共查询到20条相似文献,搜索用时 31 毫秒
1.
Z. J. Jabbour K. E. Martus K. Becker 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1988,9(3):263-264
We measured the absolute photo-emission cross section of the BC ? A → X system around 2720 Å produced by electron-impact dissociation of BC?3. The cross section reaches a maximum around 40 eV with a value of 2.5±0.5 × 10?18 cm2. A double-onset structure with onsets around 14 eV and 26 eV indicates that the excited BC? fragments are produced via two different dissociation channels. 相似文献
2.
Dissociative electron attachment cross-section measurements for the production of O? from CO2 have been performed utilizing a crossed target-beam—electron-beam collision geometry and a quadrupole mass spectrometer. The relative flow technique is employed to determine the absolute values of cross sections. The attachment energies corresponding to the five cross-section maxima are: 4.4 ± 0.1, 8.2 ± 0.1, 13.0 ± 0.2, 16.9 ± 0.2 and 19.4 ± 0.2 eV. The cross sections at these maxima are: 1.43 × 10?19 cm2, 4.48 × 10?19 cm2, 8.1 × 10?21 cm2, 8.1 × 10?21 cm2 and 1.2 × 10?20 cm2, respectively. 相似文献
3.
Harold F. Winters 《Chemical physics》1979,36(3):353-364
The absolute total dissociation cross section for ethane is reported for electron energies between 10 and 600 eV. A maximum value of 7.6 × 10?16 cm2 occurs at 80 eV while the apparent threshold is ≈ 10 eV. Dissociative ionization is more probable than dissociation into neutral fragments at all energies except in the threshold region. The data indicates that fragmentation involving methane elimination (c? + C2 H6 → e? + CH4 + CH2) occurs in less than 2% of the dissociative events for 50 < E < 600 eV. Arguments are presented which suggest that some of the lower excited states of ethane are stable against dissociation. 相似文献
4.
The absolute total ionization cross sections from threshold to 250 eV and dissociative attachment cross sections from zero to 10 eV have been measured for the CCl2F2 (dichloro-difluoro-methane) molecule by using a parallel plate condenser type ionization chamber. The maximum of the ionization cross-section curve was found to be at an energy of about 90 eV with a cross section of 1.44 × 10?19 m2. The attachment cross-section curve shows three peaks, the most intense being at zero electron energy with a cross-section value of 1.80 × 10?20 m2, and the other two at energies of 0.6 eV and 3.5 eV, respectively. The maximal relative error in cross-section values is 0.08, for electron energies larger than 0.4 eV. 相似文献
5.
Jeffrey W. Keister Päivi Tomperi Tomas Baer 《Journal of the American Society for Mass Spectrometry》1998,9(6):597-605
The dissociation behavior of energy-selected tetraethylsilane, triethylsilane, and diethylsilane photocations is studied using the threshold photoelectron-photoion coincidence (TPEPICO) technique. In the 8–12. 5 eV photon energy range, 0 K dissociation onsets have been measured from the TPEPICO data. The dissociation channels observed include loss of ethane, hydrogen molecule, ethyl radical and hydrogen atom, depending upon the molecular ion under investigation. The thermochemistry of the molecular ions and dissociation fragments is obtained by an analysis that takes into account the kinetics and internal energy distributions of the ions. The various dissociation onsets permit the reevaluation of both neutral and ionic silane thermochemistry. We observed 298-K ethyl group values of 60±10 and 94±10 kJ mol?1 for neutral and ionic silanes, respectively. These values are considerably smaller than the previously reported values of 86 and 130 kJ mol?1, respectively. Finally, a Δ f H ° (298 K) of ?141.5 ± 21 kJ/mol for neutral diethyl silane is derived from the dissociative ionization onset of diethylsilane. 相似文献
6.
Masashi Uematsu Hisato Hiraishi Tsutomu Fukuyama Tamotsu Kondow Kozo Kuchitsu 《Chemical physics》1982,64(3):381-387
When benzene, acetylene and ethylene were allowed to collide with Ne Rydberg atoms (17?n?40), significant Ne+ ions were observed. Their cross sections were estimated, with reference to the ionization by H2O, to be as large as 10?14–10?15 cm2. However, no Ne+ signals were observed when ethane, methane and N2 were used as targets. Theoretical estimates of the cross sections for ionization by interaction of the quadrupole moment and polarizability of the first three molecules are several orders of magnitude smaller than the experimental cross sections given above. A similarity of this phenomenon to the scattering of a thermal electron by benzene etc., observed by Christophorou et al., is suggested. 相似文献
7.
We report new measurements of the absolute electron-impact double ionization cross sections for Ar and Kr and of the ratios of double-to-single ionization for impact energies from threshold to 200 eV using the crossed electron-beam — fast-atom-beam technique. The work was motivated by the recently highlighted spread of about 30% in the Ar2+/Ar+ ionization cross section ratios obtained by several groups using different experimental techniques. Such a spread is inconsistent with statistical uncertainties of typically 3% or less that were quoted for the various reported ratios. A similar situation exists for Kr where the spread among the recently published Kr2+/Kr+ ionization cross section ratios is about 15%. We made an attempt to identify all potential systematic errors inherent to the fast-beam technique that could affect the measurement of cross section ratios with special emphasis on those systematic errors that could influence the detection of singly and doubly charged product ions differently. We found Ar2+/Ar+ and Kr2+/Kr+ cross section ratios of, respectively 0.066 ±0.007 and 0.087 ±0.008 at 100 eV which confirm earlier measurements using the same experimental technique. The error limits on cross sections ratios measured in our fast-beam apparatus were determined to be at least ±9% for cross section ratios of multiple-to-single ionization for the same target atom and at least ±10% for ratios of single ionization cross sections for different target species. Our error limits are dominated by systematic uncertainties of the apparatus which do not cancel when cross section ratios are measured, since the ratios are obtained under similar, but not identical experimental conditions. 相似文献
8.
The relative rate technique has been used to measure rate constants for the reaction of chlorine atoms with nitro methane, nitro ethane, nitro propane, nitro butane, nitro pentane, ethyl nitrate, isopropyl nitrate, n-propyl nitrate, 2-pentyl nitrate, and 2-heptyl nitrate. Decay rates of these organic species were measured relative to one or more of the following reference compounds; n-butane, ethane, chloroethane, and methane. Using rate constants of 2.25 × 10?10 5.7 × 10?11, 8.04 × 10?12, and 1.0 × 10?13 cm3 molecule?1 s?1 for the reaction of Cl atoms with n-butane, ethane, chloroethane, and methane, respectively, the following rate constants were derived, in units of cm3 molecule?1 s?1: nitro methane, <7 × 10?15; nitro ethane, (2.05 ± 0.14) × 10?13; nitro propane, (1.13 ± 0.05) × 10?11; nitro butane, (5.13 ± 0.68) × 10?11; nitro pentane, (1.40 ± 0.14) × 10?10; ethyl nitrate, (3.70 ± 0.24) × 10?12; n-propyl nitrate, (2.15 ± 0.13) × 10?11; i-propyl nitrate, (3.94 ± 0.48) × 10?12; 2-pentyl nitrate, (1.00 ± 0.06) × 10?10; and 2-heptyl nitrate, (2.84 ± 0.50) × 10?10. Quoted errors represent 2σ and do not include possible systematic errors due to errors in the reference rate constants. Experiments were performed at 295 ± 2 K and atmospheric pressure (?740 torr) of synthetic air. The results are discussed with respect to the previous literature data and to the modeling of these compounds in the atmosphere. 相似文献
9.
SiH free radicals in a dc multipole post-discharge plasma were analyzed using laser-induced fluorescence. The cross section for SiH formation from 40–70 eV electron impact induced dissociation of SiH4 was measured to be (10 ± 5) × 10?17 cm2. At the instant of its formation in its X2Π ground state, the rotational temperature of the SiH radical is 950 K. This temperature subsequently relaxes by collisions with SiH at a collisional relaxation rate k = (9 ± 2) × 1013 cm3/mole s. Quenching of the A2Δ electronic state of SiH was found to be negligible below 0.3 Torr. The primary reaction path for destruction of the SiH radical was observed to be via: SiH + SiH4 → products, k = 2 × 1012 cm3/mole s. 相似文献
10.
The rate of the gas phase reaction of hydroxyl radical with methyl nitrate has been measured to be (3.4 ± 0.4) × 10?14 cm3 molecule?1 s?1 at 298 K using flow discharge/ resonance fluorescence techniques. By means of correlation methods, this rate determination is used to predict a vertical ionization potential of 12.6 eV, a bond dissociation energy for H? CH2ONO2 of 101 kcal mol?1, and a rate for O(3P) reaction with methyl nitrate of ca. 9 × 10?17 cm3 molecule?1 s?1. In conjunction with previously derived relative data for reaction of alkyl nitrates with OH radical in the gas phase, a priori estimated reactivities for 1-, 2-, and 3-positionally substituted straight chain alkyl nitrates have been reexamined. Revised reactivities for OH abstraction of specific hydrogens substituted on straight chain alkyl nitrates are presented and discussed, and an atmospheric lifetime of ca. 2 yrs is estimated for methyl nitrate removal due to OH. 相似文献
11.
Jens Sehested 《国际化学动力学杂志》1994,26(10):1023-1039
The ultraviolet absorption spectrum of CF3CFClO2 and the kinetics of the self reactions of CF3CFCl and CF3CFClO2 radicals and the reactions of CF3CFClO2 with NO and NO2 have been studied in the gas phase at 295 K by pulse radiolysis/transient UV absorption spectroscopy. The UV absorption cross section of CF3CFCl radicals was measured to be (1.78 ± 0.22) × 10?18 cm2 molecule?1 at 220 nm. The UV spectrum of CF3CFClO2 radicals was quantified from 220 nm to 290 nm. The absorption cross section at 250 nm was determined to be (1.67 ± 0.21) × 10?18 cm2 molecule?1. The rate constants for the self reactions of CF3CFCl and CF3CFClO2 radicals were (2.6 ± 0.4) × 10?12 cm3 molecule?1 s?1 and (2.6 ± 0.5) × 10?12 cm3 molecule?1 s?1, respectively. The reactivity of CF3CFClO2 radicals towards NO and NO2 was determined to (1.5 ± 0.6) × 10?11 cm3 molecule?1 s?1 and (5.9 ± 0.5) × 10?12 cm3 molecule?1 s?1, respectively. Finally, the rate constant for the reaction of F atoms with CF3CFClH was determined to (8 ± 2) × 10?13 cm3 molecule?1 s?1. Results are discussed in the context of the atmospheric chemistry of HCFC-124, CF3CFClH. © 1994 John Wiley & Sons, Inc. 相似文献
12.
Spectrally resolved collision-free absolute fluorescence cross sections have been measured, for NO2 excited, by the second harmonic of the Nd: YAG laser. The total cross section into the 523.0–650.0 nm range was found to be 2.3 × 10?20 cm2. The measured absorption cross section of 1.46 × 10?19 cm2 implies a quantum yield of 16% over this range. 相似文献
13.
The kinetic energy dependence of the charge reactions 3He+ + 4He ? 3He + 4He+ was investigated using a modified ion cyclotron double resonance technique. The rate constant increases monotonically from (5.0 ± 0.5) × 10?10 cm3 molecule?1 sec?1 at 0.1 eV to 55 × 10?10 cm3 molecule?1 sec?1 at a relative kinetic energy of 25 eV. The results compare favorably with theoretical predications for symmetric resonance charge transfer. 相似文献
14.
The proton formation by dissociative electroionization of methane has been investigated in the energy range of 25–40 eV. The kinetic energy-versus-appearance energy shows five different H+ producing processes respectively at 26.3 ± 0.2 eV, 26.9 ± 0.2 eV, 29.4 ± 0.3 eV, 32.7 ± 0.2 eV and 35.7 ± 0.5 eV. These critical energies are discussed in terms of different dissociation channels probably opened through predissociation of doubly excited states of CH+4. On the high energy side of the electron energy range investigated in the present work, the proton would appear through the dissociation of the CH+ ion as an intermediate. 相似文献
15.
In this paper we report the results of an experimental study of collision-free molecular multiphoton dissociation (MPD) and molecular multiphoton ionization (MPI) of nickelocene (NiC10H10), induced by the light of a tunable dye laser in the wavelength region 3750–5200 A. The spectral dependence of the ion signal reveals a multitude of narrow (fwhm from <0.5 cm?1 to 1.5 cm?1) intense peaks superimposed on a very weak background (relative amplitude ratio for peaks/background ≈ 103). The sharp resonances in the ion signal are attributed, on the basis of spectroscopic analysis, to two-photon resonant three-photon ionization of Ni(I) and to one-photon resonant three-photon ionization of Ni(I), the Ni(I) being produced by MPD of nickelocene. The ion signal in the spectral range 3750–3950 A reveals enhanced continuous background due to MPI of nickelocene. This ion signal spectra, together with studies of the intensity dependence of the overall (nickelocene MPD) - (Ni(I) MPI) processes, as well as the (nickelocene molecular MPI) reaction, reveal four reactive processes. (a) Two-photon molecular MPI for hω ? 3.10 eV photons. (b) Three-photon molecular MPI for hω = 3.10-2.10 eV. (c) Two-photon MPD at hω ? 2.86 eV. (d) Three-photon MPD for hω = 2.8-1.9 eV. The overall dissociation energy of nickelocene (Nicp2) to give Ni + 2cp was determined to be 5.76 ± 0.60 eV and the two-photon ionization potential of this molecule is 6.29 ± 0.015 eV. Our results provide dynamic evidence concerning a simultaneous “explosive” photodissociation mechanism of Nicp2 by process (c) and for the dominating role of the dissociative channel, characterized by a branching ratio of ?50 in favor of predissociation over autoionization, for process (c) at 6.3–6.6 eV. The MPD processes (c) and (d) are expected to exhibit intramolecular erosion of phase coherence effects. Processes (c) and (d) are of high efficiency ≈0.01 ions/molecule at saturation exhibited at laser power of ≈ 108 W cm?2. 相似文献
16.
Cross sections for the photodissociation of ground state CH+ ions through absorption into the A1Π state are calculated for the lowest three vibrational levels. At threshold the cross sections for υ″ = 0, 1 and 2 are respectively 5.0 × 10?20 cm2, 8.1 × 10?19 cm2 and 2.6 × 10?18 cm2. 相似文献
17.
The rate coefficients for the reaction OH + CH3CH2CH2OH → products (k1) and OH + CH3CH(OH)CH3 → products (k2) were measured by the pulsed‐laser photolysis–laser‐induced fluorescence technique between 237 and 376 K. Arrhenius expressions for k1 and k2 are as follows: k1 = (6.2 ± 0.8) × 10?12 exp[?(10 ± 30)/T] cm3 molecule?1 s?1, with k1(298 K) = (5.90 ± 0.56) × 10?12 cm3 molecule?1 s?1, and k2 = (3.2 ± 0.3) × 10?12 exp[(150 ± 20)/T] cm3 molecule?1 s?1, with k2(298) = (5.22 ± 0.46) × 10?12 cm3 molecule?1 s?1. The quoted uncertainties are at the 95% confidence level and include estimated systematic errors. The results are compared with those from previous measurements and rate coefficient expressions for atmospheric modeling are recommended. The absorption cross sections for n‐propanol and iso‐propanol at 184.9 nm were measured to be (8.89 ± 0.44) × 10?19 and (1.90 ± 0.10) × 10?18 cm2 molecule?1, respectively. The atmospheric implications of the degradation of n‐propanol and iso‐propanol are discussed. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 42: 10–24, 2010 相似文献
18.
The kinetics of the gas‐phase reactions of O3 with a series of selected terpenes has been investigated under flow‐tube conditions at a pressure of 100 mbar synthetic air at 295 ± 0.5 K. In the presence of a large excess of m‐xylene as an OH radical scavenger, rate coefficients k(O3+terpene) were obtained with a relative rate technique, (unit: cm3 molecule?1 s?1, errors represent 2σ): α‐pinene: (1.1 ± 0.2) × 10?16, 3Δ‐carene: (5.9 ± 1.0) × 10?17, limonene: (2.5 ± 0.3) × 10?16, myrcene: (4.8 ± 0.6) × 10?16, trans‐ocimene: (5.5 ± 0.8) × 10?16, terpinolene: (1.6 ± 0.4) × 10?15 and α‐terpinene: (1.5 ± 0.4) × 10?14. Absolute rate coefficients for the reaction of O3 with the used reference substances (2‐methyl‐2‐butene and 2,3‐dimethyl‐2‐butene) were measured in a stopped‐flow system at a pressure of 500 mbar synthetic air at 295 ± 2 K using FT‐IR spectroscopy, (unit: cm3 molecule?1 s?1, errors represent 2σ ): 2‐methyl‐2‐butene: (4.1 ± 0.5) × 10?16 and 2,3‐dimethyl‐2‐butene: (1.0 ± 0.2) × 10?15. In addition, OH radical yields were found to be 0.47 ± 0.04 for 2‐methyl‐2‐butene and 0.77 ± 0.04 for 2,3‐dimethyl‐2‐butene. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 394–403, 2002 相似文献
19.
《Chemical physics》1987,116(1):151-157
Relative photoexcitation spectra of ionic fragments SiH+3, SiH+2, SiH+ and Si+ originating from photofragmentation of molecular silane (SiH4) have been measured in the 12–19 eV region using a time-of-flight mass-analytic method combined with synchrotron radiation as a light source. No SiH+4 could be detected in a measurement time of a few microseconds. The excitation spectra show a maximum photoionization efficiency around 13.3 eV for SiH+2 and around 14.8 eV for SiH+3. Correlations between photoionization and dissociation are discussed. The assignment of the autoionization structure between 15 and 18 eV by Börlin et al. has been positively examined and extended to include two vibrational progressions composed of the ν1 mode with a frequency of 1690 ± 60 cm−1 and the ν2 mode with 730 ± 80 cm−1. 相似文献
20.
Timothy J. Wallington Loretta M. Skewes Walter O. Siegl Steven M. Japar 《国际化学动力学杂志》1989,21(11):1069-1076
The relative rate technique has been used to determine rate constants for the reaction of bromine atoms with a variety of organic compounds. Decay rates of the organic species were measured relative to i-butane or acetaldehyde or both. Using rate constants of 1.74 × 10?15 and 3.5 × 10?12 cm3 molecule?1 s?1 for the reaction of Br with i?butane and acetaldehyde respectively, the following rate constants were derived, in units of cm3 molecule?1 s?1: 2, 3?dimethylbutane, (6.40 ± 0.77) × 10?15; cyclopentane, (1.16 ± 0.18) × 10?15, ethene, (≤2.3 × 10?13); propene, (3.85 ± 0.41) × 10?12; trans-2-butene, (9.50 ± 0.76) × 10?12, acetylene, (5.15 ± 0.19) × 10?15; and propionaldehyde, (9.73 ± 0.91) × 10?12. Quoted errors represent 2σ and do not include possible systematic errors due to errors in the reference rate constants. Experiments were performed at 295 ± 2 K and atmospheric pressure of synthetic air or nitrogen. The results are discussed with respect to the mechanisms of these reactions and their utility in serving as a laboratory source of alkyl and alkyl peroxy radicals. 相似文献