Transverse momenta of high-η charged particles emitted in Au+Au collisions

This work demonstrates that the mean transverse momentum of charged particles at large pseudo-rapidities can be reliably derived from measurements of the complete charged-particle multiplicity distributions and using information from measurements of p _T spectra at mid-rapidity by applying energy conservation requirements. As an example, the mean p _T of charged particles emitted at η=4.6 is found to be 〈p _T 〉=0.305 GeV/c for the 0–3% most central Au+Au collisions at $\sqrt {s_{NN} } = 130$ GeV.     

Strength function for fission in the two humped barrier model

The strength function model developed by Bohr and Mottelson is generalized to a system with two classes of states as encountered in the actinide region. Expressions for the distribution of vibrational strength amongst the compound states are derived under simplifying assumptions, and the effect on the fission decay is investigated.     

Effects of pi* <-- n Excitation in 4-Cyclopentene-1,3-Dione

The weak visible absorption spectrum of 4-cyclopentene-1,3-dione has been photographed near room temperature and assigned to the A(1)B(1) <-- X(1)A(1), pi* <-- n transition with origin at 22 000 cm(-1). A few weak bands near 28 465 cm(-1) have been assigned to a second (1)A(2) pi* <-- n transition. The effects of excitation are delocalized over the highly conjugated molecule, the most important geometrical change upon excitation being an in-plane distortion of the five-membered ring. Many sequences are observed in the ring-puckering and twisting modes, both of which increase substantially in wavenumber upon excitation. Possible reasons for this dramatic increase in the forces favoring ring planarity are discussed. Copyright 2000 Academic Press.     

Charged-particle multiplicity near midrapidity in central Au+Au collisions at sqrt[SNN]=56 and 130 GeV

We present the first measurement of pseudorapidity densities of primary charged particles near midrapidity in Au+Au collisions at sqrt[s(NN)] = 56 and 130 GeV. For the most central collisions, we find the charged-particle pseudorapidity density to be dN/deta|(|eta|<1) = 408+/-12(stat)+/-30(syst) at 56 GeV and 555+/-12(stat)+/-35(syst) at 130 GeV, values that are higher than any previously observed in nuclear collisions. Compared to proton-antiproton collisions, our data show an increase in the pseudorapidity density per participant by more than 40% at the higher energy.     

The cycloaddition of ethylene to butene-2. I. Stereochemistry of the reaction

The rate of the thermal cycloaddition of ethylene to cis and trans butene-2 has been measured at 693°K and at pressures of about 12 atmospheres. The ratio of trans- to cis-1,2-dimethylcyclobutane from the reaction of trans-butene-2 with ethylene was 5.1, obtained from the initial rates of formation of the products. Similarly, the ratio of cis- to trans-1,2-dimethyl-cyclobutane from the reaction of cis-butene-2 with ethylene was 2.8. The results show that the cycloaddition reactions are the reverse of the decomposition reactions of the dimethyl-cyclobutanes and may be interpreted in terms of a biradical intermediate. Several ratios of rate constants have been measured as well as the rate constants for the reaction of the olefins to form the intermediate biradical.     

The thermal decomposition of diimide in the gas phase: Kinetics and stoichiometry

The kinetics and stoiehiometry of the decomposition of N₂H₂ and N₂D₂ have been studied as a function of sample size, pressure, and temperature. The reaction follows a single first order kinetic expression over most of its time course. It is suggested that the rate-determining step in the mechanism is a first-order homogeneous gas-phase isomerization of trans-diimide with rate constants:k = 1.8 exp (-4.2 kcal/mol/RT) sec^?1 and k = 1 exp (-4.4 kcal/mol/RT) sec^?1. The detailed mechanism of this isomerization, however, is not evident. At temperatures above room temperature, self-heating has been observed which leads to an initial fast decay. At room temperature the reaction exhibits autocatalysis with the rate increasing as the reaction proceeds. This has been attributed to enhancement by a surface decay process involving adsorbed hydrazine. The only significant products from the decomposition of N₂H₂ are N₂, H₂, and N₂H₄, and the results are interpreted in terms of two parallel reactions: The decomposition of N₂D₂ occurs almost completely by the single reaction giving N₂ + N₂D₄. No azide formation has been detected from either N₂D₂, or N₂D₂, and limits have been put on the yield of ammonia. Extinction coefficients at 365 nm of 3.9 ± 0.2 for N₂H₂ and 3.3 ± 0.1 for N₂D₂ have been measured. Both the rate of decay and the stoichiometry of products show pressure dependence below 150 torr, and this is suggested to be due to direct decomposition of cis-N₂H₂ on the surface.     

Significance of the fragmentation region in ultrarelativistic heavy-ion collisions

We present measurements of the pseudorapidity distribution of primary charged particles produced in Au+Au collisions at three energies, sqrt[s(NN)]=19.6, 130, and 200 GeV, for a range of collision centrali-ties. The distribution narrows for more central collisions and excess particles are produced at high pseudorapidity in peripheral collisions. For a given centrality, however, the distributions are found to scale with energy according to the "limiting fragmentation" hypothesis. The universal fragmentation region described by this scaling grows in pseudorapidity with increasing collision energy, extending well away from the beam rapidity and covering more than half of the pseudorapidity range over which particles are produced. This approach to a universal limiting curve appears to be a dominant feature of the pseudorapidity distribution and therefore of the total particle production in these collisions.     

Kinetics of the bimolecular initiation process in the thermal reactions of ethylene

The initial rates of formation of the major products in the thermal reactions of ethylene at temperatures in the neighborhood of 750 K have been measured in the presence and absence of the additive butene-1. It has been shown that this ratio of rates is related to the ratio of rate constants for the two initiation processes: The ratio k′₁/k₁ has been measured over the temperature range of 700–773 K and may be expressed as (R = 1.987 cal/mol deg) log k′₁k₁(mol/L) = 2.8 ? 4400/2.3RT. Assuming a value for k′₁ of log k′₁ (s^?1) = 16 ? 71,500/2.3RT, the value of k₁ may be expressed as log k₁(L/mol) = 13.2 ? 67,000/2.3RT. The values for the frequency factor and activation energy for reaction (1) are discussed in relation to the heat of formation of the vinyl radical, and it is concluded that reaction (1) is the main initiation process in the thermal decomposition of ethylene under the present conditions.     

A convenient synthesis of selenolsulfonates from the oxidation of sulfonhydrazides with benzeneseleninic acid

The reaction of sulfonhydrazides with benzeneseleninic acid furnishes selenolsulfonates in high yield.