Tsutomu Fukuyama

Average structures of butadiene, acrolein, and glyoxal determined by gas electron diffraction and spectroscopy

Abstract The structures of butadiene, acrolein, and glyoxal have been investigated with the main purpose of studying the variation in the lengths of the central C-C bonds. In order to derive as reliable structures as possible, the electron diffraction intensities obtained in the present study and the rotational constants for several isotopic species reported in the literature have been analyzed by a least-squares method which combines them as joint observables. The method is based on the conversion of the electron-diffraction r a distances into the r ° α distances and that of the effective ground-state rotational constants into the average rotational constants.

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.

Molecular structures of propene and 3,3,3-trifluoropropene determined by gas electron diffraction

Abstract The structures of propene and 3,3,3-trifluoropropene have been studied by electron diffraction intensities measured in the present study and rotational constants reported in the literature. The following average structures have been determined: For propene, r g (CC) = 1.342 ± 0.002 A, r g (C-C) = 1.506 ± 0.003 A, r g (C-H) vinyl = 1.104 ± 0.010 A, r g (C-H) methyl = 1.117 ± 0.008 A, ∠(C-CC) = 124.3 ± 0.4°, ∠(CC-H) = 121.3 ± 1.4°, and ∠(C-C-H) = 110.7 ± 0.9°; for trifluoropropene, r g (CC) = 1.318 ± 0.008 A, r g (C-C) = 1.495 ± 0.006 A, r g (C-H)= 1.100 ± 0.018 A, r g (C-F) = 1.347 ± 0.003 A, ∠(C-CC) = 125.8 + 1.1°, ∠(C-C-F) = 112.0 ± 0.2°, where the valence angles refer to the r av structure, and the uncertainties represent estimated limits of experimental error. A simple set of quadratic force constants for each molecule has been estimated. Regular trends have been observed in the CC and C-C bond distances and the C-CC angles in these and related molecules. Significant differences between the CC, C-C and C-F distances and the C-C-F angle in trifluoropropene and in hexafluoroisobutene reported by Hilderbrandt et al. have been indicated.

Molecular structure and puckering potential function of cyclobutane studied by gas electron diffraction and infrared spectroscopy

The electron diffraction intensity of cyclobutane was measured and analyzed conjointly with the rotational constant, B0=0.355 82(11) cm−1, determined by an analysis of FTIR spectra of the ν14 (CH2 scissoring, B1g) and ν16 (CH2 rocking, A2u) bands. The rz structure was determined to be rz (C–C)=1.552±0.001 A, rz (C–H)=1.093±0.003 A, αz (∠HCH)=106.4±1.3°, and the ring dihedral angle, θz =27.9±1.6°; the rg distances of the C–C and C–H bonds are 1.554±0.001 and 1.109±0.003 A, respectively. The uncertainties represent estimated limits of error. The rocking angle βz between the bisectors of the adjacent H–C–H and C–C–C angles was found to be 6.2±1.2°, the axial C–H bonds in the 1,3 positions being tilted towards each other. The coefficient of coupling of the ring‐puckering and CH2‐rocking motions was estimated to be βz/θz =0.22±0.05. The combination and difference sideband structures appearing in the ν14 band due to the puckering mode ν6 were analyzed. The puckering energy levels thus obtained were consistent w...

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.

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°.

Molecular structures of isobutene and 2,3-dimethyl-2-butene as studied by gas electron diffraction

Abstract The structures of isobutene and 2,3-dimethyl-2-butene have been studied by gas electron diffraction. For isobutene the rotational constants obtained by Laurie by microwave spectroscopy have also been taken into account. Leastsquares analyses have given the following r g bond distances and valence angles ( r av for isobutene and r α for dimethylbutene): for isobutene, r (CC) = 1.342±0.003 A, r (C-C)= 1.508±0.002A, r (C-H, methyl) = 1.119±0.007 A, r(C-H, methylene) = 1.095±0.020 A, ∠(C-CC) = 122.2±0.2°, ∠(H-C-H) = 107.9±0.8°, and ∠(C-C-H) 121.3±1.5°; for dimethylbutene, r (CC)= 1.353 ±0.004 A, r (C-C) = 1.511±0.002 A, r (C-H) = 1.118± 0.004 A, ∠(C-CC)= 123.9±0.5°, and ∠(H-C-H)= 107.0±1.0°, where the uncertainties represent estimated limits of experimental error. The bond distances and valence angles in these molecules and in related molecules are compared with one another. The CC and C-C bond distances increase almost regularly with the number of methyl groups, and the C-C bonds in isobutene and dimethylbutene are shorter than those in acetaldehyde and acetone by about 0.01 A. Systematic variations in the C-CC angles suggest the steric influence of methyl groups.

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 .

Structure of acrylonitrile as determined by electron diffraction and spectroscopy

Abstract The structure of acrylonitrile has been determined by making use of the electron-diffraction intensities obtained in the present study together with the rotational constants reported in the literature. The thermal-average bond lengths are: rg(C-C) = 1.438 ± 0.003 A, rg(CC) = 1.343 ± 0.004 A, rg(CN) = 1.167 ± 0.004 A and rg(C-H) = 1.114 ± 0.007 A. The bond angles in the zero-point average structure are: ∠ (CC-C) = 121.7 ± 0.5°, ∠ (C-CN) = 178.2 ± 1.0° and ∠ (CC-H) = 119.7 ± 2.1°. The uncertainties represent the limits of experimental error. The carbon-carbon single bond length in acrylonitrile is nearly equal to, or slightly longer than, that in vinylacetylene. In order to investigate the origin of the observed differences in the C-C bond lengths of acrylonitrile, vinylacetylene and propynal, bond orders have been calculated by the Pariser-Parr-Pople method. The effect of the core resonance integral, β, on the relative magnitude of bond orders has been discussed. The observed differences in r(C-C) are found to be much larger than the estimates by means of empirical or theoretical order-length relations.

Penning ionization electron spectroscopy and photo-electron spectroscopy of molecular solids. II. Ammonia and water

Abstract The Penning ionization electron spectra (PIES) and ultraviolet photoelectron spectra (UPS) of ammonia and water molecules condensed on a cold metal substrate have been measured using thermal He*(2 3 S , 2 1 S ) metastable atoms and He(I) (58.4 nm) photons. The shifts of the observed positions of the PIES peaks relative to those of the UPS peaks in the condensed phase are roughly equal to the corresponding shifts in the gas phase. The relative intensities of the 3 a 1 and 1 e orbital peaks are reversed in the PIES and UPS for both gaseous and condensed ammonia; the origin of this reversal is interpreted as the difference between the interactions with metastable atoms and photons. On the other hand, the relative intensities of the 3 a 1 orbital peak in the PIES and UPS for condensed water decrease as compared to the gas-phase spectra. This implies participation of the 3 a 1 orbital of water in the hydrogen bonding.