高振动激发态吡嗪碰撞传能的QCT计算研究

用准经典轨线(QCT)方法计算了高振动激发态吡嗪(C4N2H4)与N2、O2、NH3、基态吡嗪之间的碰撞传能. C4N2H4通过计算发现, 高振动激发态C4N2H4与N2、O2碰撞发生的主要是V-V传能, 与NH3碰撞发生的主要是V-R传能, 与基态C4N2H4碰撞发生的主要是V-V(R)传能. 通过比较高振动激发态C4N2H4、C6F6、C6H6与其基态分子的碰撞传能， 发现此类碰撞传能中, 若分子的对称性高， 则V-V传能更容易实现.     

烷烃和胺类分子对电子激发态CH(A~2Δ和B~2Σ~-)自由基猝灭

用266nm激光光解CHBr_3分子产生CH(A,B)态自由基,通过测量CH(A,B→X)自发辐射的时间分辨信号测定室温下(CH_3)_2NH、(C_2H_5)_2NH、(C_2H_5)_3N、n-C_5H_(12)、n-C_6H_(14)和n-C_7H_(16)对CH(A,B,v'=0)的猝灭速率常数.发现猝灭速率常数与猝灭剂烷烃分子中的C-H键数近似成线性关系,但对大的烷烃分子,这种增加逐渐趋缓.用碰撞络合物模型计算胺类分子及烷烃分子与CH形成碰撞络合物时的生成截面,结果表明,在电子激发态CH自由基的猝灭过程中,碰撞对子间的多极相互吸引势和色散力作用势可能起重要作用.     

碘乙烷激光裂解反应通道及产物的能量分布

用分子束和飞行时间技术测量了248 nm激光光解过程C_2H_5I→C_2H_5+I°(~2p_(1/2))和C_2H_5I→C_2H_5+I(~2p_(3/2))裂解碎片的平动能和内能分布。测得通道比I~*/I为2.37。根据实验结果, 对光解过程中电子激发态特性, 产生I(~2p_(3/2))通道的机理以及乙基自由基的振动激发作了讨论。     

NH2(A2A1,090,423)的电子猝灭和转动态-态传能

在束 气和束 束实验条件下,详细研究了NH2(A1,090,423)自由基分别与Ar,N2,O2和NH3碰撞引起的电子态猝灭和转动态 态传能,获得了总的猝灭截面σQ (分别为≤0.17、0.26、0.30和0.48 nm2),以及相对转动态 态传能截面.利用碰撞络合物模型计算的电子猝灭截面与实验测得的截面具有基本相同的趋势,表明长程吸引势在猝灭过程中起着重要的作用.同时还发现,转动态 态传能中相对截面随着碰撞对的折合质量的减小而下降.由于NH3具有较大的偶极矩以及O2的开壳层电子结构使得猝灭截面增大,而转动态 态传能截面减小.     

NH_2(~2A_1,090,4_(23))的电子猝灭和转动态-态传能

在束-气和束-束实验条件下,详细研究了NH_2(~2A_1,090,4_(23))自由基分别与 Ar,N2,O2和 NH3碰撞引起的电子态猝灭和转动态-态传能,获得了总的猝灭截面σQ (分别为≤ 0.17、 0.26、 0.30和 0.48 nm~2),以及相对转动态-态传能截面 .利用碰撞络合物模型计算的电子猝灭截面与实验测得的截面具有基本相同的趋势,表明长程吸引势在猝灭过程中起着重要的作用 .同时还发现,转动态-态传能中相对截面随着碰撞对的折合质量的减小而下降 .由于 NH_3具有较大的偶极矩以及 O_2的开壳层电子结构使得猝灭截面增大,而转动态-态传能截面减小 .     

NH2(A~2A1, 090,423)的电子猝灭和转动态-态传能

在束-气和束-束实验条件下,详细研究了NH2(A2A1,090,423)自由基分别与Ar,N2,O2和NH3碰撞引起的电子态猝灭和转动态-态传能,获得了总的猝灭截面σQ(分别为≤0.17、0.26、0.30和0.48 nm2),以及相对转动态-态传能截面.利用碰撞络合物模型计算的电子猝灭截面与实验测得的截面具有基本相同的趋势,表明长程吸引势在猝灭过程中起着重要的作用.同时还发现,转动态-态传能中相对截面随着碰撞对的折合质量的减小而下降.由于NH3具有较大的偶极矩以及O2的开壳层电子结构使得猝灭截面增大,而转动态-态传能截面减小.     

分子单重/叁重混合激发态碰撞传能中的量子干涉效应

量子干涉效应是基于量子力学波粒二象性原理,即微观粒子的运动皆具有波的特性而产生的一种干涉现象,故又称为物质波干涉.近年来,在分子的光激发、光解和光电离及碰撞过程中皆已观察到量子干涉效应,成为分子动态学领域研究热点之一.我们小组在国际上首次得到了单重/叁重混合激发态分子碰撞传能中的量子干涉的实验证据,从理论上导出了包括干涉相位角的传能截面公式,从实验上发展了激光双共振多光子电离光谱技术,用以测定了CO(A1П,v=0/e3∑-,v=1)与各种原子(He,Ne,Ar)及双原子分子H2,O2,N2,HCl碰撞传能的干涉角.其后又与李丽的小组合作,在热管炉中用激光双共振诱导荧光法观察到Na2(A1∑+uv=8/b3П0u,v=14)-Na碰撞中的量子干涉效应,证明了碰撞干涉效应的普遍性.近年来,在理论方面,我们发展了基于含时微扰的一级波恩近似量子散射方法,计算出了上述碰撞体系的干涉角θST,与实验值符合极好.本文指出虽然气池实验测得的干涉角θST是不同分子碰撞速度及碰撞参数的"平均"结果,但与理论计算的微分干涉角尚比较接近,可提供激发态分子碰撞相互作用势的重要而难得的信息.     

CO(υ)高振动激发态向C2H2的振动传能研究

用时间分辨富里叶红外发射谱研究了高振动激发态ＣＯ向Ｃ２Ｈ２的传能，得到了ＣＯ（ｖ＝１－３）各振动态布居及其随时间的变化。利用微分法解出弛豫微分方程组，获得ＣＯ（ｖ＝１－３）向Ｃ２Ｈ２的传能速率常数分别为：２．０±０．１，６．０±０．２和９．４±０．８（１０＾－１３ｃｍ＾３·ｍｏｌｅｃｕｌｅ＾－１·ｓ＾－１）。传能速率随着振动量子数的增加而迅速增加。ＣＯ的振动能应向Ｃ２Ｈ２的对称伸缩模ｖ２近共振Ｖ－     

CH(A^2△和B^2∑^-)和醇类分子碰撞过程动力学研究

本文报道用四倍频YAG激光(266nm)光解CHBr_3产生电子激发态CH(A,B)自由基和测量自发辐射CH(A,B→X)的时间分辨信号的方法测定了室温(290K)下 CH(A,B)被醇类分子(乙醇、异丙醇、正丁醇、异戊醇和叔戊醇)猝灭的速率常数,实验测定的CH(A)和 CH(B)猝灭速率常数K_q~A和K_q~B(单位为10~(-10)cm~3·molecule~(-1)·s~(-1))值如下(误差为线性拟合的标准偏差):此外,还从碰撞配合物模型出发,就醇分子中OH基对猝灭速率常数的影响作了讨论.     

DMF-H_2O缔合体系的~1HNMR研究

DMF水溶液是一种生物分子水溶液的简单生化模型。测量了DMF-H_2O体系不同 温度下全浓度范围的~1H NMR数据，对体系中的缔合情况进行了讨论，基于H_2O, H_2O·DMF, (H_2O)_2和(DMF)_2·H_2O的缔合平衡建立了化学缔合模型，采用最 小二乘法拟合实验数据，联合遗传算法和Levenberg-Marquardt算法对模型参数进 行全局寻优求解得不同温度的缔合平衡常数K，再根据不同温度的K求得缔合平衡的 ΔH和ΔS。为了更好地理解DMF水溶液中分子间的相互作用，还测量了298 K下DMF- CCl_4和DMF-BuOH体系全浓度范围的~1H NMR数据作为比较，结合NMR的基本原理对 各DMF溶液体系~1H NMR的实验现象进行了分析和解释，认为水溶液的特殊结构、氢 键和DMF酰胺基的共轭体系是影响DMF-H_2O体系~1H NMR的主要因素。     

Spin-orbit coupling in O2(upsilon)+O2 collisions: I. Electronic structure calculations on dimer states involving the X 3Sigmag-, a 1Deltag, and b 1Sigmag+ states of O2

The importance of vibrational-to-electronic (V-E) energy transfer mediated by spin-orbit coupling in the collisional removal of O2(X 3Sigmag-,upsilon>or=26) by O2 has been reported in a recent communication [F. Dayou, J. Campos-Martinez, M. I. Hernandez, and R. Hernandez-Lamoneda, J. Chem. Phys. 120, 10355 (2004)]. The present work provides details on the electronic properties of the dimer (O2)2 relevant to the self-relaxation of O2(X 3Sigmag-,upsilon>0) where V-E energy transfer involving the O2(a 1Deltag) and O2(b 1Sigmag+) states is incorporated. Two-dimensional electronic structure calculations based on highly correlated ab initio methods have been carried out for the potential-energy and spin-orbit coupling surfaces associated with the ground singlet and two low-lying excited triplet states of the dimer dissociating into O2(X 3Sigmag-)+O2(X 3Sigmag-), O2(a 1Deltag)+O2(X 3Sigmag-), and O2(b 1Sigmag+)+O2(X 3Sigmag-). The resulting interaction potentials for the two excited triplet states display very similar features along the intermolecular separation, whereas differences arise with the ground singlet state for which the spin-exchange interaction produces a shorter equilibrium distance and higher binding energy. The vibrational dependence is qualitatively similar for the three studied interaction potentials. The spin-orbit coupling between the ground and second excited states is already nonzero in the O2+O2 dissociation limit and keeps its asymptotic value up to relatively short intermolecular separations, where the coupling increases for intramolecular distances close to the equilibrium of the isolated diatom. On the other hand, state mixing between the two excited triplet states leads to a noticeable collision-induced spin-orbit coupling between the ground and first excited states. The results are discussed in terms of specific features of the dimer electronic structure (including a simple four-electron model) and compared with existing theoretical and experimental data. This work gives theoretical insight into the origin of electronic energy-transfer mechanisms in O2+O2 collisions.     

Theoretical and experimental studies of collision-induced electronic energy transfer from v=0-3 of the E(0g +) ion-pair state of Br2: collisions with He and Ar

Collisions of Br(2), prepared in the E(0(g)+) ion-pair (IP) electronic state, with He or Ar result in electronic energy transfer to the D, D', and beta IP states. These events have been examined in experimental and theoretical investigations. Experimentally, analysis of the wavelength resolved emission spectra reveals the distribution of population in the vibrational levels of the final electronic states and the relative efficiencies of He and Ar collisions in promoting a specific electronic energy transfer channel. Theoretically, semiempirical rare gas-Br(2) potential energy surfaces and diabatic couplings are used in quantum scattering calculations of the state-to-state rate constants for electronic energy transfer and distributions of population in the final electronic state vibrational levels. Agreement between theory and experiment is excellent. Comparison of the results with those obtained for similar processes in the IP excited I(2) molecule points to the general importance of Franck-Condon effects in determining vibrational populations, although this effect is more important for He collisions than for Ar collisions.     

Quantum-mechanical calculations on pressure and temperature dependence of three-body recombination reactions: application to ozone formation rates

A quantum-mechanical model is designed for the calculation of termolecular association reaction rate coefficients in the low-pressure fall-off regime. The dynamics is set up within the energy transfer mechanism and the kinetic scheme is the steady-state approximation. We applied this model to the formation of ozone O + O2 + M --> O3 + M for M = Ar, making use of semiquantitative potential energy surfaces. The stabilization process is treated by means of the vibrational close-coupling infinite order sudden scattering theory. Major approximations include the neglect of the O3 vibrational bending mode and rovibrational couplings. We calculated individual isotope-specific rate constants and rate constant ratios over the temperature range 10-1000 K and the pressure fall-off region 10(-7)-10(2) bar. The present results show a qualitative and semiquantitative agreement with available experiments, particularly in the temperature region of atmospheric interest.     

Electronic to vibrational energy transfer assisted by interacting transition dipole moments: a quantum model for the nonadiabatic I2(E) + CF4 collisions

We report a theoretical study of nonadiabatic transitions within the first-tier ion-pair states of molecular iodine induced by collisions with CF(4). We propose a model that treats the partner as a spherical particle with internal vibrational structure. Potential energy surfaces and nonadiabatic matrix elements for the I(2)-CF(4) system are evaluated using the diatomics-in-molecule perturbation theory. A special form of the intermolecular perturbation theory for quasi-degenerate electronic states is implemented to evaluate the corrections to the long-range interaction of transition dipole moments of colliding molecules. The collision dynamics is studied by using an approximate quantum scattering approach that takes into account the coupling of electronic and vibrational degrees of freedom. Comparison with available experimental data on the rate constants and product state distributions demonstrates a good performance of the model. The interaction of the transition dipole moments is shown to induce very efficient excitation of the dipole-allowed upsilon(3) and upsilon(4) modes of the CF(4) partner. These transitions proceed predominantly through the near-resonant E-V energy transfer. The resonant character of the partner's excitation and the large mismatch in vibrational frequencies allow one to deduce the partner's vibrational product state distributions from the distributions measured for the molecule. The perspectives of the proposed theoretical model for treating a broad range of molecular collisions involving the spherical top partners are discussed.     

Cross sections and rate constants for the C(3P)+OH(X 2Pi)-->CO(X 1Sigma+)+H(2S) reaction using a quasiclassical trajectory method

First quasiclassical trajectory calculations have been carried out for the C(3P)+OH(X 2Pi)-->CO(X 1Sigma+)+H(2S) reaction using a recent ab initio potential energy surface for the ground electronic state, X 2A', of HCO/COH. Total and state-specific integral cross sections have been determined for a wide range of collision energies (0.001-1 eV). Then, thermal and state-specific rate constants have been calculated in the 1-500 K temperature range. The thermal rate constant varies from 1.78x10(-10) cm3 s-1 at 1 K down to 5.96x10(-11) cm3 s-1 at 500 K with a maximum value of 3.39x10(-10) cm3 s-1 obtained at 7 K. Cross sections and rate constants are found to be almost independent of the rovibrational state of OH.     

Franck-Condon effects in collision-induced electronic energy transfer: I2(E; v = 1,2) + He, Ar

Collisions of I2 in the E electronic state with rare gas atoms result in electronic energy transfer to the D, beta, and D' ion-pair electronic states. Rate constants for each of these channels have been measured when I2 is initially prepared in the J = 55, nu = 1 and 2 levels in the E state. The rate constants and effective hard sphere collision cross sections confirm the trends observed when nu = 0 in the E state is initially prepared: He collisions favor population of the D state, while Ar collisions favor population of the beta state. Final state vibrational level distributions are determined by spectral simulation and are found to be qualitatively consistent with the trends in the Franck-Condon factors. The experimental distributions are also compared to the recent quantum scattering calculations of Tscherbul and Buchachenko.     

A new ab initio potential energy surface for studying vibrational relaxation in NO(v) + NO collisions

A new ab initio potential energy surface for the ground state of the NO-NO system has been calculated within a reduced dimensionality model. We find an unusually large vibrational dependence of the interaction potential which explains previous spectroscopic observations. The potential can be used to model vibrational energy transfer, and here we perform quantum scattering calculations of the vibrational relaxation of NO(v). We show that the vibrational relaxation for v = 1 is 4 orders of magnitude larger than that for the related O(2)(v) + O(2) system without having to invoke nonadiabatic mechanisms as had been suggested in the past. For highly vibrationally excited states, we predict a strong dependence of the rates on the vibrational quantum number as has been observed experimentally, although there remain important quantitative differences. The importance of a chemically bound isomer on the relaxation mechanism is analyzed, and we conclude it does not play a role for the values of v considered in the experiment. Finally, the intriguing negative temperature dependence of the vibrational relaxation rate constants observed in experiments was studied using an statistical model to include the presence of many asymptotically degenerate spin-orbit states.     

Rovibrational resonance effects in collision-induced electronic energy transfer: I2(E,v=0-2)+CF4

Collisions of I2 in the E(0(g)+) electronic state with CF4 molecules induce electronic energy transfer to the nearby D, beta, and D' ion-pair states. Simulations of dispersed fluorescence spectra reveal collision-induced electronic energy transfer rate constants and final vibrational state distributions within each final electronic state. In comparison with earlier reports on I2(upsilon(E)=0-2) collisions with He or Ar atoms, we find markedly different dynamics when I2, excited to the same rovibronic states, collides with CF4. Final vibrational state distributions agree with the associated Franck-Condon factors with the initially prepared state to a greater degree than those found with He or Ar collision partners and suggest that internal degrees of freedom in the CF4 molecule represent a substantial means for accepting the accompanying loss of I2 vibronic energy. Comparison of the E-->D transfer of I2 excited to the J=23 and J=55 levels of the upsilon(E)=0 state reveals the onset of specific, nonstatistical dynamics as the available energy is increased above the threshold for excitation of the low frequency nu2 bending mode of CF4.