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1.
Previous works have reported vibration—vibration and vibration—translation transfer rates in the methyl halides. Using the technique of laser induced infrared fluorescence we have studied energy transfer in the concluding member of this series, CH 3I. Following excitation by resonant lines of a Q-switch CO 2 laser, infrared fluorescence has been observed from the v2, v5 as well as the 2 v5, v1, v4 vibrational energy levels of CH 3I. All the observed states exhibit a single exponential decay rate of 23 ± 2 ms ?1 torr ?1. Measurements have also been made on deactivation of the various modes by rare gases. The risetime of the v2, v5 levels was found to be approximately 101 ± 20 ms ?1 torr ?1, while that of the 2 v5, v1, v4 levels was approximately 225 ± 45 ms ?1 torr ?1. Fluorescence was not detected from the v3 level. These results are discussed in terms of SSH type theoretical calculations, and comparison is made with the results obtained for other members of the methyl halide series, namely CH 3F, CH 3Cl and CH 3Br. 相似文献
3.
A study is made of the visible chemiluminescence resulting from the reaction of an atomic beam of barium with I Z under single-collision conditions (~ 10 ?4 torr). The resulting spectrum consists of the BaI C 2Π → X 2Σ emission on top of an underlying “continuum”. The variation of the BaI emission intensity with Ba and I 2 flux is investigated, and it is concluded that the reaction is bimolecular. The total phenomenological cross section for barium atom removal is determined to be 86 A 2, which agrees well with the total reactive cross section calculated assuming an electron jump mechanism. The short wavelength cutoff is identified as the transition from the υ′ = 41 level of the BaI C 2Π state to the υ′ = 41 level of the BaI X 2Σ state. A strict lower bound Do0(BaI) ? 102 ± 0.7 kcal/mole for the ground state dissociation energy of BaI is obtained from this short wavelength cutoff. The value Do0(BaI) = 102 ± 1 kcal/mole is recommended, where the error estimate includes the possible contribution from the final relative translational energy of the products. 相似文献
4.
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
6.
Infrared fluorescence has been observed from the ν 1, ν 6, 2ν 9, ν 8 and ν 4 levels of CH 2F 2 following excitation by a 9.6 μ Q-switch CO 2 laser. All the observed states exhibit a single exponential decay rate of approximately 44 msec ?1 torr ?1. The rare gas dependence of this rate has also been measured and found to be up to 20 times slower than the rate for the pure gas. Measurements of the risetimes of the observed fluorescence signals yielded an upper limit of 5 μsec at 1 torr for the ν 1, ν 6 and ν 8 levels. The 2ν 9 and ν 4 risetimes were effectively instantaneous under the experimental conditions that prevailed. The relative magnitudes of the measured rate are discussed in terms of existing V-T/R theories and collisional energy transfer processes. 相似文献
7.
Triplet methylene, CH 2( 3B 1), and methyl radicals were produced by flash photolysis of a mixture of ketene and azomethane. A computer fit of the product ratios, using the known rate constants for CH 2 + CH 2, and CH 3 + CH 3, requires a rate constant of 5.0 × 10 ?11 cm 3 molecule ?1s ?1 for the reaction CH 2 + CH 3 ? C 2H 4 + H. 相似文献
8.
In this paper we explore and develop the possibility of inverting kinetic data through effective optical potentials. Using arguments based on the so-called optical model of reaction dynamics, but without actually explicitly determining the effective potential, it is possible to carry out an inversion and correlation of molecular dynamics experiments. For example, by making a single reasonable assumption concerning the general features of the effective potential, one can invert the total reaction cross section as a function of collision energy to obtain reaction probabilities as a function of both impact parameter and energy for the reactions of K with CH 3I. Although the present technique represents only a lowest order approximation to the optical inversion of molecular kinetics experiments, there is good agreement with the trajectory calculations of LaBudde et al. Furthermore, it should be possible to improve upon the method, either by a more explicit determination of the properties of the optical potential or by using a more rigorously defined effective potential for the inversion process. 相似文献
9.
采用MP2(full)/6-311G(d, p)从头算方法,优化了硝基甲烷和甲基自由基吸氢反应的过渡态结构,经QCISD(T)方法进行能量校正,得出该反应的正逆向反应的活化位垒分别是58.21 kJ•mol-1和67.17 kJ•mol-1.沿IRC分析指出该反应是氢转移协同反应,而且在反应途径上存在一个引导反应进行的振动模式,这一反应模式引导反应进行的区间在反应坐标S的-0.9~1.0(amu)1/2bohr之间;在温度为800~2600 K范围内,运用改进的变分过渡态理论(ICVT),计算了该反应的速率常数,并与实验类比所得的速率常数随温度的变化趋势进行了比较. 相似文献
10.
We have compared the performance of CF 3I, CD 3I, and CH 3I in an atomic iodine photodissociation laser over the pressure range 1–200 torr. At pressures below 5 torr, CD 3I produces larger energy outputs, while above 5 torr CF 3I gives superior performance. The crossing of the laser energy output versus pressure curves is explained on the basis of collisional quenching of I( 2P )(≡I *) by undissociated alkyl iodide. 相似文献
11.
The mechanisms of the CH2+ O2→ H2O+ CO and CH2+ O2→ H2+ CO2 reactions have been studied by performing ab initio CAS(8,8)/6-31G(d,p) calculations, and five intermediates(IMn) and eight transitions(TSn) have been located along the reaction paths. The predicted path for the CH2+ O2→ H2O+ CO is: CH2+ O2→ TS1→ IM1→ TS2→ IM2→ TS3→ IM3→ TS4→ IM4a→ TS5→ H2O+ CO. For the CH2+ O2→ H2+ CO2 reaction, there are two paths: (i) CH2+ O2→ TS1→ IM1→ TS2→ IM2→ TS3→ IM3→ TS6→ H2+ CO2 and (ii) CH2+ O2→ TS1→ IM1→ TS2→ IM2→ TS3→ IM3→ TS4→ IM4a→ TS7→ IM4b→ TS8→ H2+ CO2, with the latter path more favorable energetically. 相似文献
12.
We have applied cavity ring-down spectroscopy to a kinetic study of the reaction of NO 3 with CH 2I 2 in 25–100 Torr of N 2 diluent at 298 K. The rate constant of reaction of NO 3 + CH 2I 2 is determined to be (4.0 ± 1.2) × 10 −13 cm 3 molecule −1 s −1 in 100 Torr of N 2 diluent at 298 K. The rate constant increases with increasing pressure of buffer gas below 100 Torr. The reaction of CH 2I 2 with NO 3 has the potential importance at nighttime in the atmosphere. 相似文献
13.
The abstraction reaction of methylene with hydrogen reinvestigated with a double zeta plus polarization basis at the configuration interaction level. The results are found to be very similar to those previously obtained without polarization functions, in line with previous findings at the SCF level. The barrier is computed to be 11.8 kcal/mole when an estimate of the effect of quadruple excitations is included. 相似文献
14.
1,2-Eliminations are a varied and extensive set of dissociations of ions in the gas phase. To understand better such dissociations,
elimination of CH 2=CH 2 and CH 3CH 3 from (CH 3) 2NH +CH 2CH 3 ( 1) and of CH 4 from (CH 3) 2NH 2+ are characterized by quantum chemical calculations. Stretching of the CN bond to ethyl is followed by shift of an H from
methyl to the bridging position in ethyl and then to N to reach (CH 3) 2NH 2+ + CH 2=CH 2 from 1. CH 3CH 3 elimination by H-transfer to C 2H 5+ to form CH 3NH +=CH 2 + CH 3CH 3 also takes place. (CH 3) 2NH 2+ eliminates methane by CN bond extension followed by β-H-transfer to give CH 2=NH + + CH 4. Low-energy reactions resembling complex-mediated 1,2-eliminations occur and constitute a hitherto largely unrecognized type
of reaction. As in many complex-mediated reactions, these reactions transfer H between incipient fragments. They are distinguished
from complex-mediated processes by the fragments not being able to rotate freely relative to each other near the transition
state for reaction, as they do in complexes. Most 1,2-eliminations are ion-neutral complex-mediated, occur by the just described
lower energy reactions, have 1,1-like transition states, or utilize highly asynchronous 1,2 transition states. All of these
avoid synchronized 1,2-transition states that would violate conservation of orbital symmetry. 相似文献
15.
The reactions of CH 3O 2 with SO 2 and NO have been studied by steady state photolysis of azomethane in the presence of O 2SO 2→NO mixtures at 296 K and 1 atm total pressure. The quantum yield of NO oxidation by CH 3O 2 radicals is increased substantially when SO 2 is added to the system indicating an SO 2 induced chain oxidation of NO. The rate law gives k1/ k2 = (2.5 ± 0.5) × 10 ?3 for CH 3O 2 + SO 2 → CH 3O 2SO 2 (1), CH 3O 2 + NO → CH 3O + NO 2 (2). Combining this ratio with the absolute value of k1 = 8.2 × 10 ?15 cm 3 s ?1 gives k2 = 10 ?11.5 ± 02 cm 3 s ?1. 相似文献
16.
Isochoric PVTx measurements have been performed for the binary system of nitrous oxide + CH 3F (R41), +CH 2F 2 (R32), and +CHF 3 (R23) using a new experimental set-up. The experiments covered both the two-phase region and the superheated vapor region and were performed within the temperature range 214–358 K and within a pressure range from 270 to 5600 kPa. Data have been collected for not less than four compositions for each system. The vapor–liquid equilibrium data were derived correlating the experimental data by means of the Carnahan–Starling–De Santis equation of state. The studied systems show a positive deviation from the Raoult's law. The results obtained were compared with the Burnett PVTx data. The two methods showed a mutual consistency within an acceptable margin of error. No other experimental PVTx data were found in the literature for these binary systems. 相似文献
17.
The effect on the thermal rate constant and the differential cross-sections of varying the dimensionality of quantum scattering calculations of a polyatomic reaction is investigated. The rotating bond approximation (RBA; 3D) and a rotating line approximation (RLA; 2D) are used for the CH 4 + OH → CH 3 + H 2O reaction. It is found that the RBA and RLA results are in close agreement when an adiabatic treatment is used for the degree of freedom which is treated explicitly in the RBA but not in the RLA. 相似文献
18.
Experimental evidence supporting the “direct” reaction model and the “intermediate complex” model for the reaction CH 3+(CH 4, H 2)C 2H 5+ are analysed. It is shown that the evidence for the former can equally well be interpreted in terms of a proposed model of persistent complex formation and decay. The plausibility of a “direct” mechanism is discussed and is found to be poor. 相似文献
19.
Photoacoustic measurements are described giving branching ratios for the I( 2P ) and I( 2P ) atom production following vapour-phase photolysis of CH 3I. A range of excitation wavelengths are used from the long wavelength tail up to 248 nm. The presence of three bands is shown within the σ * ← n continuum; in the strong-coupling model these are E ← A 1(⊥), A *1 ← A 1(||) and E ← A 1(⊥) with only the A *1 ← A 1 transition giving excited iodine atoms. 相似文献
20.
The kinetics of the reaction of the CH 3CHBr, CHBr 2 or CDBr 2 radicals, R, with HBr have been investigated in a temperature-controlled tubular reactor coupled to a photoionization mass spectrometer. The CH 3CHBr (or CHBr 2 or CDBr 2) radical was produced homogeneously in the reactor by a pulsed 248 nm exciplex laser photolysis of CH 3CHBr 2 (or CHBr 3 or CDBr 3). The decay of R was monitored as a function of HBr concentration under pseudo-first-order conditions to determine the rate constants as a function of temperature. The reactions were studied separately from 253 to 344 K (CH 3CHBr + HBr) and from 288 to 477 K (CHBr 2 + HBr) and in these temperature ranges the rate constants determined were fitted to an Arrhenius expression (error limits stated are 1σ + Student’s t values, units in cm 3 molecule −1 s −1, no error limits for the third reaction): k(CH 3CHBr + HBr) = (1.7 ± 1.2) × 10 −13 exp[+ (5.1 ± 1.9) kJ mol −1/ RT], k(CHBr 2 + HBr) = (2.5 ± 1.2) × 10 −13 exp[−(4.04 ± 1.14) kJ mol −1/ RT] and k(CDBr 2 + HBr) = 1.6 × 10 −13 exp(−2.1 kJ mol −1/ RT). The energy barriers of the reverse reactions were taken from the literature. The enthalpy of formation values of the CH 3CHBr and CHBr 2 radicals and an experimental entropy value at 298 K for the CH 3CHBr radical were obtained using a second-law method. The result for the entropy value for the CH 3CHBr radical is 305 ± 9 J K −1 mol −1. The results for the enthalpy of formation values at 298 K are (in kJ mol −1): 133.4 ± 3.4 (CH 3CHBr) and 199.1 ± 2.7 (CHBr 2), and for α-C–H bond dissociation energies of analogous compounds are (in kJ mol −1): 415.0 ± 2.7 (CH 3CH 2Br) and 412.6 ± 2.7 (CH 2Br 2), respectively. 相似文献
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