the distances among the carbon and oxygen atoms. The effect of uncertainties in the isotopic differences on the determination of the average structure is examined, and a general method for deriving the best possible structure from electron-diffraction and spectroscopic data is suggested. The r g bond distances in butadiene, acrolein, and glyoxal are compared with one another.

A nomenclature for Λ‐doublet levels in rotating linear molecules

It is proposed that the two Λ‐doublet levels of linear molecules with nonzero electronic orbital angular momentum be labeled Λ(A’) and Λ(A‘), e.g., Π(A’) and Π(A‘) for Π states, etc., according to the following prescription: All series of levels in which the electronic wave function at high  J is symmetric with reflection of the spatial coordinates of the electrons in the plane of rotation will be designated Λ(A’) for all values of J, and all those for which the electronic wave function is antisymmetric with respect to reflection will be denoted Λ(A‘). It is emphasized that this notation is meant to supplement, and not replace, the accepted spectroscopic e/f labeling and the parity quantum number. The utility of the Λ(A’)/Λ(A‘) notation is that it is of most relevance in the mechanistic interpretation of reactive or photodissociative processes involving open‐shell molecules.

Structure of cyclohexane determined by two independent gas electron-diffraction investigations

Abstract The results of two independent electron-diffraction investigations of cyclohexane are compared. By averaging the results the following parameters and error limits are obtained: r g (CC) = 1.536±0.002 A, r g (CH) = 1.121±0.004 A, and ∠CCC = 111.4±0.2°.

Calculation of the Average Structure of Ethylene

The average structure of ethylene in the ground vibrational state has been calculated from the internuclear distances (rg) obtained from electron diffraction by making corrections for the effect of atomic displacements perpendicular to the equilibrium bond directions and the centrifugal distortion, and from the rotational constants A0, B0, and C0 obtained from infrared and Raman spectra by making corrections for the interactions of vibration and rotation. Good agreement is observed between the diffraction and spectroscopic average structures, and the following average structure of C2H4 has been determined: rz(C=C) = 1.335±0.003 A, rz(C–H) = 1.090±0.003 A, and ∠zC–C–H = 121.7°±0.4°.

B–F Bond Distance of Boron Trifluoride Determined by Gas Electron Diffraction

The B–F bond distance rg of BF3 was determined by gas electron diffraction to be 1.3133±0.0010 A. The corresponding rotational constant B0 was calculated to be 0.3449±0.0006 cm−1 from the rg distance by the use of the theory of rotation—vibration interaction. This value was consistent with the rotational fine structure of the v2 infrared band reported by Nielsen, when slight changes in his J assignments were made. The reanalysis of his spectral data led to B0=0.3449 cm−1 and DJ=(4.1±0.4)×10−7 cm−1. The latter constant was in good agreement with the theoretical estimate, 4.13×10−7 cm−1. The zero‐point average distance, rz(B–F), of BF3 was thus determined from the diffraction and infrared experiments to be 1.3112±0.001 A.

The Mean Amplitudes of Thermal Vibrations in Polyatomic Molecules. I. CF2=CF2 and CH2=CF2

A normal coordinate treatment based on the potential function of Urey‐Bradley type has been applied to CF2=CF2 and CF2=CH2 molecules by taking into account the repulsions between nonbonded atoms in addition to the valence force field. The mean‐square amplitudes of thermal vibration of the atomic distances in these molecules have been calculated by the use of the normal coordinates and compared with those obtained by I. Karle and J. Karle from the electron diffraction investigation.

Band contour analysis of the ν1 and ν5 fundamentals of formaldehyde

Abstract Infrared ν 1 and ν 5 bands of H 2 CO in the CH stretching frequency region were measured with the resolution of 0.3 cm −1 . Rotational structures of these bands were analyzed as asymmetric-top bands by means of band-contour calculations and least-squares fits. The band origins and the rotational constants of the upper states were determined. The band origin of ν 5 , 2843.24 ± 0.03 cm −1 , is in good agreement with that obtained by Blau and Nielsen using a symmetric-top approximation, whereas the ν 1 band origin, 2782.40 ± 0.07 cm −1 , is significalnty higher than the value 2766.4 cm −1 assigned by them. Small anomalous shifts were observed in the ν 1 band, indicating the presence of Coriolis interactions with other states. Possible cases are discussed. Equilibrium rotational constants were calculated by the use of the α constants determined in our present and previous studies, and the r e structure was estimated to be r e (CH) = 1.099 ± 0.009 A , and φ e (HCH) = 116.5 ± 1.2°, on the assumption that r e (CO) = 1.203 ± 0.003 A .

Unit for the Precise Measurement of Electron Diffraction Intensities by Gas Molecules

An apparatus for the precise measurement of electron intensity diffracted from gas molecules has been constructed. Care has been taken to define camera distances precisely by installing a table, to which the nozzle and the photographic plate can be fixed firmly, and to eliminate extraneous scattering by designing a suitable electron-optical system and by inserting a brass ring with a folded wall covered with soot into the sector race. A critical examination by the use of carbon dioxide has shown that the structure can be determined with the accuracy of one thousandth of an angstrom with the present apparatus.

The anharmonic constants and average structure of ammonia

Abstract The cubic and quartic potential constants for NH 3 and ND 3 have been calculated by assuming intramolecular potential functions of internal coordinates and by means of the nonlinear transformation of the internal coordinates into the normal coordinates. The ordinary F matrix elements in the internal-symmetry coordinate system and the Morse-like parameters representing the anharmonicity of the NH bond-stretching vibrations are taken into account in the valence force model, and in addition the hydrogen—hydrogen potential terms are assumed in the vander Waals model. A majority of the cubic constants, the vibration—rotation interaction constants α, and the l -type doubling constants q t calculated by these models agree essentially with the experimental values reported by Benedict and Plyler. The comparison has indicated that almost all the third-order potential constants in the internal coordinate system ignored in the valence force model should have small negative values, as observed for several bent XY 2 molecules. Possible orders of magnitude of these constants have been estimated. The vibrational anharmonic constants χ have been estimated in a similar manner from the cubic and quartic constants. The zero-point average structure is derived from the experimental rotational constants to be: r z (NH) = 1·024 0 A, α z (HNH) = 107·3 2 °, and r z (ND) = 1·020 6 A, α z (DND) = 107·2 2 °.