The theory presented in part I of this series is applied to the non-adiabatic spin-forbidden thermal dissociation N2O(1Σ+)→N2(1Σ+g)+O(3P) as a test case. The molecular model is multidimensional and includes all vibrational modes of the molecule. Specifically considered is the fact that the initial singlet state of N2O is linear and the final triplet state is bent. The best available data are used for describing the intersection of singlet and triplet potential energy surfaces. Calculated microcanonical rate constants are averaged over Boltzmann distribution of energies and compared with kco, the high-pressure rate constant deduced from experiment. The agreement between theory and experiment is satisfactory. Analysis of the calculations shows that the driving force for the N2O dissociation is the flow of energy into the bending vibrations. This is because the bendings have very different equilibrium angles in the initial and final states. 相似文献
The competition between ion dissociation and ion ejection during resonant excitation in a quadrupole ion trap is investigated. Ions of similar mass but with a range of critical energies for the onset of dissociation have been examined. The effects of the amplitude and duration of the resonant excitation, the well depth in which the ions are trapped, and the pressure and nature of the collision gas are explored. Once the onset of ion ejection is reached, the rate of ion ejection increases with increased amplitude of the resonant excitation signal. The rate of ejection decreases or stays constant as a function of the duration of the resonant excitation, depending upon the ion species being excited. Increasing the trapping well depth increases the relative amount of dissociation versus ejection as does increasing the pressure of the bath gas. Adding heavier bath gases lowers the onset of ion dissociation and raises the onset of ion ejection. 相似文献
The solubility of N2, N2O, and NН3 is studied in different organic solvents. The best dissolution (0.27 ppm) is found to be for N2O in perfluorodecalin at 291 K and a pressure of 99 kPa. The dependence of N2O solubility in perfluorodecalin on pressure is studied at 291 K. The Gibbs energy of the solubility of nitrogen, nitrous oxide, and ammonia in perfluorodecalin is calculated. 相似文献
The reaction of C2H6with lattice oxygen, O2- (in the absence of gaseous oxygen), or “adsorbedℍ oxygen (in the presence of gaseous oxygen) over NiMoO4 catalysts has been performed and compared to C3H8 activation. The results obtained indicate that adsorbed oxygen exhibits a higher reactivity to C2H6, while lattice oxygen is more reactive relative to C3H8. Kinetic studies of these two reactions in presence of molecular oxygen have indeed shown that the ethane oxidative dehydrogenation
(ODH) is dependent on the oxygen partial pressure, whilst on the contrary propane ODH is not. In order to confirm the presence
of “adsorbed” oxygen for ethane activation, ODH tests have been performed with N2O. On increasing temperature, the O- adsorbed species enhances the mild oxidation of ethane. The activation energy of ethane consumption EC2H6, relative to propane (EC3H8 = 133 kJ/mol) is 145 kJ/mol. A possible mechanism is proposed for the oxidative dehydrogenation of ethane.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
We demonstrate a high-precision measurement of the isotopomer abundance ratio 14N(15)N(16)O/15N(14)N(16)O/14N(14)N(16)O (approximately 0.37/0.37/100) using three wavelength-modulated 2 microm diode lasers combined with a multipass cell which provides different optical pathlengths of 100 and 1 m to compensate the large abundance difference. A set of absorption lines for which the absorbances have almost the same temperature dependence are selected so that the effect of a change in gas temperature is minimized. The test experiment using pure nearly natural-abundance N(2)O samples showed that the site-selective 15N/14N ratios can be measured relative to a reference material with a precision of +/-3 x 10(-4) (+/-0.3 per thousand) in approximately 2 h. 相似文献
The authors use transient absorption spectroscopy to monitor the ionization and dissociation products following two-photon excitation of pure liquid water. The primary decay mechanism changes from dissociation at an excitation energy of 8.3 eV to ionization at 12.4 eV. The two channels occur with similar yield for an excitation energy of 9.3 eV. For the lowest excitation energy, the transient absorption at 267 nm probes the geminate recombination kinetics of the H and OH fragments, providing a window on the dissociation dynamics. Modeling the OH geminate recombination indicates that the dissociating H atoms have enough kinetic energy to escape the solvent cage and one or two additional solvent shells. The average initial separation of H and OH fragments is 0.7+/-0.2 nm. Our observation suggests that the hydrogen bonding environment does not prevent direct dissociation of an O-H bond in the excited state. We discuss the implications of our measurement for the excited state dynamics of liquid water and explore the role of those dynamics in the ionization mechanism at low excitation energies. 相似文献
A mass spectrometric method to determine the absolute intramolecular (position-dependent) nitrogen isotope ratios of nitrous oxide (N2O) has been developed. It is based on the addition of different amounts of doubly labeled 15N2O to an N2O sample of the isotope ratio mass spectrometer reference gas, and subsequent measurement of the relative ion current ratios of species with mass 30, 31, 44, 45, and 46. All relevant quantities are measured by isotope ratio mass spectrometers, which means that the machines inherent high precision of the order of 10–5 can be fully exploited. External determination of dilution factors with generally lower precision is avoided. The method itself can be implemented within a day, but a calibration of the oxygen and average nitrogen isotope ratios relative to a primary isotopic reference material of known absolute isotopic composition has to be performed separately. The underlying theoretical framework is explored in depth. The effect of interferences due to 14N15N16O and 15N14N16O in the 15N2O sample and due to 15N
2+
formation are fully accounted for in the calculation of the final position-dependent nitrogen isotope ratios. Considering all known statistical uncertainties of measured quantities and absolute isotope ratios of primary isotopic reference materials, we achieve an overall uncertainty of 0.9 (1). Using tropospheric N2O as common reference point for intercomparison purposes, we find a substantially higher relative enrichment of 15N at the central nitrogen atom over 15N at the terminal nitrogen atom than measured previously for tropospheric N2O based on a chemical conversion method: 46.3±1.4 as opposed to 18.7±2.2. However, our method depends critically on the absolute isotope ratios of the primary isotopic reference materials air–N2 and VSMOW. If they are systematically wrong, our estimates will also necessarily be incorrect. 相似文献
Summary A simple dual-column system with a thermal conductivity detector is described, that can be used for the quantitative analysis of anesthetic gas mixtures of halothane (2-bromo-2-chloro-1,1,1-trifluoroethane), nitrous oxide and oxygen. The separation was performed on a Carbopack (SP 1000) column and a Porapak Q column arranged in series across the detector. 相似文献
Resolution improvements in dipolar resonant excitation have been examined in a round-rod quadrupolar collision cell for values of the Mathieu characteristic exponent beta equal to n/p, where n and m are small integers (prime beta values) versus other beta values where n and p are not small (ordinary beta values). The trajectories of ions moving in the time-varying electric fields of a quadrupole with and without buffer-gas molecules were calculated to determine the relationship of prime and ordinary beta values to frequency resolution for resonant ion excitation and ejection. For prime beta values, the ion trajectory in the hyperbolic quadrupole field will be exactly periodic with a period of at most 4 pi p/Omega, where Omega is the angular frequency of the main drive radio-frequency (RF) potential. Ion trajectory simulations with prime beta versus ordinary beta values show that the motion of ions with prime beta values have simpler trajectories of shorter periods. Frequency response profiles (FRPs) for round-rod quadrupoles at zero pressure show that dipolar resonant excitations with prime beta values exhibit significantly narrower bandwidths than those with ordinary beta values. Simulations show that at 0.05 to 0.8 mTorr of nitrogen, it is possible to reduce the FRP bandwidth by 20% (measured at 50% depth). 相似文献
The oxidative dehydrogenation of propane has been studied with nitrous oxide (or mixture of nitrous oxide and oxygen) as oxidant.
Nitrous oxide is a more selective but less active oxidant as compared with molecular oxygen. Upon increasing the concentration
of N2O in the reaction mixture of propane and oxygen results in a substantial increase of propane conversion, while the selectivity
to propene remains constant. The synergistic effect of O2 and N2O leads to a threefold higher yield of propene relative to than that of oxygen or nitrous alone.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
The addition of molecular oxygen to the 147 nm photolysis of gaseous 1,2-butadiene leads to a large increase in the propene quantum yield. We have shown that this propene formation is linked to the production of oxygen atoms through the direct photolysis of molecular oxygen. Moreover, from the study of mixtures of nitrous oxide and 1,2-butadiene, it can be seen that O(3P), O(1D) and O(1S) atoms react with butadiene in similar reactions, and that O(1D) and O(1S) have reaction rates similar to their collision rate: 相似文献
The saturation concentrations of O2 and N2O in aqueous solution were measured for different amounts of NaCl by observing the decay of the absorption of hydrated electrons, which were generated during the radiolysis of water. The results are in good agreement with an empirical model based on numerous static measurements of the “salting-out” effect. 相似文献
A reference gas mixture of nitrous oxide (N2O) in nitrogen, filled in a 10-L high-pressure aluminum alloy gas cylinder, has been developed as a certified reference material for emission measurement of exhaust gases from automobiles. As an example of certified values, mole fraction of N2O is 302.36 μmol/mol. An electronic mass comparator with a home-made automatic cylinder exchanger, gas-filling equipment, and a gas chromatograph with a thermal conductivity detector have been used for the production of this CRM. The gas chromatographic analysis has of sufficient precision. The mole fraction of N2O has good long-term stability for 10 years and is independent of inner pressure in the gas cylinder. As these results, a relative expanded uncertainty (coverage factor is 2) of the certified value has become 0.28 %. This sufficiently small uncertainty of the N2O mole fraction will be advantageous in the calibration of analytical instruments for emission gas analysis. 相似文献
The mechanism of resonant multiphoton ionization dissociation (RMPID) of p-xylene is investigated theoretically based both on the quantum-mechanical MO calculation of the geometrical structures and dissociation energies of the fragments and on the computation of laser power-dependent mass spectra of the fragments produced by RMPID. The geometries and dissociation energies are calculated by using both the MNDO method and the ab initio method with the 6-31G basis set. The computation of the mass spectra is carried out in the absorption multiple fragmentation model. It is shown theoretically that the two-independent reaction sequence mechanism proposed by Takenoshita et al. upon measuring the laser power dependence can explain semi-quantitatively the mass spectra of the RMPID. From comparison of the measured mass spectra with the calculated ones it is suggested that the absorption multiple fragmentation model originally based on the product phase space theory can be applied to the RMPID involving transition states in the course of reactions such as the retro-Diels-Alder reaction C5H+5 → C3H+3 + C2H2 by taking into account the corresponding activation energy instead of the dissociation energy. 相似文献