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1.
This survey begins with the photochemistry at 254 nm and 298 K in the system H 2O 2COO 2RH, the primary objective of which is to determine the rate constants for the reaction OH + RH → H 2O + R relative to the well-known rate constant for the reaction OH + CO → CO 2 + H. Inherent in the scheme is that the reaction HO 2+CO→OH+CO 2 is negligible compared with the OH reaction, and a literature consensus gives kHO2 < 10 −19 cm 3 molecule −1 s −1, or some 10 6 less than kOH at 298 K. Theoretical calculations establish that the first stage in the HO 2 reaction is the formation of a free radical intermediate HO 2 + CO → HOOCO (perhydroxooxomethyl) which decomposes to yield the products, and that the rate of formation of the intermediate is equal to the rate of formation of the products. The structure of the intermediate and a reaction profile are shown. High temperature rate data reported subsequent to the data in the consensus and theoretical calculations lead here to a recommendation that, in the range 250–800 K, kHO2 = 3.45 × 10−12T1/2 exp(1.15 × 104/T) cm3 molecule−1 s−1, the hard-sphere-collision Arrhenius modification. This yields kHO2(298) = 1.0 × 10−27 cm3 molecule−1 s−1 or some 1014 slower than kOH(298). 相似文献
2.
A high-resolution emission spectrum of a low-pressure Ar-diluted CO + N 2O → CO 2 + N 2 flame catalyzed by Na metal vapor has been obtained and examined for vibrational disequilibrium. Emission in the 1900-2400 cm −1 spectral region, which includes the fundamental and “hot” bands of CO, CO 2(ν 3), and N 2O(ν 3), was recorded with high resolution and the CO emission was analyzed in detail to determine vibrational and rotational temperatures which were found to be unequal, Tv = 2050°K and TR = 1100°K. An examination of vib-vib and vib-trans energy transfer mechanisms results in the conclusion that an excess of 14% of the chemical energy is preferentially deposited in the resonantly-coupled N 2, CO, CO 2 (ν 3), and N 2O(ν 3) vibrational modes. It is further observed that CO vibrational levels for ν > 4 are excessively populated, presumably due to quenching of Na*(3p) by CO; the flame is accompanied by intense Na D-line chemiluminescence. 相似文献
3.
The Ca( 1D 2, 3P J) + CH 3 → CaI(A,B) + CH 3 reactions system has been studied by measuring its chemiluminescence under beam-gas conditions. Absolute values of the state-to-state reaction cross-sections were determined at low collision energy
. In addition, the electronic branching ratio and product energy disposal have been determined for each metastable reaction. The major changed observed in the chemiluminescence when comparing the Ca( 1D 2) reaction versus that of Ca( 3P J) is the total yield associated with the former reaction. To the best of our spectral resolution neither the electronic branching ratio e.g. CaI(A)/CaI(B) nor the internal CaI energy disposal change significantly as the metastable Ca( 1D 2)/Ca( 3P J) ratio is varied. In spite of the fact that the Ca( 3P J) reaction is less exoergic, the CaI product appears with a higher fraction of internal energy than that of Ca( 1D 2) reaction. Thus, the fraction of the total energy appearing in CaI internal energy amounts to 57.5% in the Ca( 3P J) reaction while it is 19.3% only for the Ca( 1D 2) reaction. This difference is discussed in the light of a distinct mechanism associated with the attack of the excited Ca atom into the C---I bond. No significant chemiluminescence yield was found for the energetically open CaCH *3 channels. The product chemiluminescence polarization was also measured as a function of the metastable concentration. A significant degree of polarization was found depending upon the specific electronic excitation. The analysis of the polarization emission associated to the parallel CaI(X 2Σ+ ← B 2Σ+) emission led into a strong polarization of the product rotational angular momentum. The comparison of the product rotational alignment for the kinematically identical Ca(1D2, 3PJ, 1P1) + CH3 → CaI* (B2Σ+) + CH3 reaction system showed that the CaI rotational polarization diminishes in the 3PJ → 1D2 → 1P1 sequence, e.g. as the reaction exothermicity increases. In addition the degree of polarization associated with other emission bands as for example CaI(X 2Σ+ ← A 2Π1/2) indicates the presence of a parallel transition which was been interpreted as mixing of Hund's case (a) and (c) appropriate for this heavy CaI diatom produced with a high rotational excitation. 相似文献
4.
Saddle point geometries and barrier heights have been calculated for the H abstraction reaction HO 2( 2A″)+H( 2S) → H 2( 1Σ +g)+O 2( 3Σ −g) and the concerted H approach-O removing reaction HO 2 ( 2A″)+H( 2S) → H 2O( 1A 1)+O( 3P) by using SDCI wavefunctions with a valence double-zeta plus polarization basis set. The saddle points are found to be of C s symmetry and the barrier heights are respectively 5.3 and 19.8 kcal by including size consistent correction. Moreoever kinetic parameters have been evaluated within the framework of the TST theory. So activation energies and the rate constants are estimated to be respectively 2.3 kcal and 0.4×10 9 ℓ mol −1 s −1 for the first reaction, 20.0 kcal and 5.4.10 −5 ℓ mol −1 s −1 for the second. Comparison of these results with experimental determinations shows that hydrogen abstraction on HO 2 is an efficient mechanism for the formation of H 2 + O 2, while the concerted mechanism envisaged for the formation of H 2O + O is highly unlikely. 相似文献
5.
The stoichiometry of the oxidation of IDA or NTA with lead dioxide suspension was studied by polarographic measurement and by derivative polarographic titration. One mole and two moles of Pb(IV) are reduced per mole of IDA and NTA respectively, with moderate speed at room temperature in nitric acid solutions. One mole each of carbon dioxide, formaldehyde and glycine are produced from the oxidation of 1 mole of IDA, and two moles of carbon dioxide, two moles of formaldehyde and one mole of glycine from 1 mole of NTA. The overall reaction in each case may be written as follows: Pb(IV) + IDA + H 2O → Pb(II) + CO 2 + HCHO + H 2NCH 2COOH + 2H + 2Pb(IV) + NTA + 2H 2O → 2Pb(II) + 2CO 2 + 2HCHO + H 2NCH 2COOH + 4H + 相似文献
6.
A mixture of NF 3 and Ar is passed through an rf discharge in a flow-system to produce, among other species, F and NF 2. When H 2, D 2, or CH 4 are added downstream, reactions with F atoms produce vibrationally excited HF or DF together with H, D, or CH 3. The latter free radicals can react with NF 2, probably by an elimination reaction to produce electronically excited NF: NF 2( 2B 1) + H(D, CH 3) → HF *(DF * + NF(a 1Δ). A vibrational-to-electronic energy transfer process between the products of this reaction then produces the next higher state of NF: HF(ν 2) + NF(a 1Δ) → HF(ν−2) + NF(b 1Σ +). A similar transfer process has also been found between the electronically excited a 1Δ states of O 2 and NF: O 2(a 1Δ) + NF(a 1Δ) → O 2(X 3Σ −) + NF(b 1Σ +). The H or D atoms but not the CH 3 radicals are then found to react with either NF(a 1Δ) or NF(X 3Σ −) to produce electronically excited N( 2D) atoms, which in turn react with the NF(a 1Δ) molecules to produce N 2(B 3Π g). The observed nitrogen first positive radiation has been demonstrated to be produced entirely by this reaction mechanism rather than by the N( 4S) recombination that accounts for the Rayleigh afterglow. In addition, the occurrence of the reaction N( 2D) + N 2O → NO(B 2Π r) + N 2 (X 1Σ +g) has been verified. Finally we have observed emission at 3344 Å, which we attribute to the NF(A 3Π), which has not been previously reported. 相似文献
7.
The thermal decomposition of CaOsO 3 by differential thermal analyses, thermogravimetry and X-ray powder diffraction has been studied. In nitrogen CaOsO 3 decomposes at 880 ± 10°C into CaO, osmium metal and oxygen due to the reaction CaOsO 3 → CaO + Os + O 2. In static air the decomposition occurs in three stages: 2CaOsO 3 + 1/2O 2 → Ca 2Os 2O 7 (in region 775–808°C), Ca 2Os 2O 7 → Ca 2Os 2O 6,5 + 1/4O 2 (at a temperature interval of 850–1000°C) and in the third stage Ca 2Os 2O 6,5 → 2CaO + OsO 4 ÷ 1/4 O 2 (at 1005 ± 5°C). The first intermediate Ca 2Os 2O 7 is isostructural with orthorhombic Ca 2Nb 2O 7 and its cell parameters are: a0 = 3.745 Å, b0 = 25.1 Å, c0 = 5.492 Å, Z = 4, space group Cmcm or Cmc2. Ca 2Os 2O 7 exhibits metallic conductivity and its electrical resistivity is 4.6 × 10 −2 ohm-cm at 296K. 相似文献
8.
The
and
-benzyl derivatives (1 and 2, respectively) of (+)-camphor have been synthesized and are found to exert a strong influence on the circular dichroism n→π * Cotton effects: 1: Δε 301max -0.36 (n- heptane) and 2: Δε 302max +3.22, relative to camphor: Δε 304max +1.8 (n-heptane). Evidence for electric dipole transition moment coupling in these γ, δ -unsaturated systems is found in the n→π * UV: 1: ε 291max 84 (n-heptane) and 2: ε 285max 303, relative to camphor: ε 290max 25. 相似文献
9.
S 0 → S 1 and S 0 → S 2 electronic transitions have been observed in UV–Visible absorption spectroscopy of 3-pyrazolyl-2-pyrazoline (PZ) in different homogeneous solvents. Radiative emissions and relaxation processes from S 1 and S 2 states of PZ have been resolved in water, ethylene glycol and glycerol whereas in polar aprotic and protic solvents the radiative transitions have been observed from S 1 state. The S 2–S 1 electronic energy spacing has been calculated from the absorption maxima of the S 0 → S 2 transitions and fluorescence maxima of the S 1 → S 0 transitions. Solute–solvent interactions have been established to rationalize the photophysical modification of PZ in H-bonding solvents. 相似文献
10.
The enthalpy change for anabolism is needed to model the growth/respiration relation in plants. If all CO 2 production is assigned to catabolism, the anabolic reaction becomes C substrate→C products+ xO 2 with an enthalpy change, Δ Hb. Four methods are proposed for determining Δ Hb: (a) From the difference in the heats of combustion of substrate and anabolic products (i.e. newly grown tissue). (b) From the composition of newly grown tissue and application of Thornton’s rule. (c) From independently measured values of the specific growth rate, RSG, and of the product ( RSG Δ Hb). The product ( RSG Δ Hb) equals (−Δ HCO2RCO2− Rq) where RCO2 is the specific rate of CO 2 production by respiration, Δ HCO2 is the heat of combustion of respiratory substrate per mole of CO 2 and Rq is the specific metabolic heat rate. Δ Hb is then calculated as the ratio ( RSG Δ Hb)/ RSG. (d) From (Δ Hb=−( Rq/ RCO2+Δ HCO2) [(1−)/] where is the substrate carbon conversion efficiency obtained from a total carbon balance. The first three methods have been tested and compared on oat seedlings and the last on corn seedlings. Δ Hb values from all four methods are in reasonable agreement despite the different assumptions involved. 相似文献
11.
The equilibrium geometries, excitation energies, force constants and vibrational frequencies for seven low-lying electronic states X 1A 1, 1B 1, 3B 1, 1A 2, 3A 2, 1B 2 and 3B 2 of dichlorocarbene CCl 2 have been calculated at the MRSDCI level with a double-zeta plus polarization basis set. Our calculated equilibrium geometry for the X 1A 1 state, excitation energy for X 1A 1 → 1B 1 and vibrational frequencies for the X 1A 1 and 1B 1 states are in good agreement with experimental data. The electronic transition dipole moments, oscillator strengths for the 1B 1 → X 1A 1 and 1B 2 → X 1A 1 transitions, radiative lifetimes for the 1B 1 and 1B 1 states are calculated using MRSDCI wavefunctions, predicting results in reasonable agreement with experiment. 相似文献
12.
Potential curves were calculated for eighteen low-lying doublet and quartet states of PN +, using configuration-interaction methods and double-zeta plus polarization and diffuse basis sets. Spectroscopic constants were evaluated for fourteen stable states. The X 2Σ + ground state lies very close to A 2Π (0.34 eV calculated). The 2 2Σ + state has two shallow minima of similar energy, being due to σ* → σ at smaller R, and π → π* at larger R. For N 2+, σ* → σ is much lower in energy than π → π*, whereas the opposite situation applies to P 2+. 相似文献
13.
A tandem quadrupole mass spectrometer is used to study the charge transfer reactions NH 3+ + NO and NO + + NH 3 over a collision energy range 1.5–13 eV. The vibrational state of the reagent ions is selected by resonance-enhanced multiphoton ionization. For the 0.9 eV exothermic process NH 3+ + NO → NH 3 + NO + excitation of the v2 umbrella bending mode ( v2 = 0–12) causes no marked change in the charge transfer cross section, while in the reverse process NO + + NH 3 → NO + NH 3+ excitation of the NO + vibration ( v = 0–6) strongly enhanced the charge transfer cross section. 相似文献
14.
Infrared photoisomerization of allylamine trapped in solid argon is studied by irradiation either at specific wavelengths emitted by a CO 2 laser in coincidence with bands of the three conformers (S + G +, ST and CT) or in several mid- or near-IR domains using broad band filters. Upon irradiation with broad band filters the CT → ST process is mainly observed whatever the frequency domain, with only a slight intensity increase of the S + G + bands. Upon irradiation with CO 2 lines in coincidence with CT bands the conversion CT → ST is observed; the reverse process is evidenced by irradiation at ST frequencies. Irradiation at S + G + frequency shows no effect on the conformational equilibrium. Kinetic rate constants are measured and normalized to constant light power absorbed by the sample. They are compared with those calculated by the RRKM theory of first-order processes, assuming the same torsional barrier around the C---C bond as in the gas phase. The good agreement between experimental and calculated values suggests the absence of vibrational selectivity in this photoisomerization process. 相似文献
15.
Rate constants for the tunneling reaction (HD + D → h + D 2) in solid HD increase steeply with increasing temperature above 5 K, while they are almost constant below 4.2 K. The apparent activation energy for the tunneling reaction above 5 K is 95 K, which is consistent with the energy (91–112 K) for vacancy formation in solid hydrogen. The results above 5 K were explained by the model that the tunneling reaction was accelerated by a local motion of hydrogen molecules and hydrogen atoms. The model of the tunneling reaction assisted by the local motion of the reactans and products was applied to the temperature dependence of the proton-transfer tunneling reaction (C 6H 6− + C 2H 5OH → C 6H 7 + C 2H 5O −) in solid ethanol, the tunneling elimination of H 2 molecule of H 2 molecule ((CH 3) 2 CHCH(CH 3) 2+ → (CH 3) 2 C = C(CH 3) 2+ + H 2) in solid 2,3-dimethylbutane, and the selective tunneling reaction of H atoms in solid neo-C 5H 12-alkane mixtures. 相似文献
16.
The 60-electron tetrahedral clusters W 2Ir 2(μ-L)(CO) 8(η 5-C 5H 4Me) 2 [L=dppe (2), dppf (3)] have been prepared from reaction between W 2Ir 2(CO) 10(η 5-C 5H 4Me) 2 (1) and the corresponding diphosphine in 52 and 66% yields, respectively. A structural study of 2 reveals that three edges of a WIr 2 face are spanned by bridging carbonyls, that the iridium-ligated diphosphine coordinates diaxially and that the tungsten-bound methylcyclopentadienyls coordinate axially and apically with respect to the plane of bridging carbonyls. A structural study of 3 reveals that the dppf ligand bridges an Ir---Ir bond which is also spanned by a bridging carbonyl; tungsten-ligated methylcyclopentadienyl ligands and terminal carbonyls result in electronic asymmetry (17e and 19e iridium atoms) in the electron-precise cluster. Both clusters show two reversible one-electron oxidation processes and an irreversible two-electron reduction; the dppf-containing cluster 3 has a further, irreversible, one-electron oxidation process. UV–vis-NIR spectroelectrochemical studies of the 2→2 +→2 2+ progression reveal the appearance of a low-energy transition on oxidation to 2 + which persists on further oxidation to 2 2+. 相似文献
17.
The stability criteria of liquid foams, stabilized by solid particles have been derived, based on the interfacial separating pressure, acting between two neighboring bubbles (foam cells). Different structures of solid particles in the cell walls have been considered, all being able to stabilize liquid foams with an increasing probability, according to the following row: structure LP1 (loosely packed single layer of particles) → structure CP1 (closely packed single layer of particles) → structure LP2C (loosely packed double layer of clustered particles) → structure LP2+C (loosely packed ‘double+’ layer of clustered particles) → structure CP2 (closely packed double layer of particles) → structure CP2+ (closely packed ‘double+’ layer of particles). It has been shown that the contact angle should be higher than a certain value Θo, in order to ensure stability of bubble–particles agglomerates. On the other hand, different structures of particles can stabilize the foam, if the contact angle is below the certain value (90° for the CP1 and LP1 structures, 129° for the CP2, LP2C and LP2+C structures and 180° for the CP2+ structure). The optimum value of the contact angle, being able to stabilize the foam is a difficult function of different parameters, but has been found in the interval between 50 and 90°. It has been shown that the possibility to stabilize liquid foams is connected with the value of the dimensionless quantity PRs/ σ ( P: the pressure, destabilizing the foam; Rs: the radius of the stabilizing particles; σ: the surface tension of the liquid). When PRs/σ>40, foam stabilization is absolutely impossible. When PRs/σ<40, foam stabilization becomes possible, but it has high probability only at PRs/σ<4. From this condition the maximum size of the particles, being able to stabilize liquid foams can be found. Trial calculations showed that particles smaller than 3 and 30 μm in diameter are requested for stabilizing water based, and liquid aluminum based foams, respectively. 相似文献
18.
The quantum yield ratio r = φ 2 → 0/φ 2 → 1 of the S 2 → S 0 and S 2 → S 1 fluorescences from azulene has been redetermined. With azulene in isopentane at 190 K, r = 455 ± 100. This value agrees with the lower limit, given by Huppert, Jortner and Rentzepis, but is an order of magnitude lower than that given by Gillispie and Lim. 相似文献
19.
CAS SCF and CCI calculations have been performed in order to establish the existence or non-existence of the HO 3 radical. The potential surface for the dissociation reaction, HO 3 → O 2( 3Σ) + OH, along one chosen coordinate has been calculated. The calculations show that although the wavefunctions describing the short-distance and long-distance states are of different character, the energies are the same and the curve connecting the states is very flat. There is probably no barrier towards dissociation of the radical. However, the existence of HO 3 can still not be excluded. 相似文献
20.
The absolute thermal rate coefficient for the reaction NH 3+ + NH 3 → NH 4+ + NH 2 has been determined experimentally for the first time for NH 3+ (ν = 0) reactant ions. An increase in Evib results in a decrease in the rate coefficient for proton transfer. 相似文献
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