Recoil-ion momentum distribution for He(e,2e)He+-and He(e,3e)He++-reactions

Using Recoil-Ion Momentum Spectroscopy (RIMS) we have measured the momenta of recoiling target ions in He(e,2e)He⁺- and He(e,3e)He⁺⁺-reactions at impact energies between 270 ev and 3200 eV. The recoil-ion momentum reflecting the sum momentum of all outgoing electrons was determined for the first time in all three spatial dimensions separately for single and double ionization by electron impact. The data are compared to results of a nCTMC-calculation.     

A(1,3)-strain mediated epimerization of 2e,3e,5e,6e-tetraarylpiperidin-4-one oximes

A series of tri- and tetraarylpiperidin-4-one oximes were synthesized from 2e,3e,6e-tri- and 2e,3e,5e,6e-tetraarylpiperidin-4-ones, respectively. In the case of the latter compounds, oximation is accompanied by epimerization at C-5 to avoid the A(1,3)-strain between the oxime OH group and the 5e-aryl ring of the initially formed oxime resulting in 2e,3e,5a,6e-tetraarylpiperidin-4-one oximes. 1H, 13C and 2D NMR spectroscopic data were employed to characterize and investigate the stereochemistry of these compounds.     

Regio- and stereoselective synthesis of enantiomerically pure [60]fullerene tris-adducts with an inherently chiral e,e,e addition pattern

The synthesis and flash column chromatographic separation of enantiomerically pure tris-adducts of C60 with an e,e,e-addition pattern is achieved via cyclopropanation with chiral D3-symmetrical cyclo-tris(malonate) tethers.     

(e,2e) Spectroscopy of methane

Measurements are reported on the spectroscopy of methane using the symmetric (e,2e) technique at energies of 600 eV and 1200 eV. The angular correlations of the states with separation energies of 14.2 and 23.1 eV have been measured and compared with the orbital wavefunctions of Snyder and Basch and with some earlier data at 400eV. The angular correlation of the configuration interaction state at 31 eV shows that this state definetely results from the removal of an electron in the 2a₁ orbital. Other structure at high separation energy is also identified with this orbital. Relative strengths of the It₂ and 2a₁ states are compared and found to be in agreement with the theory at 1200eV.     

Dynamical (e,2e) studies of tetrahydrofurfuryl alcohol

Cross section data for electron scattering from DNA are important for modelling radiation damage in biological systems. Triply differential cross sections for the electron impact ionization of the highest occupied outer valence orbital of tetrahydrofurfuryl alcohol, which can be considered as an analogue to the deoxyribose backbone molecule in DNA, have been measured using the (e,2e) technique. The measurements have been performed with coplanar asymmetric kinematics at an incident electron energy of 250 eV, an ejected electron energy of 20 eV, and at scattered electron angles of -5°, -10°, and -15°. Experimental results are compared with corresponding theoretical calculations performed using the molecular 3-body distorted wave model. Some important differences are observed between the experiment and calculations.     

UV, VUV and soft X-ray photoabsorption of dimethyl ether by dipole (e,e) spectroscopies

Absolute UV and VUV photoabsorption oscillator strengths (cross-sections) for the valence shell discrete and continuum regions of dimethyl ether (CH₃OCH₃, DME) have been measured from 5 to 32 eV using high resolution (HR) (0.05 eV f.w.h.m.) dipole (e,e) spectroscopy. A wide-range spectrum, spanning the UV, VUV and soft X-ray regions, from 5 to 200 eV has also been obtained at low resolution (LR) (1 eV f.w.h.m.), and this has been used to determine the absolute oscillator strength scale by employing valence shell Thomas–Reiche–Kuhn (i.e., S(0)) sum-rule normalization. The presently reported HR and LR absolute photoabsorption oscillator strengths are compared with previously published data from direct photoabsorption measurements in those limited energy regions where such data are available. Evaluation of the S(−2) sum using the presently reported absolute differential photoabsorption oscillator strength data gives a static dipole polarizability for dimethyl ether in excellent agreement (within 0.5%) with previously reported polarizability values. Other dipole sums S(u), (u=−1,−3,−4,−5,−6,−8,−10), and logarithmic dipole sums L(u), (u=−1 to −6), are also determined from the presently reported absolute differential photoabsorption oscillator strength data using dipole sum rules.     

Dynamical (e, 2e) studies using tetrahydrofuran as a DNA analog

Triple differential cross sections for the electron-impact ionization of the outer valence orbital of tetrahydrofuran have been measured using the (e, 2e) technique. The measurements have been performed with coplanar asymmetric kinematics, at an incident electron energy of 250 eV and at an ejected electron energy of 10 eV, over a range of momentum transfers. The experimental results are compared with theoretical calculations carried out using the molecular three-body distorted wave model. The results obtained are important for gaining an understanding of electron driven processes at a molecular level and for modeling energy deposition in living tissue.     

Examination of (e,2e) scattering models by comparison of momentum profiles of noble gases between experiment and theory

Momentum profiles have been measured for the two outermost atomic orbitals of noble gases, Ar, Kr and Xe, at incident electron energy of about 2 keV using a newly developed multichannel (e,2e) spectrometer. The experimental results exhibit significantly improved statistics compared with those achieved in previous studies while covering a wide range of momenta up to 3.6 a.u. The results are compared with theoretical calculations using four (e,2e) scattering models, the plane-wave impulse and Born approximations (PWIA and PWBA), and the distorted-wave impulse and Born approximations (DWIA and DWBA). The DWIA and DWBA scattering models have been found to satisfactorily reproduce the experimental momentum profiles in terms of both shape and intensity over the entire momentum range covered, indicating the importance of distorted wave effects for quantitatively describing (e,2e) reaction.     

Satellite structures and momentum distributions in binary (e, 2e) spectroscopy of N2O

The (e, 2e) coincidence technique has been applied in studying the valence shell of N₂O. The assignment of some satellite structures is discussed.     

Molecular Structure of 5-Methylchrysene-7,8-dihydro-7,8-trans-(e,e)-diol

The crystal structure of the weak carcinogen 5-methylchrysene-7,8-dihydro-7,8-trans-(e,e)-diol is reported. This molecule contains a distorted bay region as a result of the presence of the 5-methyl group as found in 5-methylchrysene and 5,6- and 5, 12-dimethylchrysene. One torsion angle in this bay region is 20. The two hydroxyl groups of this molecule form hydrogen bonds throughout the crystal along theb direction. This is similar to the packing in other crystal structures of dihydrodiols of polycyclic aromatic hydrocarbons, each hydroxyl group both receiving and donating one hydrogen bond.     

An investigation of valence shell orbital momentum profiles of difluoromethane by binary (e,2e) spectroscopy

The electron binding energy spectra and momentum profiles of the valence orbitals of difluoromethane, also known as HFC32 (HFC-hydrofluorocarbon) (CH(2)F(2)), have been studied by using a high resolution (e,2e) electron momentum spectrometer, at an impact energy of 1200 eV plus the binding energy, and by using symmetric noncoplanar kinematics. The experimental momentum profiles of the outer valence orbitals and 4a(1) inner valence orbital are compared with the theoretical momentum distributions calculated using Hartree-Fock and density functional theory (DFT) methods with various basis sets. In general, the shapes of the experimental momentum distributions are well described by both the Hartree-Fock and DFT calculations when large and diffuse basis sets are used. However, the result also shows that it is hard to choose the different calculations for some orbitals, including the methods and the size of the basis sets employed. The pole strength of the ionization peak from the 4a(1) inner valence orbital is estimated.     

An (e,2e) study of ammonia: Binding energies and momentum distributions of valence electrons

The valence shell electronic structure of NH₃ is studied in an (e,2e) experiment with symmetric non-coplanar geometry. The momentum distributions obtained for the separate orbitals are compared with those calculated from several approximate wavefunctions. The 3a₁ distribution is found to be particularly sensitive to the form of the wavefunction.     

Electrophilic substitution reactions in 4H-benzo[d,e,f]carbazole

The behavior of 4H-benzo[d,e,f]earbazole and its N-aeetyl derivative in various electrophilic substitution reactions (e.g. nitration, nitrosation, bromination, Friedel-Crafts acylations) has been investigated, and a number of new derivatives of this heterocycle (some of which are to be tested as potential carcinogens and enzyme-inducers) have been synthesized.     

Biocatalytic Routes to Enantiomerically Enriched Dibenz[c,e]azepines

Biocatalytic retrosynthetic analysis of dibenz[c,e]azepines has highlighted the use of imine reductase (IRED) and ω‐transaminase (ω‐TA) biocatalysts to establish the key stereocentres of these molecules. Several enantiocomplementary IREDs were identified for the synthesis of (R )‐ and (S )‐5‐methyl‐6,7‐dihydro‐5H ‐dibenz[c,e]azepine with excellent enantioselectivity, by reduction of the parent imines. Crystallographic evidence suggests that IREDs may be able to bind one conformer of the imine substrate such that, upon reduction, the major product conformer is generated directly. ω‐TA biocatalysts were also successfully employed for the production of enantiopure 1‐(2‐bromophenyl)ethan‐1‐amine, thus enabling an orthogonal route for the installation of chirality into dibenz[c,e]azepine framework.     

Synthesis of(7e,9e,11e,13e)-18,18,18-trifluororetinal (all-trans 5-trifluoromethylretinal)

All-trans-18,18,18-trifluororetinal (2) was synthesized through trifluorocyclocitral (3) as a key intermediate.     

A Convenient Method for the Preparation of 4(e)-Hydroxy-and 4(e)-Methoxyadamantan-2-ones

Hydrolysis or methanolysis of 4(a)-(trifluoromethyl-sulfonyloxy)adamantan-2-one affords 4(e)-hydroxy-or 4(e)-methoxyadamantan-2-one, respectively, as major product, both of which are easily separated from minor by-products.     

Outer valence orbital momentum distributions of carbon dioxide by binary (e,2e) spectroscopy

The outer valence orbital momentum distributions of CO₂ have been reinvestigated using a high momentum resolution (0.1 a_o^?1 fwhm) binary (e,2e) spectrometer operated at 1200 eV impact energy under the non-coplanar symmetric scattering condition. Generally good agreement of the measured momentum distributions with theoretical momentum distributions calculated using literature SCF double-zeta quality wavefunctions has been obtained for the 1π_g, (1π_u + 3σ_u) and 4σ_g orbitals. Although there is a reasonable agreement of the measured momentum distributions with earlier low momentum resolution (0.4 a_o^?1 fwhm) non-coplanar measurements at 400 eV impact energy reported by Cook and Brion, given the large differences in the momentum resolutions much more definitive results are obtained in the present study. In particular, the significantly higher momentum resolution clearly shows the mixed s-p character of the 4σ_g orbital. The present study also gives a much better agreement with theory in the case of the 4σ_g momentum distribution. For each orbital the calculated and where possible the experimentally determined spherically averaged momentum distributions are compared and contrasted with their respective two-dimensional momentum and position density maps. These together with three-dimensional surface plots at selected constant density values of the four outermost orbitals are used to provide a detailed comparison of momentum-space bonding and orbital properties with their more familiar position-space counterparts in the CO₂ triatomic molecule. The calculated momentum-space density contour maps of the core orbitals exhibit rather large density oscillations and the feasibility of future experiments is discussed.     

Ground state correlations in H2 measured by the (e,2e) technique

The relative intensities for exciting the 1sσ_g, 2pσ_u, 2pπ_u, and 2sσ_g states of H₂ are measured in a 1200 eV noncoplanar symmetric (e,2e) experiment on H₂. Momentum distributions are obtained at separation energies corresponding to the various transitions. The ratio of transition probability to the excited states relative to the ground state is strongly dependent on the ion recoil momentum q, having a minimum value of approximately 2% at small q. The excited state cross sections are sensitive to electron correlation effects and the data are compared with calculated cross sections using a configuration interaction wavefunction for H₂.     

Ionization potentials and electron momentum distributions for SiF4 valence-shell orbitals: an (e,2e) spectroscopic investigation and Green's function study

Ionization potentials and electron momentum distributions of SiF₄ valence-shell orbitals have been measured by means of (e,2e) spectroscopy. SCF calculations and a Green's function study have been performed on the same molecule. A comparison between experimental and theoretical results shows that a significant interaction of 2p F with 3d Si orbitals occurs.     

NX(a 1Δ, X=F、Cl、Br)分子结构与ωe～Re关联模型

基于不少双原子分子的稳定激发态系列中存在已知ωe而未给出Re的现象,本文提出了ωe～Reα=C的理论模型,对近60个双原子分子的光谱数据进行了论证,并与量子力学计算结果进行了比较.结果表明,该模型具有通用性与可靠性.结合NX(a 1Δ)替代O2(a 1Δg)的新激光系统可能性研究需要,应用CIS、B3LYP与MCSCF方法,在6-311＋g(3df)基水平计算了NX(X=F、Cl、Br)第一激发态（a 1Δ）的结构,导出了解析势能函数.