Effects of target gas in collision-induced dissociation using a double quadrupole mass spectrometer and radiofrequency

Collision-induced dissociation (CID) of polyatomic ions sampled from an rf-powered glow discharge is examined by using three target gases including atomic (Ar and Xe) and molecular species (N2). Collisions with these targets in the first quadrupole of the double quadrupole system result in the loss of discharge species by dissociation, symmetric and asymmetric charge exchange, and scattering, each to varying degrees. These processes are seen to be a function of the relative mass, size... and ionization potentials of the target species, as well as the collision center-of-mass energies. In light of the comparisons, xenon appears to be the best collision target for both CID and charge exchange because of its relatively low ionization potential and high dissociation efficiency of polyatornic species. Evidence for both symmetric and asymmetric charge exchange is presented for Ar and Xe target gases.     

Direct generation of ion beam images with a two-dimensional charge injection device

The use of a two-dimensional charge injection device (CID) to directly image the spatial profile of impingent positively charged ions is described. By this approach, no prior conversion from an ion beam to a photon image is required. Because of the positive response of the device to plasma photons, ions that emanated from the radiofrequency glow discharge source were diverted around a photon stop and focused onto the CID. The resultant ion images were digitized via an external image processor and corrected for dark current contributions. Two-dimensional ion images and single pixel line profiles are presented.     

Preparative isolation of (+)-beta-eudesmol fromAmyris balsamifera

Summary Optically pure (+)-beta-eudesmol is a possible starting material for the synthesis of several termite defense compounds. A two step procedure for the isolation of gram quantities of (+)-beta-eudesmol from commercially availableAmyris balsamifera oil (syn. West Indian sandalwood oil), containing 8% beta-eudesmol, was developed. Step one consisted of an efficient vacuum distillation of the total oil. Step two was a medium pressure LC separation with an AgNO₃ impregnated silica gel stationary phase. Several other separation procedures failed due to the presence of many closely related sesquiterpene alcohols (75% of the oil).     

Green photoluminescence from platinum(II) complexes bearing silylacetylide ligands

The synthesis, structural characterization, photoluminescence properties, and density functional theory analysis of three Pt(II) diimine complexes, Pt(dbbpy)(C triple bond CR)2 [dbbpy = 4,4'-di(tert-butyl-2,2'-bipyridine; R = -SiMe3, -CC-SiMe3, or -t-Bu], are presented. The Pt(dbbpy)(C triple bond C-tBu)2 complex serves as a carbon-based ligand structure for which the photophysical properties of the two silicon-bearing complexes are compared in dichloromethane. Pt(dbbpy)(C triple bond C-SiMe3)2 and Pt(dbbpy)(C triple bond C-C triple bond C-SiMe3)2 display visible absorptions with strong green emission (lambda(emmax) = 526 and 524 nm, respectively) while Pt(dbbpy)(C triple bond C-t-Bu)2 displays efficient, long-lived yellow emission (lambda(emmax) = 557 nm). Direct side by side comparisons of Pt(dbbpy)(C triple bond C-SiMe3)2 and Pt(dbbpy)(C triple bond C-t-Bu)2 suggest that the difference in excited state energy results from the relative sigma-donor strength of the acetylide ligands.     

Mass spectrometry in structural and stereochemical problems—CLXXXIV: Charge localization in fragment ions of amino ketones and esters

The mass spectral fragmentation of a number of specially synthesized amino esters and ketones has been studied in which the distance between the two functionalities has been varied. The principal fragments formed following initial ionization are the even-electron immonium ions a and b. Further fragmentation of ion a in the amino esters occurs via non-specific processes. Therefore it is difficult to establish the degree of mobility of the positive charge in the fragment ions, notably whether the species with the charge present on the oxygen atom makes a significant contribution to the fragmentation. The β-(IIb) and γ-(IV) amino ketones show no McLafferty rearrangements after α-fission, thus demonstrating that uncoupling of the carbonyl π electrons is not a feasible trigger in lieu of charge localization.     

Microgravity flow regime data and analysis

To utilize the advantageous properties of two-phase flow in microgravity applications, the knowledge base of two-phase flow phenomena must be extended to include the effects of gravity. In the experiment described, data regarding the behavior of two-phase flow in a conduit under microgravity conditions (essentially zero gravity) are explored. Of particular interest, knowledge of the void fraction of the gas and liquid in a conduit is necessary to develop models for heat and mass transfer, pressure drop, and wall shear. An experiment was conducted under reduced gravity conditions to collect data by means of a capacitance void fraction sensor and high speed visual imagery. Independent parameters were varied to map the flow regime regions. These independent parameters include gas and liquid volumetric flow rates and saturation pressures. Void fraction measurements were taken at a rate of 100 Hz with six sensors at two locations along the conduit. Further, statistical parameters were developed from the void fraction measurements. Statistical parameters such as variance, signal-to-noise ratio, half height value, and linear area difference were calculated and found to have characteristics allowing flow regime identification.     

Quantitative model studies of stirrers for laboratory glass melts

The stirrers widely used in practice are investigated and compared in the present work using the method of quantitative assessment of homogeneity.     

中心下陷的负色散光纤

利用非等温等离子体化学气相沉积成功制得了具有折射率中心下陷的负色散光纤 (RDF)。该光纤在保持较好的抗弯曲性能与偏振模色散的同时 ,有效面积达到 4 5 μm2 ,且在 15 5 0nm处的色散为 - 19.6 5ps/(nm·km) ,色散斜率为 - 0 .132ps/(nm2 ·km)。此外 ,通过优化光纤纤芯各层的掺杂原子浓度 ,在 15 30nm处光纤的氢损降到了0 .0 1dB/km。由负色散光纤与具有超大有效面积的非零色散位移光纤 (ULAF)组成的色散管理光纤对在 15 30nm到16 2 5nm波长范围内的色散斜率小于 0 .0 0 6ps/(nm2 ·km) ,且最大色散值小于 0 .2ps/(nm·km)。同时 ,15 5 0nm波长处的衰耗为 0 .2 2 4dB/km ,且在 15 30nm到 16 2 5nm波段范围内衰耗较为平坦。该色散管理光纤对可以在无需色散补偿模块的前提下应用于大容量高速率的长距离波分复用 (WDM)系统。