CSRe储存环动力学孔径研究(英文)；Dynamic Aperture Studies for CSRe Storage Ring

动力学孔径对环形加速器,尤其是现代的储存环,起着越来越重要的作用。采用MAD程序研究了兰州重离子加速器实验环(CSRe)的动力学孔径。通过对比几种情况下的模拟结果,发现六极铁和二极铁的高阶场对束流的动力学孔径影响较大,使CSRe的动力学孔径减小,但减小后的动力学孔径也远大于该环的物理孔径。因此,束流可以长期、稳定的存在。

An integrating current transformer for fast extraction from the HIRFL-CSR main ring

For any experiment that uses the beam of an accelerator, monitoring the beam intensity is always art important concern. It is particularly useful if one can continuously measure the beam current without disturbing the beam. We report here on test experiments for an Integrating Current Transformer (ICT) used to measure fast extraction beams from the HIRFL-CSR main ring (CSRm). The laboratory tests and beam intensity measurement results are presented in this paper. The influence of the kicker noise is also analyzed.

Dissociative recombination of the acetaldehyde cation, CH3CHO+

The dissociative recombination of the acetaldehyde cation, CH3CHO+, has been investigated at the heavy ion storage ring CRYRING at the Manne Siegbahn Laboratory in Stockholm, Sweden. The dependence of the absolute cross section of the reaction on the relative kinetic energy has been determined and a thermal rate coefficient of k(T) = (1.5 +/- 0.2) x 10(-6) (T/300)(-0.70 +/- 0.02) cm(3) s(-1) has been deduced, which is valid for electron temperatures between similar to 10 and 1000 K. The branching fractions of the reaction were studied at similar to 0 eV relative kinetic energy and we found that breaking one of the bonds between two of the heavy atoms occurs in 72 +/- 2% of the reactions. In the remaining events the three heavy atoms stay in the same product fragment. While the branching fractions are fairly similar to the results from an earlier investigation into the dissociative recombination of the fully deuterated acetaldehyde cation, CD3CDO+, the thermal rate coefficient is somewhat larger for CH3CHO+. Astrochemical implications of the results are discussed.

PROJECTILE FRAGMENTATION OF Ar-36,Ar-40 INDUCED REACTIONS

Fragment yields for Z >= 5 from projectile fragmentation using primary beams of Ar-36,Ar-40 at 50 MeV/nucleon on Ni-64 target have been measured in RIBLL fragment separator. We compare the fragment cross sections with the predictions of the empirical EPAX parametrization of fragmentation cross-sections and Statistical Abration-Ablation model (SAA) by considering the RIBLL separator transmission rate. Isotope yield ratios between these two reactions were calculated and isoscaling parameters alpha and beta are extracted, their dependences on fragment atomic number Z and neutron number N were presented.

DISSOCIATIVE RECOMBINATION OF PROTONATED PROPIONITRILE, CH3CH2CNH+: IMPLICATIONS FOR TITAN'S UPPER ATMOSPHERE

The dissociative recombination of protonated propionitrile, CH3CH2CNH+, has been investigated at the heavy ion storage ring, CRYRING, at the Manne Siegbahn Laboratory, Stockholm University, Sweden. The thermal rate coefficient has been deduced to follow k(T) = (1.5 +/- 0.2) x 10(-6) (T/300)(-0.76) (+/-) (0.02) cm(3) s(-1) for electron temperatures ranging from similar to 10 to similar to 1000 K. Measurements of the branching fractions were performed at similar to 0 eV relative kinetic energy. It has been found that in 43% +/- 2% of the reactions the four heavy atoms remain in the same product fragment. An equal portion of the reactions leads to products where one of the heavy atoms is split off from the other three and 14% +/- 1% result in a breakup into two heavy fragments containing two heavy atoms each. We discuss the significance of the data to Titan's upper atmosphere.

Experimental studies of the dissociative recombination of CD3CDOD+ and CH3CH2OH2+

Aims. We determine branching fractions, cross sections and thermal rate constants for the dissociative recombination of CD3CDOD+ and CH3CH2OH2+ at the low relative kinetic energies encountered in the interstellar medium. Methods. The experiments were carried out by merging an ion and electron beam at the heavy ion storage ring CRYRING, Stockholm, Sweden. Results. Break-up of the CCO structure into three heavy fragments is not found for either of the ions. Instead the CCO structure is retained in 23 +/- 3% of the DR reactions of CD3CDOD+ and 7 +/- 3% in the DR of CH3CH2OH2+, whereas rupture into two heavy fragments occurs in 77 +/- 3% and 93 +/- 3% of the DR events of the respective ions. The measured cross sections were fitted between 1-200 meV yielding the following thermal rate constants and cross-section dependencies on the relative kinetic energy: sigma(E-cm[eV]) = 1.7 +/- 0.3 x 10(-15)(Ecm[eV])(-1.23 +/- 0.02) cm(2) and k(T) = 1.9 +/- 0.4 x 10(-6)(T/300)-0.73 +/- 0.02 cm(3) s(-1) for CH3CH2OH2+ as well as k(T) = 1.1 +/- 0.4 x 10(-6)(T/300)(-0.74 +/- 0.05) cm(3) s(-1) and s(Ecm[eV]) = 9.2 +/- 4 x 10(-16)(Ecm[eV])-1.24 +/- 0.05 cm(2) for CD3CDOD+

N-arylamides from selenium-catalyzed reactions of nitroaromatics and amides in the presence of carbon monoxide and mixed organic bases

N-Arylamides were exclusively obtained in moderate to good yields from selenium-catalyzed reactions of nitroaromatics with amides in the presence of CO and mixed organic bases Et3N and DBU.

State-to-state dynamics of elementary chemical reactions using Rydberg H-atom translational spectroscopy

In this review, a few examples of state-to-state dynamics studies of both unimolecular and bimolecular reactions using the H-atom Rydberg tagging TOF technique were presented. From the H2O photodissociation at 157 nm, a direction dissociation example is provided, while photodissociation of H2O at 121.6 has provided an excellent dynamical case of complicated, yet direct dissociation process through conical intersections. The studies of the O(D-1) + H-2 --> OH+H reaction has also been reviewed here. A prototype example of state-to-state dynamics of pure insertion chemical reaction is provided. Effect of the reagent rotational excitation and the isotope effect on the dynamics of this reaction have also been investigated. The detailed mechanism for abstraction channel in this reaction has also been closely studied. The experimental investigations of the simplest chemical reaction, the H-3 system, have also been described here. Through extensive collaborations between theory and experiment, the mechanism for forward scattering product at high collision energies for the H+HD reaction was clarified, which is attributed to a slow down mechanism on the top of a quantized barrier transition state. Oscillations in the product quantum state resolved different cross sections have also been observed in the H+D-2 reaction, and were attributed to the interference of adiabatic transition state pathways from detailed theoretical analysis. The results reviewed here clearly show the significant advances we have made in the studies of the state-to-state molecular reaction dynamics.

In situ IR spectroscopic studies on molybdenum nitride catalysts: active sites and surface reactions

Recent IR spectroscopic studies on the surface properties of fresh Mo2N/gamma-Al2O3 catalyst are presented in this paper. The surface sites of fresh Mo2N/gamma-Al2O3, both Modelta+ (0<δ<2) and N sites, are probed by CO adsorption. Two characteristic IR bands were observed at 2045 and 2200 cm(-1), due to linearly adsorbed CO on Mo and N sites, respectively. The surface N sites are highly reactive and can react with adsorbed CO to form NCO species. Unlike adsorbed CO on reduced passivated one, the adsorbed CO on fresh Mo2N/gamma-Al2O3 behaves similarly to that of group VIII metals, suggesting that fresh nitride resembles noble metals. It is found that the surface of Mo nitrides slowly transformed into sulfide under hydrotreating conditions, which could be the main reason for the activity drop of molybdenum nitride catalysts in the presence of sulfur-containing species. Some surface reactions, such as selective hydrogenation of 1,3-butadiene, isomerization of 1-butene, and hydrodesulfurization of thiophene, were studied on both fresh and reduced passivated Mo2N/gammaAl(2)O(3) catalysts using IR spectroscopy. The mechanisms of these reactions are proposed. The adsorption and reaction behaviors of these molecules on fresh molybdenum nitride also resemble those on noble metals, manifesting the unique properties of fresh molybdenum nitride catalysts. Mo and N sites are found to play different roles in the adsorption and catalytic reactions on the fresh Mo2N/gammaAl(2)O(3) catalyst. Generally, Mo sites are the main active sites for the adsorption and reactions of adsorbates; N sites are not directly involved in catalytic reactions but they modify the electronic properties of Mo sites.