Electron-Diffraction Study of the Structures of C2H4 and C2D4

Abstract

lines are partially blended. Thus, it appears that Chiu's equations give very reasonable predictions for the intensities of this mixed magnetic-dipole-e1ectric-quadrupole transition.Wilkinson and Mulliken,2 using relatively poor uncalibrated photographic data on the a lIIgf-X ll;g+ system and employing line-strength formulas developed only for a ll;g+f-ll;g+ transition 9 (admittedly very tentatively), estimated Q/D=0.15, which is of the order of magnitude of the value obtained here. This presumably more precise value of 0.33 leads to a value of X in Eq. (1) of 9 a.u. instead of 4.5 a.u. given previously.The above determined ratio is certainly not in disagreement with the crude theoretical prediction of Q/ D"-'0.1 mentioned earlier. Nevertheless, Condon 7 has studied such transitions for p2, p3, and p4 configura-9 H. M. James and A. S. Coolidge, Astrophys. J. 85, 438 (1938).THE JOURNAL OF CHEMICAL PHYSICS 2683 tions in atoms, and has found quite variable values for this ratio. It does appear that a careful theoretical study of the vibronic matrix elements for this particular transition would be most helpful.It is perhaps worth mentioning that the line-intensity study reported here is one of the few experimental tests on intensities in forbidden transitions in diatomic molecules and only the fourth in the vacuum ultraviolet. lO ACKNOWLEDGMENTSThe authors wish to express their appreciation to Mr.The structures of ethylene and deuteroethylene were investigated by electron diffraction to resolve apparent discrepancies between earlier diffraction and spectroscopic studies. Satisfactory agreement with the previous diffraction study was found for five of the six molecular parameters determined but a difference of five standard deviations was encountered for the C-H bond length. Mean bond lengths and standard errors for C2H, obtained in the present investigation were rg (CH)=1.1030±0'()()l s A and r g (CC)=1.3369± 0.0016 A. Corresponding lengths for C2D, were r g (CD)=1.099±0.003 A and r g (CC)=1.338±0.003 A.Bond angles, corrected for shrinkage effects, were L CCH= 121.4±0.6° and L CCD= 121.4±0.8°. The new diffraction results are compared with mean bond lengths and angles calculated from spectroscopic rotational constants taking rotation-vibration interactions into account. Excellent agreement is found. Significant differences exist, however, between the conventional bond-length parameters derived by spectroscopy and diffraction. Root-mean-square amplitudes of vibration were also determined by diffraction, and these agreed satisfactorily with amplitudes calculated from vibrational frequencies.

A polarized, twisted, ethylene: structure of 3,3-bis(methylthio)-2-nitro-2-propene-1-nitrile, C5H6N2O2S2

“…* Some important torsion angles are provided in Table 2. The Bartell, Roth, Hollowell, Kuchitsu & Young, 1965]. It is also observed that the bonds C (2) (3)i~,] bond lengths are also slightly shorter than the value of 1.764 (1)/~, found in tetrakis(methylthio)ethylene measured at 238K (Collins & Davis, 1978).…”

The liquid structure of tetrachloroethene: Molecular dynamics simulations and reverse Monte Carlo modeling with interatomic potentials

“…The structure of small organic liquid molecules can be investigated by different experimental techniques (for example electron 7 , neutron 8 and X-ray diffraction 9 , infrared 10 , Raman 11 and NMR 12 spectroscopy) or using theoretical approaches like ab initio calculations 13 , density functional theory 14 or integral equations 15 . Different simulation methods are available, as well, that apply interaction potential functions: molecular dynamics (MD) 16 and standard (Metropolis) Monte Carlo 17 simulations are the best known examples.…”

Structure of allyl 1-deoxy-1-[(1-methyl-2-benzoylvinyl)amino]-α-D-fructofuranoside

“…The N-C2 bond distance of 1.325 (9)/~ is much shorter than the value of 1.452 (2)A reported by Ammon, Mazzocchi, Regan & Colicelli (1979), and indicates partial doublebond character; the planar conformation for this group also indicates that the state of hybridization of the N atom is sp 2. The C2=C3 bond length is 1.398 (10)/~ [normal double bond in ethylene 1.336 (2),~ (Bartell, et al, 1965)], and the twist angle around this bond is 1.6 (10) °. The low twist angle is due to the strong intermolecular H bonding between the NH and CO groups.…”

“…A variety of substituted ethylenes have C=C bonds significantly longer than the bond in ethylene [1.336 (2)A; Bartell, Roth, Hollowell, Kuchitsu & Young, 1965;Kuchitsu 1966], e.g. trivinylborane, 1.370 (6)/~ (Foord, Beagley, Reade & Steer, 1975).…”