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2.
We present evidence for ultra-fast dissociation of molecular ammonia when photo-excited to the N1s→4a 1 core-hole state. This finding is based on resonant Auger spectroscopical results as well as qualitative arguments concerning the photon energy dependence of the Auger structures. Calculations of the excited state potential based on the Z+1 approximation were performed. Both the calculations and the measurements indicate that the most likely fragmentation pathway for the core excited ammonia molecules leads to NH 2* and H fragments. 相似文献
6.
The structure of acetyl cyanide has been determined by making joint use of the electron diffraction intensities measured in the present study and the rotational constants reported by Krisher and Wilson. The thermal average bond distances are: rg(C-H) = 1.116±0.011 Å, rg(CN) = 1.167±0.010 Å, rg(C=O) = 1.208±0.009 Å, rg(=C-C) = 1.477±0.008 Å and rg(C-C methyl) = 1.518±0.009 Å. The bond angles in the zero-point average structure ( rav) are: (C methyl-C=O) = 124.6±0.7°, (C-C-C) = 114.2±0.9°, (C-CN) = 179.2±2.2° and (H-C-H) = 109.2±0.7°. The uncertainties represent the estimated limits of experimental error. The C-C single bond placed between the double and triple bonds is longer than those in vinylacetylene, acrylonitrile and propynal. Other structural parameters are also compared with those in related molecules. The infrared and Raman spectra of this molecule have been measured, and Urey-Bradley force constants have been determined. 相似文献
7.
The rg structure of cyclopentene oxide has been determined by the simultaneous least squares analysis of electron diffraction and microwave spectroscopic data. The investigation has reaffirmed previous studies indicating that the molecule prefers a boat conformation. The methylene and epoxide flap angles obtained are 152.3±2.1° and 104.7±1.0° respectively. Other structural parameters determined are: rg (C-H avg.) = 1.120±0.004 Å; rg (C-C avg.) = 1.538±0.002 Å; rg (C-O) = 1.443±0.003 Å, and rg (C-C) = 1.482±0.004 Å for the carbon-carbon bond in the three membered epoxide ring. These results compare favorably with the reported structures of ethylene oxide and cyclohexene oxide. A tentative rationalization of the unusual boat conformation is also offered. 相似文献
8.
The molecular structure of COBr 2 has been determined as follows by an analysis of electron diffraction intensity: rg(CO) = 1.178 ± 0.009 Å, rg(C-Br) = 1.923 ± 0.005 Å and θ° α(Br-C-Br) = 112.3 ± 0.4°. The uncertainties represent estimated limits of error. The observed systematic trends in the bond lengths and bond angles in carbonyl and thiocarbonyl halides are discussed. 相似文献
9.
The electron diffraction data of cycloheptanone, collected at 371 K, can be explained using a model of partial pseudorotation, with the symmetrical twist—chair as the mean structure. The rg, rα-structure is characterized by r(C-C) = 1.536 Å, r(C=O) = 1.219 Å, r(C-H) = 1.124 Å, xxxCC( sp2)C = 117.3°, xxx(CCC = 115.5° and xxx(HCH = 103.2°. Approximate values for the constants of the pseudorotation potential are included. 相似文献
12.
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, rg(CC) = 1.342 ± 0.002 Å, rg(C-C) = 1.506 ± 0.003 Å, rg(C-H) vinyl = 1.104 ± 0.010 Å, rg(C-H) methyl = 1.117 ± 0.008 Å, ∠(C-CC) = 124.3 ± 0.4°, ∠(CC-H) = 121.3 ± 1.4°, and ∠(C-C-H) = 110.7 ± 0.9°; for trifluoropropene, rg(CC) = 1.318 ± 0.008 Å, rg(C-C) = 1.495 ± 0.006 Å, rg(C-H)= 1.100 ± 0.018 Å, rg(C-F) = 1.347 ± 0.003 Å, ∠(C-CC) = 125.8 + 1.1°, ∠(C-C-F) = 112.0 ± 0.2°, where the valence angles refer to the rav 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 CC and C-C bond distances and the C-CC angles in these and related molecules. Significant differences between the CC, 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. 相似文献
13.
The ineffectiveness of the traditional probe electron-diffraction experiment on free molecules (atoms), which prevents the development of the diffraction structural method in gas phase electron diffraction, has been shown. The application of a molecular beam enabled the determination of a quantitative performance indicator of the scattering process using the given experimental equipment. The quantitative value of the effective cross section on residual gas molecules σ ext( S max, Å ?1) has been suggested as a technical characteristic for the electron diffraction equipment complex. A nomographic chart for determining the number of molecules of any substance has been drawn up in order to obtain a given density of scattered charge on the detector within the maximum sector radium. The author refers to the GED community with the need for agreement on a unified estimation of the efficiency of electron scattering experiment on the free molecules. 相似文献
15.
A joint analysis of electron diffraction and spectroscopic data is carried out for BF 3, PBr 3, AsBr 3, SbCl 3, SeO 2 and ClO 2 in terms of the harmonic force fields. The scheme of analysis was extended to include the following spectroscopic observables: vibrational frequencies, rotational, Coriolis coupling and centrifugal distortion constants and, whenever available, those for the isotopic species. For ClO 2 a simplified anharmonic analysis was also performed, the anharmonic spectroscopic observables being involved in this case. Compelling evidence has been presented that the conventional harmonic approximation for the force field in terms of rectilinear internal coordinates yields the simplest satisfactory representation of diffraction and spectroscopic observations. However, a consistently better fit to experimental data was found when natural curvilinear internal coordinates were used. It is shown here that for the systems considered the joint analysis of data from various sources ensures that reliable and accurate values for equilibrium distances and force field parameters are obtained. The optimized values of spectroscopic constants, structural and force field parameters obtained are presented and compared with those available from the literature. 相似文献
16.
The molecular structure of caffeine (3,7-dihydro-1,3,7-trimethyl-1H-purine-2,6-dione) was determined by means of gas electron diffraction. The nozzle temperature was 185 °C. The results of MP2 and B3LYP calculations with the 6-31G 7 basis set were used as supporting information. These calculations predicted that caffeine has only one conformer and some of the methyl groups perform low frequency internal rotation. The electron diffraction data were analyzed on this basis. The determined structural parameters ( rg and ∠ α) of caffeine are as follows: < r(NC) ring> = 1.382(3) Å; r(CC) = 1.382(←) Å; r(CC) = 1.446(18) Å; r(CN) = 1.297(11) Å; < r(NC methyl)> = 1.459(13) Å; < r(CO)> = 1.206(5) Å; < r(CH)> = 1.085(11) Å; ∠N 1C 2N 3 = 116.5(11)°; ∠N 3C 4C 5 = 121. 5(13)°; ∠C 4C 5C 6 = 122.9(10)°; ∠C 4C 5N 7 = 104.7(14)°; ∠N 9–C 4=C 5 = 111.6(10)°; <∠NCH methyl> = 108.5(28)°. Angle brackets denote average values; parenthesized values are the estimated limits of error (3 σ) referring to the last significant digit; left arrow in parentheses means that this parameter is bound to the preceding one. 相似文献
18.
The cis-Stilbene molecule is found to possess C2 symmetry and may be described as having a propeller-like conformation with the phenyl groups rotated ca. 43° about the C-φ bonds. The deviation from planarity is found to be more extensive than predicted by most theoretical calculations. The steric strain in the molecule is also revealed by large valence angles at the central carbon-carbon double bond (∠CC-C: 129.5°). 相似文献
19.
The photoinduced electron transfer from excited singlet and triplet states of hypocrellins to three electron acceptors, namely, methyl viologen chloride (MV), tetrachloro-p-benzoquinone (TCQ) and 2,3-dichloro-5,6-dicyan-p-benzoquinone (DDQ), has been investigated by fluorescence and time-resolved transient absorption spectra. In acetonitrile solution, DDQ and TCQ quenched the fluorescence and T-T absorption of hypocrellins (HA and HB) efficiently, while neither fluorescence nor T-T absorption of them could be quenched by MV. The quenching resulted from the electron transfer between excited hypocrellins and the electron acceptors was controlled by diffusion. The rate constants of electron transfer from excited singlet and triplet of HA to DDQ are 9.20×10 10 dm 3 mol ?1 s ?1 and 1.28×10 9 dm 3 mol ?1 s ?1, respectively. The transient absorption spectra of the formed radical cations of hypocrellins are reported. 相似文献
20.
The molecular structure of trans-stilbene has been studied by the gas electron diffraction method. Unlike the approximately planar structure with Ci symmetry found for the solid state, the molecule in the gas phase was found to be non-planar and to possess C2 symmetry. The phenyl groups were found to be rotated ca. 30° about the C-φ bonds. The non-planarity of the molecule is, however, not so large as to seriously influence the resonance energy. 相似文献
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