The effect of cross-flow velocity on mean-square derivatives measured using hot wires

 It is well known that significant errors occur in the velocity derivative moments measured in turbulent flows when the measuring transducer is too large or Taylor's hypothesis is used in high-turbulence-intensity flows. An additional error occurs when velocity derivative moments are measured with hot wires in high-turbulence-intensity flows, because the wires cannot resolve the individual velocity components in these flows. Estimates of the error this causes in the derivative moments measured with single-, cross-, and parallel-wire probes are developed herein. The errors are significant in the derivative moments measured with cross-wire probes, but are smaller in derivative moments measured with single- and parallel-wire probes. For example, the relative errors in measured in the far field of the round jet are 30–50% smaller than predicted in previous analyses. Received: 10 March 1995/Accepted: 07 December 1999     

First Higher‐Order Photocycloaddition to a CN Bond: 1,3‐Diazepines from Maleimides

A light touch is all that is required to cleave a maleimide C? N bond to effect a [5+2] photocycloaddition with a sterically encumbered C?N moiety (see scheme).

     

Selective sampling with direct ion mobility spectrometric detection for explosives analysis

This study investigates the potential and limitations of a field-deployable analytical approach that involves selective capture of explosive materials with direct analysis by ion mobility spectrometry (IMS). Selective capture of explosives was performed on deactivated quartz fiber filters impregnated with metal β-diketonate polymers. These Lewis acidic polymers selectively interact with Lewis base analytes such as explosives. The filters were directly inserted into an IMS instrument for analysis. The uptake kinetics of 2,4,6-trinitrotoluene (TNT) from a saturated atmosphere were characterized, and based on these studies, passive equilibrium sampling was applied to estimate the TNT concentration within an ammunition magazine that contained bulk TNT. Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) uptake from a saturated environment also was examined over a one-month period. Each incremental sampling period showed increasing quantities of RDX culminating with collection of approximately 5 ng of RDX on the filter at the end of one month. This is the first time that gas-phase uptake of RDX has been demonstrated.     

Electrochemical and alkali metal reduction studies of silicon,germanium, and tin derivatives of cyclooctatetraene : Properties conferred by cyclooctatetraenide dianions by group IV substituents

The electrochemical behavior of trimethylsilyl-, trimethylgermyl-, trimethylstannyl- and t-butylcyclooctatetraenes has been examined by the techniques of polarography and cyclic voltammetry in THF and hexamethylphosphoramide (vastly preferred) solutions. Chemical reduction by means of potassium in ND₃ has also been studied. Evidence is presented that all four compounds undergo reduction to their respective dianions. However, the energetics of (Me₃)MCOT^? and (Me₃)MCOT^2? formation vary widely, as do the rates and mechanism of dianion disappearance under the conditions of electrochemical measurement. The available kinetic data suggest, for example, that destruction of the t-Bu and trimethylgermyl substituted dianions proceeds via protonation and/or disproportionation pathways. In contrast, the silyl and stannyl examples experience metal-ring carbon cleavage reactions at yet faster rates. Interestingly, the E¹_{$\text{1}\text{2}$} values give evidence of being quite well correlated by σ_p. Furthermore, when the magnitude of the E¹_{$\text{1}\text{2}$}-E²_{$\text{1}\text{2}$} gap are plotted vs the covalent radii of the M atoms, a straight line is obtained for the Si, Ge and Sn examples; C deviates widely. This effect is believed to have its origin in resonance of the M←C_π type involving the d orbitals of M which, of course, is not possible in the carbon case. The significance of these results as well as the other observations made in the course of this work is discussed.     

Infrared spectroscopy of SO2 aqueous solutions

The chemistry of SO2 solutions was studied with infrared transmission and total internal reflection (ATR) spectroscopy. The cross-sections of the SO2 stretching vibrations v1, v3 and the combination band of v1 + v3 were obtained and found to be slightly different from their gas phase values. Six features we associate with sulfur-containing ions were observed. We present the first infrared evidence for the bisulfite ion HOSO2- through detection of its OH stretching vibration. Other features may be associated with HSO3-, another isomer of the bisulfite ion, and a new compound we propose to be H2S2O6(2-). We found no evidence for sulfurous acid H2SO3.     

On the structure of water—alcohol and ammonia—alcohol protonated clusters

Collision-induced dissociation (CID) of protonated ammonia-alcohol and water-alcohol heteroclusters was studied using a triple quadrupole mass spectrometer with a corona discharge atmospheric pressure ionization source. CID results suggested that the ammonia-alcohol clusters had NH: at the core of the cluster and that hydrogen-bonded alcohol molecules solvated this central ion. In contrast, CID results in water-alcohol clusters showed that water loss was strongly favored over alcohol loss and that there was a preference for the charge to reside on an alcohol molecule. The results also indicated that a loose chain of hydrogen-bonded molecules was formed in the water-alcohol clusters and that there appeared to be no rigid protonation site or a fixed central ion. (J Am Soc Mass     

Structures and properties of linear Cn molecules

Total energies, bond lengths, charge distributions, electronic configurations, and cohesive energies are calculated for linear C_n clusters, n = 2–6. The calculations are done at the single determinant Hartree-Fock level using both double-zeta and double-zeta plus polarization basis sets.