ion. The oxidative addition mechanism was originally proposed22i because of the lack of a strong rate dependence on polar factors and on the acidity of the medium. Later, however, the electrophilic substitution mechanism also was proposed. Recently, the oxidative addition mechanism was confirmed by investigations into the decomposition and protonolysis of alkylplatinum complexes, which are the reverse of alkane activation. There are two routes which operate in the decomposition of the dimethylplatinum(IV) complex Cs2Pt(CH3)2Cl4. The first route leads to chloride-induced reductive elimination and produces methyl chloride and methane. The second route leads to the formation of ethane. There is strong kinetic evidence that the ethane is produced by the decomposition of an ethylhydridoplatinum(IV) complex formed from the initial dimethylplatinum(IV) complex. In D2O-DCl, the ethane which is formed contains several D atoms and has practically the same multiple exchange parameter and distribution as does an ethane which has undergone platinum(II)-catalyzed H-D exchange with D2O. Moreover, ethyl chloride is formed competitively with H-D exchange in the presence of platinum(IV). From the principle of microscopic reversibility it follows that the same ethylhydridoplatinum(IV) complex is the intermediate in the reaction of ethane with platinum(II). Important results were obtained by Labinger and Bercaw62c in the investigation of the protonolysis mechanism of several alkylplatinum(II) complexes at low temperatures. These reactions are important because they could model the microscopic reverse of C-H activation by platinum(II) complexes. Alkylhydridoplatinum(IV) complexes were observed as intermediates in certain cases, such as when the complex (tmeda)Pt(CH2Ph)Cl or (tmeda)PtMe2 (tmeda ) N,N,N′,N′-tetramethylenediamine) was treated with HCl in CD2Cl2 or CD3OD, respectively. In some cases H-D exchange took place between the methyl groups on platinum and the, CD3OD prior to methane loss. On the basis of the kinetic results, a common mechanism was proposed to operate in all the reactions: (1) protonation of Pt(II) to generate an alkylhydridoplatinum(IV) intermediate, (2) dissociation of solvent or chloride to generate a cationic, fivecoordinate platinum(IV) species, (3) reductive C-H bond formation, producing a platinum(II) alkane σ-complex, and (4) loss of the alkane either through an associative or dissociative substitution pathway. These results implicate the presence of both alkane σ-complexes and alkylhydridoplatinum(IV) complexes as intermediates in the Pt(II)-induced C-H activation reactions. Thus, the first step in the alkane activation reaction is formation of a σ-complex with the alkane, which then undergoes oxidative addition to produce an alkylhydrido complex. Reversible interconversion of these intermediates, together with reversible deprotonation of the alkylhydridoplatinum(IV) complexes, leads to multiple H-D exchange

Activation of c-h bonds by metal complexes

The application of electrostatic lenses is demonstrated to give a substantial improvement of the two-dimensional (2D) ion/electron imaging technique. This combination of ion lens optics and 2D detection makes “velocity map imaging” possible, i.e., all particles with the same initial velocity vector are mapped onto the same point on the detector. Whereas the more common application of grid electrodes leads to transmission reduction, severe trajectory deflections and blurring due to the non-point source geometry, these problems are avoided with open lens electrodes. A three-plate assembly with aperture electrodes has been tested and its properties are compared with those of grid electrodes. The photodissociation processes occurring in molecular oxygen following the two-photon 3dπ(3Σ1g −)(v=2, N=2)←X(3Σg −) Rydberg excitation around 225 nm are presented here to show the improvement in spatial resolution in the ion and electron images. Simulated trajectory calculations show good agreement with experiment and ...

Velocity map imaging of ions and electrons using electrostatic lenses: Application in photoelectron and photofragment ion imaging of molecular oxygen

https://www.pci.uni-heidelberg.de/tc/usr/mctdh/lit/rev.pdf

The multiconfiguration time-dependent Hartree (MCTDH) method: a highly efficient algorithm for propagating wavepackets

In this article we present a new method for reconstructing three-dimensional (3D) images with cylindrical symmetry from their two-dimensional projections. The method is based on expanding the projection in a basis set of functions that are analytical projections of known well-behaved functions. The original 3D image can then be reconstructed as a linear combination of these well-behaved functions, which have a Gaussian-like shape, with the same expansion coefficients as the projection. In the process of finding the expansion coefficients, regularization is used to achieve a more reliable reconstruction of noisy projections. The method is efficient and computationally cheap and is particularly well suited for transforming projections obtained in photoion and photoelectron imaging experiments. It can be used for any image with cylindrical symmetry, requires minimal user’s input, and provides a reliable reconstruction in certain cases when the commonly used Fourier–Hankel Abel transform method fails.

Reconstruction of Abel-transformable images: The Gaussian basis-set expansion Abel transform method

There is a need for the preparation of enantiomerically pure compounds for various applications. An efficient approach to achieve this goal is asymmetric catalysis. The chiral catalyst is usually prepared from a chiral auxiliary, which itself is derived from a natural product or by resolution of a racemic precursor. The use of non-enantiopure chiral auxiliaries in asymmetric catalysis seems unattractive to preparative chemists, since the anticipated enantiomeric excess (ee) of the reaction product should be proportional to the ee value of the chiral auxiliary (linearity). In fact, some deviation from linearity may arise. Such nonlinear effects can be rich in mechanistic information and can be synthetically useful (asymmetric amplification). This Review documents the advances made during the last decade in the use of nonlinear effects in the area of organometallic and organic catalysis.

Nonlinear Effects in Asymmetric Catalysis

Ion Imaging of the Photodissociation of OCS Near 217 and 230 nm

Several reactions of the form A+HD→AD(H)+H(D) have been studied by a two laser experiment. One laser dissociates a molecule to form a reactive atom A and the second laser monitors the hydrogen atom products by laser induced fluorescence. When A is F(2P), O(1D), and S(1D), the H/D ratios are 0.66±0.10, 1.13±0.08, and 1.91±0.10, respectively. Muckerman and co‐workers have given qualitative arguments that abstraction reactions should have an H/D ratio less than one whereas insertion reactions should have H/D greater than one. Inasmuch as extensive previous experimental and theoretical work has shown that F(2P)+H2 procedes by abstraction whereas O(1D)+H2 and S(1D)+H2 proceed largely by insertion, the present results are consistent with the general qualitative conjecture.

Isotopic branching ratio for the reaction A+HD→AD(H)+H(D)

Kinetic analysis of the relationship between the reaction time and the yields of the product in the enantioselective addition of diisopropylzinc to pyrimidine-5-carbaldehyde using chiral pyrimidyl alkanol proves that the reaction is autocatalytic.

Evidence of asymmetric autocatalysis in the enantioselective addition of diisopropylzinc to pyrimidine-5-carbaldehyde using chiral pyrimidyl alkanol

The total cross sections for the reactions H + D/sub 2/ = HD + D and H + HD = H/sub 2/ + D have been measured as a function of relative initial translational energy in the ranges 0.87 to 2.70 and 0.82 to 1.86 eV, respectively. The technical for measuring the rate constant exploits the fact that the atomic product and reactant have very similar absorption wavelengths and that nearly monoenergetic hydrogen atoms can be generated by photodissociation of particular small molecules. Detection of the hydrogen atoms was carried out by laser-induced fluorescence at such short times that single collision conditions prevailed. The measured cross sections are in excellent agreement with the classical trajectory calculations of Blais and Truhlar and Schechter and Levine. As a byproduct of these experiments it was shown by Doppler spectroscopy that at the wavelengths 248 and 193 nm the transition dipole moment for H/sub 2/S is perpendicular to the molecular plane and that almost all of the available energy in this photodissociation is released into translation.

Isotopic variants of the atomic hydrogen + hydrogen reaction. 1. Total reaction cross sections of the atomic hydrogen + deuterium and atomic hydrogen + hydrogen deuteride reactions as a function of relative energy

Koichi Tsukiyama

Papers

Ion Imaging of the Photodissociation of OCS Near 217 and 230 nm

Isotopic branching ratio for the reaction A+HD→AD(H)+H(D)

Evidence of asymmetric autocatalysis in the enantioselective addition of diisopropylzinc to pyrimidine-5-carbaldehyde using chiral pyrimidyl alkanol

Isotopic variants of the atomic hydrogen + hydrogen reaction. 1. Total reaction cross sections of the atomic hydrogen + deuterium and atomic hydrogen + hydrogen deuteride reactions as a function of relative energy

Fluorescence lifetimes of no A2Σ+(ν′= 3 and 4), C2Π(ν′= 0) and D2Σ+(ν′= 0) studied by tunable VUV laser excitation