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91.
Convexity properties of the moment mapping 总被引:10,自引:0,他引:10
92.
Møllendal H Demaison J Petitprez D Wlodarczak G Guillemin JC 《The journal of physical chemistry. A》2005,109(1):115-121
1,2-Propadienylphosphine (allenylphosphine), H(2)C=C=CHPH(2), has been investigated by Stark and Fourier transform microwave spectroscopy. Two rotameric forms denoted syn and gauche have been assigned. The syn form has a symmetry plane (C(s)() symmetry) where the lone electron pair of phosphorus points toward the double bonds. The phosphino group is rotated roughly 120 degrees from this position in the gauche rotamer. The dipole moment of syn was determined to be mu(a) = 1.613(23), mu(b) = 2.347(24), mu(c) = 0 (for symmetry reasons), and mu(tot) = 2.848(28) x 10(-30) C m [0.854(8) D]. The energy difference between the two forms was found to be 2.1(4) kJ/mol from relative intensity measurements with syn as the more stable conformer. Extensive quantum chemical calculations have been carried out and accurate equilibrium structures have been determined for these two rotamers, as well as for the corresponding two conformers of vinylphosphine (H(2)C=CHPH(2)). 相似文献
93.
Piancastelli MN Stolte WC Guillemin R Wolska A Lindle DW 《The Journal of chemical physics》2008,128(13):134309
We have studied the fragmentation dynamics of core-excited SiF4 by means of soft-x-ray photoexcitation and partial positive and negative ion yield measurements around the Si L2,3-shell and F K-shell ionization thresholds. All detectable ionic fragments are reported and we observe significant differences between the various partial ion yields near the Si 2p threshold. The differences are similar to our previous results from CH3Cl showing more extended fragmentation in correspondence to transitions to Rydberg states. At variance with smaller systems, we observe negative ion production in the shape resonance region. This can be related to the possibility in a relatively large system to dissipate positive charge over several channels. 相似文献
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96.
Céolin D Miron C Le Guen K Guillemin R Morin P Shigemasa E Millié P Ahmad M Lablanquie P Penent F Simon M 《The Journal of chemical physics》2005,123(23):234303
X-ray photoelectron spectroscopy and Auger spectroscopy studies of gas-phase hexamethyldisiloxane (HMDSO) are presented. The photodissociation of this molecule is studied using various experimental coincidence techniques. We compare the fragmentation pathways observed after core ionization followed by Auger decay and after valence double photoionization of the molecule. A strongly selective production of the doubly charged tetramethyldisiloxane ion is observed in the low binding-energy regions. Theoretical calculations are carried out to tentatively explain the stability of the produced dication. 相似文献
97.
C. L. Guillemin 《Journal of separation science》1980,3(12):620-626
Three main problems have to be solved in process gas chromatography: psychological, technical and economic. A simple concept already used with success for fifteen years by the author, called the Deferred Standard, is an answer for process GC and, to some extent, laboratory GC as well. That the injection of a pure compound in each analytical sequence is reproducible demonstrates the good working order of PGC. Accurate quantitative results may be obtained because the gas density balance is used as a calibrator detector for determining the relative response factors of the components of interest with respect to the Deferred Standard. By suppressing any calibration standards in process and laboratory chromatography, the Deferred Standard may reveal itself as a time and money saving technique. 相似文献
98.
99.
Fr. Shindo Y. Bnilan P. Chaquin J.-C. Guillemin A. Jolly Fr. Raulin 《Journal of Molecular Spectroscopy》2001,210(2):191
Polyynes are of astrophysical interest since they appear to be involved in organic chemistry in very different mediums. In Titan's atmosphere, the lightest polyyne, C4H2, was detected by Voyager. Recently C4H2 and C6H2 have been discovered in a protoplanetary nebula, suggesting polyynes as a possible chemical pathway to PAH (polycyclic aromatic hydrocarbons). Moreover, several experimental simulations and modeling imply their production from the photochemistry of methane and their involvement in the formation of organic aerosols. After the study of C4H2 and C6H2 spectra in the UV and IR wavelength range, we report here the first spectrum of gaseous C8H2 in the range 400–4000 cm−1 at room temperature and low resolution. The task was hardly achieved because of the high instability of this molecule with temperature and pressure. To avoid exothermic polymerization, the compound as mixed with a solvent. We have performed a separate spectroscopic study of the solvent to determine C8H2 partial pressure within the mixture. This allowed us to calculate C8H2 integrated band intensities. In the studied wavelength range, C8H2 presents three main bands similar to those of C6H2 in terms of vibrational type, position, and relative intensity. To study the possible identification of these polyynes by spatial observatories (Cassini–Huygens, ISO), we have also measured the C6H2 and C8H2 infrared spectra in the range 400–1500 cm−1 at 0.35 cm−1 resolution. 相似文献
100.
We analyze the so-called shortest queue first (SQF) queueing discipline whereby a unique server addresses queues in parallel by serving at any time, the queue with the smallest workload. Considering a stationary system composed of two parallel queues and assuming Poisson arrivals and general service time distributions, we first establish the functional equations satisfied by the Laplace transforms of the workloads in each queue. We further specialize these equations to the so-called “symmetric case,” with same arrival rates and identical exponential service time distributions at each queue; we then obtain a functional equation $$\begin{aligned} M(z) = q(z) \cdot M \circ h(z) + L(z) \end{aligned}$$ for unknown function M, where given functions \(q, L\) , and \(h\) are related to one branch of a cubic polynomial equation. We study the analyticity domain of function M and express it by a series expansion involving all iterates of function \(h\) . This allows us to determine empty queue probabilities along with the tail of the workload distribution in each queue. This tail appears to be identical to that of the head-of-line preemptive priority system, which is the key feature desired for the SQF discipline. 相似文献