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1.
The study of intermolecular energy transfer in the 1,1-cyclopropane-d2 system has been repeated for the neat gas at 973 K and has been extended to krypton bath gas at 823 K and 973 K. The method of study is by the competitive collisional activation “spectroscopy” technique for this two-channel competitive isomerization system. Results at 823 K give the relative collisional efficiency of krypton as β ≈ 0.46, at k/k ≈ 0.02 and yield the average down-jump energy step as 〈ΔE〉 ≈ 1200 cm?1 on the basis of a stepladder model for the distribution of down-step sizes. At 973 K and k/k = 0.02, β ≈ 0.07 and 〈ΔE〉 ≈ 500 cm?8, for both an exponential and stepladder distribution of down-step sizes. Agreement with related earlier data for other bath gases and for neat cyclopropane is good and verifies again a decrease in energy transfer collisional efficiency, and a decrease in 〈ΔE〉, with rise of temperature, as previously reported for this system.  相似文献   

2.
The probability of reaction of cyclobutane molecules in a fixed time interval after experiencing a known variable number of collisions with a hot surface at temperatures between 749 K and 1126 K has been determined using the Variable Encounter Method. Calculations utilizing exponential or gaussian models for energy transfer enable the average amounts of energy transferred for deactivating collisions, <ΔE′?, to be estimated. The exponential model fits the experimental data the best and, using this model, <ΔE′? is 2430 cm?1 at 749 K and decreases to 1470 cm?1 at 1126 K. Incubation times are derived from the mean first passage times.  相似文献   

3.
The average downward energy transfer (〈Δ Edown〉) is obtained for highly vibrationally excited acetyl chloride with Ne and C2H4 bath gases at ca. 870 K. Data are obtained by the technique of very low-pressure pyrolysis (VLPP). Fitting these data by solution of the appropriate reaction-diffusion integrodifferential master equation yields the gas/gas collisional energy transfer parameters: 〈Δ Edown〉 values are 220 ± 10 cm?1 (Ne bath gas) and 330 ± 20 cm?1 (C2H4). These energy transfer quantities are much less than those predicted by statistical theories, or those observed for similar sized molecules such as CH3CH2Cl. These results are explained by the qualitative predictions of the biased random walk model wherein the fundamental mechanism of energy transfer is the multiple interactions between the bath gas and the individual atoms of the reactant molecule, during the course of the collision event. The charge distribution of acetyl chloride decreases the number of such interactions, thereby reducing the amount of energy transferred per collision.  相似文献   

4.
Intermolecular energy transfer has been studied in the two-channel competitive isomerization of 1,1-cyclopropane-d2, both in the neat system and in the presence of helium bath gas at values of k/k? centered around 0.02. The competing path ways differ in threshold energy by ≈ 0.6 kcal. The temperature range 773 K to 973 K was covered. Several methods of treating the data, whether by isotopic ratios of rate constants or by temperature dependence of fall off, are each independent of a knowledge of collision cross sections. Used in conjunction, they provide measurements of these quantities. Cyclopropane is an operationally strong collider (βω = 1) for itself at 773 K with an average down step size, <ΔE/s> >/ 10 kcal mole ?1 (>/ 3500 cm?1). At 973 K the substrate is no longer a strong collider; βω declines to ≈ 0.55 with <ΔE/s> ≈ 5.2 kcal mole?1. For helium the corresponding quantities are βω ≈ 0.078 <ΔE/s> ≈ 1.1 kcal mole ?1 declining to βω ≈ 0.010 and <ΔE/s> ≈ 0.53 kcal mole?1. The several methods of measuring these quantities give excellent independent agreement. Comparison with the earlier theoretical formulation of Tardy and Rabinovitch gives good agreement, the temperature dependence of βω for the weak collider, helium, follows the relation βωT?m, where m /s> 2.  相似文献   

5.
Changes in the magnitude of 〈ΔEdown〉, the average downward collisional energy transferred between a highly vibrationally excited reactant molecule and an inert bath gas, upon perdeuteration of the substrate are reported for tert-butyl bromide dilute in Ar, Kr, N2, and CO2. The technique of pressure-dependent very low-pressure pyrolysis (VLPP) was used to obtain the absolute values of 〈ΔEdown〉, which are for C4H9Br, 230 (Ar), 285 (Kr), 270 (N2), and 365 (CO2) while for C4D9Br, 200 (Ar), 250 (Kr), 220 (N2), and 335 (CO2), all in cm?1 at ca. 720 K. The estimated uncertainties in these values are ca. ± 10%. These observed 〈ΔEdown〉, values and trends found with results from this series of isotope studies, are compared with current theoretical models. Extrapolated high-pressure temperature-dependent rate coefficients (s?1) for the thermal decomposition of reactant are 1013.8±0.3 exp(?175 ± 8 kJ mol?1/RT) for C4H9Br and 1014.3±0.3 exp(?183 ± 8 kJ mol?1/RT) for C4D9Br. These results are in accord with other studies and the expected isotope effect.  相似文献   

6.
Values for 〈ΔEdown〉, the average downward energy transferred from the reactant to the bath gas upon collision, have been obtained for highly vibrationally excited undeuterated and per-deuterated isopropyl bromide with the bath gases Ne, Xe, C2H4, and C2D4, at ca. 870 K. The technique of pressure-dependent very low-pressure pyrolysis (VLPP) was used to obtain the data. For C3H7Br, the 〈ΔEdown〉 values (cm?1) are 490 (Ne), 540 (Xe), 820 (C2H4), and 740 (C2D4), and for C3D7Br, 440 (Ne), 570 (Xe), 730 (C2H4), and 810 (C2D4). The uncertainties in these values are ca. ±10%. The 〈ΔEdown〉 values for the inert bath gases Ne and Xe show excellent agreement with the theoretical predictions of the semi-empirical biased random walk model for monatomic/substrate collisional energy exchange [J. Chem. Phys., 80 , 5501 (1984)]. The relative effects of deuteration of the reactant molecule on 〈ΔEdown〉 also compare favorably with the predictions of this theoretical model. Extrapolated high-pressure rate coefficients (s?1) for the thermal decomposition of reactant are 1013.6±0.3 exp(?200 ± 8 kJ mol?1/RT) for C3H7Br and 1013.9±0.3 exp(?207 ± 8 kJ mol±1/RT) for C3D7Br, which are consistent with previous studies and the expected isotope effect.  相似文献   

7.
Rate coefficients for the collisional quenching of O2*(1Δg) by NO and CO2 at 2–8 torr and 300 K have been determined. kNO = (2.48 ± 0.23) × 10?17 cm3 molecule?1 s?1 and
= (2.56 ± 0.12) × 10?18 cm3 molecule?1 s?1.  相似文献   

8.
Spin—orbit relaxation of I(52P12)(ΔE = 0.94 eV) by benzene-d6, has been studied at 297 K, using time-resolved atomic resonance fluorescence. A large isotope effect is observed, kC6H6 = (4.6 ± 0.7) × 10?13 cm3 molecule?1 s?1, and kC6D6 = (9.9 ± 1.0) × 10?15 cm3 molecule?1 s?1, despite evidence that formation of a bound collision complex may contribute to the quenching mechanism. The roles of resonant energy transfer channels, Franck—Condon factors and the density of final states, in the quenching process, are discussed.  相似文献   

9.
The thermodynamic functions, C°p, S°, ?(F°?H°O)/T and (H°?H°O)/T, have been calculated in the ideal gas state at 1 atm for the following monohalogenated cycloalkanes: bromocyclopropane, bromocyclobutane, chlorocyclobutane, fluorocyclobutane, bromocyclopentane. The effect of pseudorotation of the cyclobutanes and bromocyclopentane on the thermodynamic function values was considered to be negligible.  相似文献   

10.
The efficiency of gas/wall vibrational energy transfer has been studied over the temperature range 800–1100 K by the variable encounter method. The average energies transferred per deactiviting collisions with the wall were determined at 800 K to be 3200 cm–1 and 2900 cm–1 for the 1,1,2,2-tetrafluorocyclobutane (TFCB) and 1-methyl-2,2,3,3-tetrafluorocyclobutane (MTFCB) molecules, respectively. This energy increased strongly with decreasing temperature. A comparison is made of with previous results for related molecules.  相似文献   

11.
A method has been developed, called the Variable Encounter Method, for the study of the relaxation of an initial vibrationally cold ensemble of molecules into a vibrationally hot distribution by a known and variable number of successive collisions with a hot wall. The theory of the experiment is presented. The system studied was the isomerization of 1,1-cyclopropane-d2 with a fused quartz wall temperature of 800 K to 1175 K, and average number of collisions from 2.3 to 22.3. Various modified gaussian and exponential models of energy transfer were found to give agreement with the data. The average down-step size was found to decline from ≤ 3500 cm?1 at the lowest temperature to ≈ 2500 cm? at the highest on the basis of a gaussian model. A mathematical analysis of the relation between mean first passage times and incubation times is given. Incubation times increase from ≈ 7 to ≈ 12 collisions with increasing temperature. Transient population distributions and the sequential reaction probabilities as a function of collision number are calculated.  相似文献   

12.
Cross sections for electron energy transfer from the initial rotational stateJ′of the two lowest vibrational levelsv′=0 andv′=1 of excited dimers Na2(A) to potassium atoms as described by Na2(A1Σ u + ,vJ′)+K(4S)→Na2 (X1Σ g + ,vJ″)+K(4P)+ΔE have been examined by laser-induced fluorescence. A strong increase of the cross section by as much as an order of magnitude has been observed for those dimervJ′-levels for which the dipole transitions are close to resonance of the 4S-4P transitions in the atom (ΔE<4 cm?1). The absolute cross sections for energy transfer have been calculated by the Rabitz approximation of first-order perturbation theory. In the case of closest energy resonance (ΔE=0.9 cm?1) the cross section is Q=7.8×10?13 cm2.  相似文献   

13.
Infrared fluorescence (IRF) from the CH stretch modes of vibrationally excited gas-phase azulene* was observed to depend on Evib according to a simple model. The IRF time/pressure behavior shows that the average energy transferred per collision depends strongly on Evib for azulene* + azulene and azulene* + argon collisions.  相似文献   

14.
The diffusion coefficient of O*2(1Δg) in O2(3Σ?g) has been measured as a function of pressure, D* = 0.201 ± 0.005 cm2 s?1 at 1 atmosphere and 298 K.  相似文献   

15.
The transition linewidth ΔE in crystal C6H6, C6D6 and sym-C6H3D3 has been measured as a function of temperature T from 4.2 to 135°K, and it extrapolates to a common value of ΔEo = 50 cm? at O°K. In C6H6 ΔE = (50 + 7T12) cm?1, indicative of strong exciton—phonon coupling, and there is a line shift of +40 cm?1 per substituent deuteron. Fluorescence excitation spectral data are used to separate the 1B1u(= S2) decay rate kH = 9.4 × 1012 sec?1, derived from ΔE0, into S2S1 internal conversion (rate ≈ 6.6 × 1012 sec?1) and S2Sx (channel 3) internal conversion (rate ≈ 2.8 × 1012 sec?1. A similar value of kH = 9.9 × 1012 sec?1 is obtained from the S2So fluorescence quantum yield of liquid benzene.  相似文献   

16.
The formation of complexes at pH 4.7 of the Hg(II) with five monothiosemicarbazone and two dithiosemicarbazone has been studied. The mercury(II) reacts with monothiosemicarbazones of salicylaldehyde (λmax = 363 nm, E = 1.69 × 104liters · mol?1cm?1), pi-colinadehyde (λmax = 363 nm, E = 2.38 × 104liters · mol?1cm?1), 6-methyl-picolinaldehyde (λmax = 363 nm, E = 2.28 × 104liters · mol?1cm?1), di-2-pyridylketone (λmax = 380 nm, E = 2.08 × 104liters · mol?1cm?1), and o-naphthoquinone (λmax = 540 nm, E = 1.03 × 104liters · mol?1cm?1) and with dithiosemicarbazones of 1,4-dihydroxyphthalimide (λmax = 430 nm, E = 2.56 × 104liters · mol?1cm?1) and dipyridylglyoxal (λmax = 363 nm, E = 2.37 × 104liters · mol?1cm?1). A critical comparison of the stoichiometry and apparent stability constant of complexes with mono- and dithiosemicarbazones is given.  相似文献   

17.
FeZrF6 exhibits a phase transition from the trigonal LiSbF6 structure type to the cubic high-temperature modification with an ordered ReO3 lattice at 212.3°K. From the temperature dependence of the quadrupole splitting in the temperature range 212°K ? T ? 4.1°K an axial splitting parameter |Δ1| = 68 cm?1 could be deduced, which is valid for T < 50°K and decreases linearly to 27 cm?1 (210°K) with increasing temperature. There is structural evidence supporting this interpretation and identifying the axial ligand field component as being of trigonal symmetry. Ligand field and EPR spectroscopic results, however, prove the existence of an additional dynamic Jahn-Teller coupling of tetragonal symmetry, which is obviously not seen by Mössbauer spectroscopy.  相似文献   

18.
In a molecular beam the effects of vibrational pumping of SF63 = 948 cm?1) are studied, using a line-tunable cw CO2 laser. Intracavity spontaneous Raman scattering is used for analysis. For excitation in the collision regime (xE/D ≤ 1), a thermal redistribution of the ν3 excitation over all vibrational modes is found, together with an average absorption up to six photons per molecule. The infrared absorption profile shows a red-shift of 6 cm?1. For excitation in the relatively rare collision regime (xE/D ? 4), a structured non-thermal ν1 Raman spectrum is observed, especially in the case of seeded molecular beams (10% in He). The observed hot-band peaks can be explained in terms of single-photon absorptions and collision-induced near-resonant V-V energy transfer, leading to single, double and triple excitations of the ν3 mode. The value of Trot in the beam is found to influence sensitively the non-resonant energy-transfer rate [e.g. hν3(948 cm?1)+ΔEroth4 + ν6)(962 cm?1) relative to the near-resonant transfer rate (hν3 + hν3 → 2hν3 + 3.5 cm?1)].  相似文献   

19.
IR and Raman Spectra of Matrix Isolated PSCl Gaseous PSCl is formed by the reaction of silver with PSCl3 at about 1100 K. After condensation in an argon gas matrix at 15 K, the three fundamentals of PSCl can be observed in the ir- and Ramanspectra: 716.1 cm?1 [ν(PS)]; 462.4 cm?1 [ν(PCl)]; 229 cm?1 [δ(SPCl)]. Experiments with 34S-enriched samples and a normal coordinate analysis show, that phosphorus is the central atom in this molecule and that the angle (SPCl) is approximately 110°.  相似文献   

20.
The absolute rate constant of the reaction between NH2 and ozone has been measured using a flash photolysis-laser resonance technique and found to be k4 = 6.3 (=1.0) × 10?14 cm3 molecule? s?1 at room temperature. The Arrhenius expression, determined from measurements in the temperature range 298–380 K is k4 = 4.2 × 10?12 exp(?2.5 = 0.5/RT) (E in kcal mole ?1. The possibility of formation or elimination of nitrogen oxides from the reactions of NH2 in the atmosphere is examined.  相似文献   

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