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1.
CCl2 free radicals were produced by a pulsed dc discharge of CCl4 in Ar. Ground electronic state CCl2(X) radicals were electronically excited to the A1B1 (0,4,0) vibronic state with an Nd:YAG laser pumped dye laser at 541.52 nm. Experimental quenching data of excited CCl2(A1B1 and a3B1) by O2, N2, NO, N2O, NH3, NH(CH3)2, NH(C2H5)2, and N(C2H5)3 molecules were obtained by observing the time‐resolved total fluorescence signal of the excited CCl2 radical in a cell, which showed a superposition of two exponential decay components under the presence of quencher. The quenching rate constants kA of CCl2(A) state and ka of CCl2(a) state were derived by analyzing the experimental data according to a proposed three‐level model to deal with the CCl2(X1A1, A1B1, a3B1) system. The formation cross sections of complexes of electronically excited CCl2 radicals with O2, N2, NO, N2O, NH3, and aminated molecules were calculated by means of a collision‐complex model. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 351–356, 2002 相似文献
2.
The Arrhenius parameters have been determined for the SO2(3B1) quenching reaction (9), SO2(3B1) + M → (SO2 ? M), for 21 different molecules as quenching partner M. The rate constants were calculated from phosphorescence lifetime measurements made over a range of reactant pressures and temperatures. Excitation of the SO2 (3B1) molecules was accomplished by two very different methods: (1) a 3829 Å laser pulse generated the triplet directly through absorption within the “forbidden” SO2 (3B1) → SO2 (1A1) band; (2) a broadband Xe-flash system generated SO2(3B1) molecules and triplets were formed subsequently by intersystem crossing, SO2(1B1) + M → SO2(3B1) + M. The measured rate constants were independent of the method of triplet formation employed. For the atmospheric gases, the activation energies (kcal/mole) were identical within the experimental error: N2, 2.9 ± 0.4; 02, 3.2 ± 0.5; Ar, 2.8 ± 0.6; CO2, 2.8 ± 0.4; CO, 2.7 ± 0.4; CH4, 2.5 ± 0.6. This energy corresponds to the first region of the SO2(3B1) → SO2(1A1) absorption spectra in which Brand and coworkers observe strong perturbations. It is suggested that the quenching in these cases results largely from the physical process involving potential energy surface crossing to another electronic state. Activation energies for SO2(3B1) quenching by the paraffinic hydrocarbons show a regular decrease in the series ethane, neopentane, propane, n-butane, cyclohexane, and isobutane, which parallels closely the decrease in C? H bond energies in these compounds. These and other data are most consistent with the dominance of chemical quenching in these cases. The rate constants for the olefinic and aromatic hydrocarbons and nitric oxide show only very small variations with temperature change, and they are near the kinetic collision number. These data support the hypothesis that quenching in these cases is associated with the formation of a charge-transfer complex and subsequent chemical interactions between the SO2(3B1) molecule and the π-system of these compounds. 相似文献
3.
Using the single-photon time correlation method, we have determined the lifetime of the S2(B3Σ?u) state from the decay rate of the fluorescence at 370 nm. A lifetime of 45.0 ± 0.6 ns was measured, and the cross section for fluorescence quenching by S2 as found to be 81.3 ± 4.7 A2. A slight dependence of the lifetime on the wavelength of the excitation source over the range of 280 to 337 nm was observed. 相似文献
4.
Resonance absorption of CO(A1Π → X1Σ+) fourth positive bands was used to excite CO molecules selectively into the ν′ = 0 and ν′ = 1 vibrational levels of the A1Π state. Studies of the fluorescence spectra at different added gas pressures yielded effective cross sections for the vibrational relaxation of A1Π, ν′ = 1 and for the quenching of A1π, ν′ = 0 molecules. Very large cross sections up to gas kinetic were measured for the rare gases He, Ne, Ar, and Kr as well as for the molecular species H2, D2 and N2 相似文献
5.
The reaction of trans-[Cr(Salen)(OH2)2]+ with aqueous sulfite yields trans-[Cr(Salen)(OH2)(OSO2(SINGLEBOND)O)]− (O-bonded isomer). The rate and activation parameter data for the formation of the sulfito complex are consistent with a mechanism involving rate-limiting addition of SO2 to the CrIII(SINGLEBOND)OH bond. The complex ions, trans-[(OH2)Cr(Salen)(OSO2(SINGLEBOND)O)]−, and trans-[(OH)Cr(Salen)(OSO2(SINGLEBOND)O)]2−, undergo reversible anation by NCS−, N3−, imidazole, and pyridine resulting in the formation of trans-[XCr(Salen)(OSO2(SINGLEBOND)O)](N+1)−(n=1 for X=N3−,NCS−, and 0 for X=imidazole and pyridine) predominantly via dissociative interchange mechanism. The labilizing action of the coordinated sulfite on the trans-CrIII-X bond in trans-[XCr(Salen)(OSO2)](n+1)− follows the sequence: NCS−pyridine ca. N3− ca. imidazole. Data analysis indicated that the coordinated sulfite has little trans activating influence. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 373–384, 1998 相似文献
6.
The chemical reactions of SO2(3B1) molecules with cis- and trans-2-butene have been studied in gaseous mixtures at 25°C by excitation of SO2 within the SO2(3B1) → SO2(+, 1A1) ‘forbidden’ band using 3500–4100-Å light. The initial quatum yields of olefin isomerization were determined as a function of the [SO2]/[2-butene] ratio and added gases, He and O2. The kinetic treatment of these data suggests that there is formed in the SO2(3B1) quenching step with either cis- or trans-2-butene, some common intermediate, probably a triplet addition complex between SO- and olefin. It decomposes very rapidly to form the 2-butene isomers in the ratio [trans-2-butene]/[cis-2-butene] = 1.8. In another series of experiments SO2 was excited using a 3630 ± 1-Å laser pulse of short duration, and the SO2(3B1) quenching rate constants with the 2-butenes were determined from the SO2(3B1) lifetime measurements. The rate constants at 21°C are (1.29 ± 0.18) × 1011 and (1.22 ± 0.15) × 1011 l/mole·sec with cis-2-butene and trans-2-butene, respectively, as the quencher molecule. Within the experimental error these quenching constants equal those derived from the quantum yield data. Thus the rate-determining step in the isomerization reaction is suggested to be the quenching reaction, presumably the formation of the triplet SO2-2-butene addition complex. In a third series of experiments using light scattering measurements, it was found that the aerosol formation probably originates largely from SO3 and H2SO4 mist formed following the reaction SO2(3B1) + SO2 → SO3 + SO(3Σ?). Aerosol formation from photochemically excited SO2-olefin interaction is probably unimportant in these systems and must be unimportant in the atmosphere. 相似文献
7.
Absolute emission cross sections have been determined for electron impact on CO, NO and N2. For the CO(A 1ΠX 1Σ+) and N2(a 1ΠX 1Σg) radiation our data is in good agreement with that of other groups. For CO+ (B2Σ+X2Σ+) the values of the emission cross sections are different from those measured previously. This discrepancy is explained in terms of an inadequate straylight correction in the former experiments. For the NO(A2Σ+X2Π) emission no previous σem values are known to the authors. Furthermore the electronic transition moments of the NO(A2Σ+X2Π) and CO+(B2ΣX2Σ+) systems have been measured and are found to be independent of the internuclear distance. 相似文献
8.
《Chemical physics letters》1985,122(4):361-364
Reaction rate constants of SiH2(X̄1A1) have been directly measured for the first time using the laser photolysis—laser-induced fluorescence method. The preparation of SiH2 radical in the laser photolysis (193 nm) of phenylsilane and the concentration of the radical is demonstrated by a dye laser at 580.1 nm (X̄1A1-Ā1B1). The reaction rate constants of SiH2(X̄1A1) with H2, CH4, C2H4, SiH4 and Si2H6, are 0.001, 0.01, 0.97, 1.1 and 5.7×10−10 cm3 molecule−1 s−1, respectively. For SiH2(Ā1B1(0.2,0)), the collision-free lifetime is 0.6 μs and the quenching rate constant for He is 3.8×10−10 cm3 molecule−1 s−1. 相似文献
9.
Z.-L. Cai 《Journal of computational chemistry》1994,15(3):346-350
The equilibrium geometries, excitation energies, force constants, and vibrational frequencies of the low-lying electronic states X2B1, 2A1, 2B2, and 2A2 of the PF2 radical have been calculated at the MRSDCI level with a double zeta plus polarization basis set. Our calculated geometry, force constants, and vibrational frequencies for the X2B1 state are in good agreement with experimental data. The electronic transition moments, oscillator strengths for the 2A1 → X2B1 and 2A2 → X2B1 transitions, and radiative lifetimes for the 2A1 and 2A2 states are calculated based on the MRSDCI wave functions. © 1994 by John Wiley & Sons, Inc. 相似文献
10.
Time-resolved investigations of the atomic resonance fluorescence Sr(53P1 → 51S0) and the molecular chemiluminescence from SrCl(A2Π1/2,3/2, B2Σ+ → X2Σ+) are reported following the reaction of the electronically excited strontium atom, Sr(5s5p(3PJ)), 1.807 eV above its 5s2(1S0) electronic ground state, with CH2Cl2. The optically metastable strontium atom was generated by pulsed dye-laser excitation of ground state strontium vapor to the Sr(53P1) state at λ = 689.3 nm (Sr(53P1 ← 51S0)) at elevated temperature (850 K) in the presence of excess helium buffer gas in which rapid Boltzmann equilibration within the 53PJ manifold takes place. Sr(53PJ) was then monitored by time-resolved atomic fluorescence from Sr(53P1) at the resonance wavelength together with chemiluminescence from electronically excited SrCl resulting from reaction of the excited atom with CH2Cl2. The molecular systems recorded in the time-domain were SrCl(A2Π1/2 → X2Σ+) (Δν = 0, λ = 674 nm), SrCl(A2Π3/2 → X2Σ+) (Δν = 0, λ = 660 nm), and SrCl(B2Σ+ → X2Σ+) (Δν = 0, λ = 636 nm). Both the A2Π (179.0 kJ mol?1) and (B2Σ+(188.0) kJ mol?1) states of SrCl are energetically accessible on collision between Sr(3P) and CH2Cl2. Exponential decay profiles for both the atomic and molecular (A,B – X) chemiluminescence emission are observed and the first-order decay coefficients characterized in each case. These are found to be equal under identical conditions and hence SrCl(A2Π, B2Σ+) are shown to arise from direct Cl-atom abstractions on reaction with this halogenated species. The combination of integrated molecular and atomic intensity measurements, coupled with optical sensitivity calibration, yields estimations of the branching ratios into the A1/2,3/2, B, and X states arising from Sr(53 PJ) + CH2Cl2 which are found to be as follows: A1/2, 3.0 × 10?3; A3/2, 1.7 × 10?3; B, 4.4 × 10?4 yielding ΣSrCl(A1/2 + A3/2 + B) = 5.1 × 10?3. As only the X, A and B states of SrCl are accessible on reaction, this indicates an upper limit for the branching ratio into the ground state of 0.995. The present results are compared with previous time-resolved measurements on SrF, Cl, Br(A2Π,B2Σ+ ? X2Σ+) that we have reported on various halogenated species and with analogous chemiluminescence studies on Sr(3P) with other halides obtained from molecular beam measurements. The results are further compared with those from a series of previous analogous investigations in the time-domain we have presented of molecular emissions from CaF, Cl, Br, I (A,B – X) arising from the collisions of Ca(43PJ) with appropriate halides and with branching ratio data for Ca(43PJ) obtained in beam measurements. © 1995 John Wiley & Sons, Inc. 相似文献
11.
用激光光解-激光诱导荧光方法研究了室温下(T=293 K) HCF(X~1A’)自由基与SO2分子的反应动力学. 实验中HCF(X~1A’)自由基是由213 nm激光光解HCFBr2产生的, 用激光诱导荧光(LIF)检测HCF(X~1A’)自由基的相对浓度随着反应时间的变化, 得到此反应的二级反应速率常数为: k=(1.81±0.15)×10-12 cm38226;molecule-18226;s-1, 体系总压为1862 Pa. 高精度理论计算表明, HCF(X~1A’)和SO2分子反应的机理是典型的加成-消除反应. 我们运用RRKM-TST理论计算了此二级反应速率常数的温度效应和压力效应, 计算结果和室温下测定的二级反应速率常数符合得较好. 相似文献
12.
Masaharu Tsuji Chikashi Yamagiwa Minoru Endoh Yukio Nishimura 《Chemical physics letters》1980,73(3):407-412
The extensive bands observed from the helium afterglow reaction of SO2 in the 250–540 nm region are assigned to the new SO+(A2Π-X2Πr) system produced from the He+/SO2 dissociative charge-transfer reaction at thermal energy. They had been erroneously interpreted as the SO+2 (C?-X?) system produced from He(23S)/SO2 Penning ionization. The spectroscopic constants for the SO+A2Π) and SO+(X2Πr) states were determined. 相似文献
13.
Summary Full configuration interaction (FCI) geometry optimizations have been performed for the X3B1, a1A1, b1B1 and c1A1 electronic states of CH2, the X2B1 and A2A1 electronic states of NH2 and the X1A1 electronic state of BH3 using a DZP basis set. The results are compared with those obtained using the MRD-CI method at different levels of theoretical treatment. The agreement between the geometrical parameters optimized with the FCI and MRD-CI methods is very good. 相似文献
14.
《Chemical physics letters》1985,119(4):327-330
The photoabsorption cross sections for H2S were measured in the 47–102 nm region using synchrotron radiation. The absorption cross section in the range of λ > 90 nm showed many small peaks assigned to the 5a1 → 6sa1 Rydberg transition. and in the 77–90 nm region the 2b2 → nda1 (n = 4.5) Rydberg series were observed. At the energies of 18.2. 19.5 and 21.1 eV, small broad peaks were recognized and tentatively assigned to the vertical ionization potentials of the 14A2, 4B1 and 24A2 electronic states of the H2S+ ion, respectively, by comparing with the recent ab initio calculations for the H2S+ energy diagram. 相似文献
15.
Z.-L. Cai 《International journal of quantum chemistry》1993,45(3):295-301
The equilibrium geometries, excitation energies, force constants, and vibrational frequencies for four low-lying electronic states X 2A1, 2B1, 2B2, and 2A2 of the BF2 radical have been calculated at the MRSDCI level with a double zeta plus polarization basis set. Our calculated excitation energy for X2A1 → 2B1 is in agreement with available experimental data. The electronic transition dipole moments, oscillator strengths for the 2B1 → X2A1 and 2B2 → X2A1 transitions, radiative lifetimes for the 2B1 and 2B2 states, and the spin properties for the X2A1 state are calculated based on the MRSDCI wave functions, predicting results in reasonable agreement with available experimental data. © 1993 John Wiley & Sons, Inc. 相似文献
16.
《Chemical physics letters》1987,136(6):501-505
The rate coefficients for the quenching of NO(A 2Σ, v' =0) by NO, N2O, H2O, O2, SF6 and CO2 were measured to be (in units of 10−10 cm3 molecule−1 s−1): 2.67±0.41, 3.79±0.49, 7.8±1.0, 1.46±0.25, 3.82±0.49, and 4.30±0.26, respectively. Upper limits for the quenching rate constants by N3, Ar, Ne, H2, and CF4 were also measured. All experiments were carried out by monitoring the temporal profiles of A 2Σ, v' =O→X2Π, v″=3 fluorescence after 226 nm pulsed laser excitation of NO(X2Π) to NO(A2Σ,v'=0). 相似文献
17.
Susan M. Burnett Amy E. Stevens C.S. Feigerle W.C. Lineberger 《Chemical physics letters》1983,100(2):124-128
Photoelectron spectra of the vinylidene anion (C2H2?) show vibrational structure in X1A1 vinylidene up 12 kcal/ mol above the vibrational ground state. Analysis yields an EA(C2H21 A1) of 0.47 ± 0.02 eV, and frequencies for the CC stretch and HCH bend. Absence of the 3B2 state in the photoelectron spectra indicates the 1A1-3B2 splitting in vinylidene is ? 1.7 eV. 相似文献
18.
Decomposition studies of trichlorosilane, dichlorosilane, and monochlorosilane at 921 K, 872 K, and 806 K, respectively, are reported. The studies were made at fixed reactant pressures over a range of total pressures in a wall conditioned, quartz reactor connected to a quadrupole mass-spectrometer. Products were monitored sequentially and continuously in time. The dichlorosilane decomposition was also studied by the comparative-rate single-pulse shock-tube method at temperatures around 1250 K. Two mechanisms of decomposition are considered: a silylene based mechanism initiated by molecular elimination reactions (Scheme I), and a free radical based mechanism initiated by bond fission reactions (Scheme V). Modeling tests of these mechanisms show that only the former is consistent with the experimental data. The decompositions are shown to be essentially nonchain processes initiated by the following pressure dependent reactions: HSiCl3(SINGLEBOND)4→ SiCl2+HCl, H2SiCl2(SINGLEBOND)1→ SiCl2+H2 and H3SiCl(SINGLEBOND)5→ HSiCl+H2. High pressure Arrhenius parameters recommended for these reactions are A4,∞=A1,∞=A5,∞=1014.5±0.5 s−1, E4,∞=71.9±2.1 kcal/mol, E1,∞=69.2±2.0 kcal/mol, and E5,∞=60.6±1.8 kcal/mol. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 69–88, 1998. 相似文献
19.
Wen‐Zuo Li Jian‐Bo Cheng Qing‐Zhong Li Bao‐An Gong Jia‐Zhong Sun 《International journal of quantum chemistry》2010,110(14):2683-2688
Geometries, frequencies, and energies of the 12B1, 12A2, 12B2, 22B1, 22B2, and 12A1, of the C6H5Br+ ion were calculated by using CASSCF and CASPT2 methods in conjunction with an ANO‐RCC basis. The CASPT2//CASSCF adiabatic excitation energies and CASPT2 relative energies for the six states are in good agreement with experiment. The X, A, B, C, and D electronic states of the C6H5Br+ ion were assigned to be X2B1, A2A2, B2B2, C2B1, and D2B2 based on the CASSCF and CASPT2 calculations. The assignment on the D state of the C6H5Br+ ion is different from the previously published works. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 相似文献
20.
Junxia Cheng Hong Zhang Xinlu Cheng Shenjiang Wu 《International journal of quantum chemistry》2019,119(24):e26027
The laser synthesis of alkaline earth dimers (Be2, Mg2, Ca2, Sr2, and Ba2) is investigated by theoretical calculation. Photoassociation based on ab initio calculations is rationalized by Franck-Condon filtering. The optimal target states of photoassociations have been obtained, which are A1∑+u state for Be2, Mg2, and Ca2, and are B1∑+u state for Sr2 and Ba2, corresponding to vibrational transition bands from X1∑+g to excited state are 0-1, 0-7, 0-10, 0-13, and 0-3, respectively. The proposed laser drive transitions to target states are also investigated that range from 350 to 740 nm. By using quantum wave-packet dynamic methods, we calculated the absorption cross sections of photon energy and yields for the selected states of photoassociation. It show that the most sensitive molecules for quantum selective control of photoassociation are Be2 and Ba2 for alkaline earth dimers. These important parameters will provide a feasible scheme for further experimental researches. 相似文献