Differentielle Streuquerschnitte bei der Wechselwirkung neutraler Moleküle

An apparatus to measure differential scattering cross sections using crossed molecular beams is described and results for the scattering of potassium atoms by different heavy atoms and molecules are presented. The experimental data are compared with theoretical calculations for a Buckingham-(exp-six)-potential and the parameters of this potential are determined. To carry out this comparison, it was necessary to average the existing calculations of E. A.Mason over the Maxwellian velocity distribution in the potassium beam. These averaged differential cross sections are tabulated for various angles and temperatures in the appendix of the present paper. Using crossed beams of molecules containing halogens, we can observe chemical reactions. Methods to determine total and differential reaction cross sections are discussed.     

Zur Quantentheorie der stimulierten RAMAN-Streuung in Molekülkristallen. II. Spezielle Fälle eines stationären RAMAN-Oszillators

Two kinds of stationary RAMAN oscillators are investigated theoretically for molecular crystals. The calculations are done firstly for the generation of one first order anti-STOKES mode and secondly for the generation of one second order STOKES mode. By using a quantum theoretical model described in an earlier paper for treatment of molecular crystals RAMAN scattering is assumed to be polariton scattering. Within this framework coupled nonlinear equations for the polariton operators of the excited modes are derived, stationary occupation numbers for the different modes and threshold conditions are calculated. The influence of phase fluctuations of the pump wave on the line widths of the RAMAN modes are investigated.     

Comparison of measured total integral cross sections for noble gas dimer-atom systems with IOSA calculations

Experimentally determined total integral cross sections for noble gas dimer-atom systems, involving the energetically accessible channels of excitation, exchange and dissociation are compared with theoretical values calculated using a simple formula. This simple formula is derived using the multichannel optical theorem and the infinite order sudden approximation (IOSA). The potential is well approximated by the sum of known pair potentials. Setting the IOSA parameters L and K equal to the angular momentum and the wave number of the initial channel, respectively, the largest error between the experimental and theoretical results is about 10%. We noticed that a proper choice of the relation between K and the collision energy greatly reduces this error; a possible explanation cannot be given.     

Totale Streuquerschnitte für den Stoß von H2, D2 und He an den Edelgasen Ne,Ar, Kr und Xe im thermischen Energiebereich

The velocity dependence of the total elastic cross section has been measured for the scattering of H₂, D₂, and He beams by Ne, Ar, Kr, and Xe gases. Velocity-selected beams were attenuated by gas in a scattering chamber. A universal detector, with a magnetic mass separator, was used in conjunction with lock-in techniques. The results are compared with quantum mechanical calculations using a Lennard-Jones-(12.6)-potential, and employing suitable averaging over experimental velocity distributions. Potential parameters are presented. These are in good agreement with those expected from other methods of measurement.     

Stereochemical aspects of proton chemical shifts. VII. The γ effects of hydroxyl,methoxyl and methyl substituents

The ¹H NMR chemical shifts of some hydroxy, methoxy or methyl substituted trans-decalins, trans-1, 3-dioxadecalins and cyclohexanes are reported. It is concluded that the replacement in a g⁺g⁺ H? C? C? C? H fragment of one hydrogen by hydroxy, methoxy or methyl results in a modest (0.1 ppm) upfield shift of the other hydrogen atom. Experimental limitations to the transferability of shift increments from one molecular environment to another are demonstrated. The syntheses of 1α,5β-dimethoxy- and 1β,5α-dimethoxy-trans-decalin are given.     

A Duality for Spin Verlinde Spaces and Prym Theta Functions

The paper proves canonical isomorphisms between Spin Verlindespaces, that is, spaces of global sections of a determinantline bundle over the moduli space of semistable Spin_n-bundlesover a smooth projective curve C, and the dual spaces of thetafunctions over Prym varieties of unramified double covers ofC.     

60]fullerene-stoppered porphyrinorotaxanes: pronounced elongation of charge-separated-state lifetimes

A series of Sauvage-type porphyrinorotaxanes containing [60]fullerene stoppers have been synthesized by a convergent route. Photoinduced energy transfer and electron-transfer reactions in these rotaxanes yield long-distance charge-separated radical-pair states, whose lifetimes in solution at ambient temperatures are as high as 32 mus, depending on the distance between the fullerene and zinc porphyrin chromophores.     

Metal coordination to the formal P=N bond of an iminophosphorane and charge-density evidence against hypervalent phosphorus(V)

The iminophosphorane Ph(2)P(CH(2)Py)(NSiMe(3)) (1) was treated with deprotonating alkali metal reagents to give [(Et(2)O)Li[Ph(2)P(CHPy)(NSiMe(3))]] (2), [[Ph(2)P(CH(2)Py)(NSiMe(3))]Li[Ph(2)P(CHPy)(NSiMe(3))]] (3) and [[Ph(2)P(CH(2)Py)(NSiMe(3))]Na[Ph(2)P(CHPy)(NSiMe(3))]] (4). We report their coordination behaviour in solid-state structures and NMR spectroscopic features in solution. Furthermore, we furnish experimental evidence against hypervalency of the phosphorus atom in iminophosphoranes from experimental charge-density studies and subsequent topological analysis. The topological properties, correlated to the results from NMR spectroscopic investigations, illustrate that the formal P=N double bond is better written as a polar P(+)--N(-) single bond. Additionally, the effects of metal coordination on the bonding parameters of the iminophosphorane and the related anion are discussed.     

Multicomponent redox gradients on photoactive electrode surfaces

Redox gradients have been used to tailor the arrangement of photoactive ITO-electrodes at the molecular level.