共查询到20条相似文献,搜索用时 15 毫秒
1.
A laser-induced fluorescence technique has been used to measure the rate of the energy-transfer reaction Ca(3P) + Sr(1S) α Ca(1S) + Sr(3P). Rates for quenching Sr(3P) by inert gases were also measured and correlated with an orbiting model. 相似文献
2.
Rate constants for collisional removal of ã1A1 and b?1B1 CH2 and CD2 have been directly measured, using IR laser induced multiple photon dissociation to prepare the radicals, and time resolved laser induced fluorescence to observe them. For CH2(ã1A1) removal by He, Ne, Ar, Kr, Xe, N2, H2, O2, CO and CH4, rate constants of 3.1, 4.2, 6.0, 7.0, 16, 8.8, 130, 30, 56 and 73 × 10?12 cm3 molecule?1 s?1 were found respectively. These represent significant increases over the previously accepted values. Essentially no isotope effect is observed in the removal of CD2(ã1A1) by the rare gases. The rate determining step in removal by the rare gases and N2 is thought to be singlet—triplet intersystem crossing controlled by long range attractive forces, and the results are discussed in terms of both isolated and mixed state theoretical models of these processes. For the other molecular collision partners, bimolecular chemical removal channels are possible, and may account for the relatively fast rates observed. Radiative lifetimes of five Σ vibronic levels of CH2(b?1B1) and three Σ vibronic levels of CD2(b?1B1) have been measured and found to lie in the range 2.5–6.0 μs, and collisional quenching rates for CH2(b?1B1) are found to be of the order of the gas kinetic collisional frequency. 相似文献
3.
Li2 molecules in a vapour cell were excited into the A 1Σ+u state using a dye laser set at 6103 Å. In the presence of a foreign gas Li(2 2P) atoms were detected by means of the Li(3 2D-2 2P) transition which was simultaneously excited by the 6103 Å radiation. From the pressure dependence of the normalized Li fluorescence intensity absolute rate constants for collision-induced dissociation Li2(A) → Li(2 2P) by the five rare gases were determined. The results are compared with recent work on the analogous process in the Li2(B 1Πu) state and with other systems. 相似文献
4.
High-energy protons and neutrons produce various radionuclides in the air, mainly through the nuclear spallation of atmospheric
elements. Air samples were collected from the EP-2 tunnel of the KEK 12 GeV proton synchrotron facility with a filter pack,
which consisted of a membrane filter for aerosols, a Na2CO3-impregnated filter for acidic gases, and an activated carbon fiber filter for non-acidic gases. Sulfur-38 was found on the
membrane and Na2CO3-impregnated filters, 38Cl and 39Cl were on the membrane, Na2CO3-impregnated, and ACF filters, and 82Br was only on the ACF filter. The results on the relative abundances of aerosol and gaseous acidic components have indicated
that 38Cl produced by thermal neutron capture, which is the main reaction for 38Cl production in the EP-2 tunnel air, are likely not to be present as aerosol or acidic gas. This was similar to the case
of 82Br produced by thermal neutron capture. 相似文献
5.
Infrared fluorescence observed after exciting to ν6 (ν=1) of CD3H with a Q-switched CO2 laser yields the exponential deactivation rate constant of 0.84 ms?1 torr?1. Rate constants for deactivation of CD3H by rare gases vary from 1.4 (for He) to 0.029 (for Xe) ms?1 torr?1. 相似文献
6.
The gas phase reactions of Ge(3P0,1) and Si(3PJ) with O2, NO and N2O have been studied in a flow tube system at 350 K. Atomic Ge and Si were produced by flowing GeH4 and SiH4 through a hollow cathode discharge. The subsequent disappearance of the Ge and Si atoms was followed with atomic absorption spectroscopy. Rate constants were determined for the reactions at 4 and 5 torr pressures. 相似文献
7.
Measurements of the Penning ionization cross section, σPI of D atoms by metastable He atoms show that σPI for the reaction He (2 1S) + D is much larger than σPI for He (2 3S) + D. In the relative velocity range νr = (2.3–4.8) × 105 cm/s (0.037–0.163 eV), σPI for He (2 1S) + D collisions was found to vary as νr?0.33. 相似文献
8.
Energy-transfer reactions between He(2 3S) and Ne(3P0.2) metastable atoms and PN radicals have been investigated by emission spectroscopy. Thirteen new PN+ (B 1Σ+ ?X 2Σ+) emission bands were found in addition to eight previously identified bands in the range 305–395 nm. From these observed band-head wavelengths, the following molecular constants were obtained for the X and B states of PN+ : PN+ (X): ωc = 1306 ± 3 cm?1, ωcxc = 7.9 ± 0.7 cm?1, PN? (B): Tc = 31354 ± 6 cm?1, ωc = 719 ± 3 cm?1, ωcxc = 1.6 ± 0.7 cm?1. The PN+ (B) state vibrational population was estimated from the emission intensities and the calculated Morse Franck—Condon (FC) factors for the PN+ (B–X) transition. Both the results obtained by He(2 3S) and Ne(3P0.2) Penning ionization shifted to lower vibrational levels in comparison with the calculated FC factors for vertical PN(X) → PN+ (B) ionization. Besides PN+ (B–X) emission, unidentified bands were observed in the 231–236 nm region in the helium afterglow, probably originating from PN or PN?. 相似文献
9.
Rudolf Knorr 《Tetrahedron》1981,37(5):929-938
Theoretical and experimental arguments are presented supporting the postulate that olefinic NMR coupling constants 2JHH are insensitive to β-substituent influences on the olefinic π orbital. A new set of substituent constants, σJI, is proposed to measure directly the inductive substituent effect transmitted by σ-bonds. The previously available range of inductive substituent constants can be appreciably extended in this way. Comparisons of σJI with other observables and parameters for selected substituents are made as a test of consistency. 相似文献
10.
The rate coefficient for deactivation of the metastable 23S state of He by impact of thermal electrons is deduced from recent calculations of inelastic electron-He cross sections. The deactivation rate is found to be nearly constant with temperature. Computed values range between 2.82 and 3.03 (10?9 cm3/sec) for T between 0 and 2000°K. De-excitation cross sections are given for low-energy incident electrons. 相似文献
11.
Rate constants and product distributions have been determined for the ion-molecule reactions between 12C+ and methane, ethane, propane, ethylene, propylene, allene, acetylene, propyne and benzene. The measurements were carried out with the SIFT technique at a temperature of 296 ± 2K. The results provide insight into the build-up of carbon skeletons to form C+n+1 ions and other competing modes of reaction at room temperature. 相似文献
12.
Sixteen new vibrational levels of 7LiD (X 1∑+) were found by analysis of laser-excited fluorescence spectra. They extend up to ν″ = 20, corresponding to 82% of the dissociation energy of LiD. New rotational and vibrational constants were derived from the data and were used for an RKR calculation of the 7LiD (X 1∑+) potential. Extra-polating this potential up to the dissociation limit gives agreement with the known dissociation energy to within 90 cm?1. 相似文献
13.
Zusammenfassung Ein Quencheffekt tritt auch nach Oxydation der organischen Probe auf. Dieser ist bedingt durch gewisse Verbrennungsprodukte, wie NO2, Halogene, SO2 und SO3. Es wurde gefunden, da\ man den Quencheffekt der Verbrennungsprodukte bei der Bestimmung von 14C und 35S ausschalten kann, wenn man die Spannung des Data-Photomultipliers bis zu einem gewissen Punkt (Kompensationspunkt) erhöht und die Messung in einem ZÄhlfenster durchführt. Der Kompensationspunkt wird graphisch ermittelt; hierzu mi\t man die ZÄhlrate des reinen Absorbens sowie die ZÄhlrate des Absorbens, das die maximal zu erwartende Menge Verbrennungsprodukt enthÄlt, bei verschiedenen Data-Spannungen. Der Zusammenhang zwischen der instrumenteilen Kompensation und dem Energiespektrum von 14C wird aufgezeigt. Bei der Bestimmung von Tritium lÄ\t sich der Quencheffekt nicht kompensieren, denn das Energiespektrum von Tritium wird durch eine Quenchverbindung anders beeinflu\t als das Spektrum von 14C bzw. 35S.
Summary After combustion of the organic sample a quenching effect is observed, due to several combustion products as NO2, halogens, SO2, and SO3. We found, that it is possible to eliminate quenching of the combustion products in the determination of 14C and 35S, if the high voltage of the data-photomultiplier is raised to a certain level (compensation point) and if the counting is performed in a window. The compensation point is calculated graphically by determining the counting rate of the pure absorbant and the absorbant plus the highest expected amount of combustion products. The relation between instrumental compensation and the energy spectrum of 14C is elucidated. It is not possible to compensate quenching in the determination of tritium, because the energy spectrum of 3H is influenced in a different way than the spectrum of 14C and 35S.相似文献
14.
Calculation of 1J(13C-29si) spin-spin coupling constants by the maximum overlap approximation method
The spin-spin 1J(C-Si) coupling constants were calculated by the maximum overlap approximation method for a series of related organosilicon compounds. It was concluded that the variation in hybridization of the relevant carbon atom accounts for the changes in 1J(C-Si) observed experimentally. 相似文献
15.
Analysis of new emission spectra of Ã2Σ+-X? 2Π in N2O+, including the forbidden components with Δν2 = 1, have made it possible to locate all four vibronic components of the ν″2 = 1 manifold. Principal rotational constants and spinvibronic terms are given. A previous estimate of the Renner parameter is revised to a value of ?0.179 ± 0.002. 相似文献
16.
1H, 13C and 29Si NMR data for the compounds (CH3)xSi(CH2CHCH2)4-x are reported. The 1H resonances from the π system are indicative of the electron-supplying inductive effect (+I) of the (CH3SiCH2, moiety but the corresponding 13Cπ chemical shifts seem to be influenced by a sterically induced polarization of the C-H bonds. The 13CAll, 13CMe and 29Si chemical shift data reveal an important neighbour anisotropy contribution originating from the π system. Ultraviolet study of the compounds mentioned above gives indication of a σ—π conjugation in accordance with PES and ab initio results [1—5]. The trend observed in the various coupling constants is too small to be Interpreted. 相似文献
17.
By application of a modified LAOCN-3 program a complete elucidation of the 1H NMR spectra of 2,3-unsaturated glycosyl phosphonates 1–5 could be achieved. The exactly determined nJ(H, H) and novel nJ(C, P) coupling constants are discussed, and permit a conclusive deduction of the conformations. The 13C NMR spectra of 1 to 6 can be fully interpreted. By a close inspection of chemical shifts as well as 1J(C-H) and nJ(C, P) coupling constants the conformational assignment is supported. For all the derivatives the correlations 1J(C-1,He)>1J(C-1, Ha) and 1J(C-1, Pe) >1J(C-1, Pa) can be used for the assignment of anomers. The crystal structure of 1 is in accordance with this assignment of anomers and displays an unexpected conformation. Calculations by MINDO-3 in resembling model compounds serve to elucidate such conformative effects. 相似文献
18.
Radioactive 2,4-dichlorophenyl methanesulfonate labeled with 14C and 35S has been synthesized because it was needed to facilitate the study of the metabolic fate of this interesting nematicide. It was prepared from the reaction between methanesulfonyl chloride and 2,4-dichlorophenol in the presence of a base. Three hundred milligrams of each 14C- and 35S-2,4-dichlorophenyl methanesulfonate was obtained in a yield of 87% based on 14C-2,4-dichlorophenol or 35S-methanesulfonyl chloride, respectively. The specific activity was 3.8 mCi/mmol for the compound labeled with 35S and 2.5 mCi/mmol for the 14C material. Both tracers assayed over 99% after purification. 相似文献
19.
Rate coefficients for collisional removal of O(1D) by six atmospheric gases have been measured by monitoring the appearance of O(3P) following photolytic production of O(1D). The measured values, kM±2σ, in units of 10?11 cm?3 molecule ?1 s?1 are kO3 = 22.8±2.3, kN2 = 2.52 ± 0.25, kCO2 = 10.4 ± 1.0,kH2O 195± 2.0, kN2O = 11.7 ± 1.2, and kH2, = 11.8±1.2. 相似文献
20.
Two radiometric methods for the determination of submugram amounts of cobalt are described. (A) Cobalt is extracted from an ammoniacal solution with a zinc-diethyldithiocarbamate-35S solution in chloroform. Excess reagent and interfering metals are removed with mercury(II) and cyanide. The 35S in the final organic layer is a measure of the cobalt in this layer. (B) Cobalt is extracted from an ammoniacal solution with a fixed amount of zinc-DDC in chloroform. Excess reagent and complexes of foreign metals are removed by exchange with 203Hg+2 and the 203Hg in the chloroform (compared with a blank) acts as a measure of the cobalt. Method A is applicable to 0.1 μg of cobalt and method B to 0.8 μg. As the efficiency of both processes is variable, isotope dilution with 60Co is carried out, A 10-fold excess of foreign metals is permitted in method A and a 4-fold excess in method B ; larger amounts are previously removed, e.g. by extraction with inactive zinc-DDC from sodium hydroxide media. 相似文献