【作者】 赵增霞；

【导师】 孙家钟； 张红星；

【作者基本信息】 吉林大学 ， 物理化学， 2008， 博士

【摘要】 本文利用从头算和密度泛函直接动力学方法研究了RCN（CH₃, C₂H₅, C₃H₇）参与的重要化学反应的微观机理和速率常数。使用全活化空间自洽场（CASSCF）方法,对HCCN、XCCN（X=F, Cl和Br）及其阴阳离子激发态性质进行了深入研究。主要内容概括如下:1.使用MC-QCISD//BH&H-LYP和MC-QCISD//MP2方法,研究氢提取反应C₂H + CH₃CN→products （R1）, C₂H + CH₃CH2CN→products （R2）,和C₂H + CH₃CH2CH2CN→products （R3）。得到了上述反应的反应路径、反应势垒、反应焓及变分过渡态理论速率常数。在实验温度范围内,理论计算的速率常数与最近的实验值符合得较好,说明了理论结果的可靠性。并在实验所没有测量的一些温度范围内,给出可靠的理论预测结果。对于多通道反应R2和R3,到目前为止实验上还没有给出反应分支比的信息。本文通过理论计算得到了这些反应的分支比。有助于更好地理解这类反应的微观机理,为进一步实验研究提供理论线索。通过研究CH₃CN, CH₃CH2CN,和CH₃CH2CH2CN与C₂H反应的速率常数,得到如下的反应活性规律: k（CH₃CH2CH2CN） > k（CH₃CH2CN） > k（CH₃CN）。2.使用CASPT2//CASSCF理论方法,在Cs对称性下和aug-cc-pVTZ基组水平下,研究和表征了HCCN自由基及其阴阳离子的基态和激发态性质,计算了分子几何、谐振频率、绝热激发能以及跃迁强度。在优化得到的氰基卡宾HCCN自由基基态几何构型下,计算了HCCN的垂直激发能。计算得到的HCCN的X³A″→2³A″, X³A″→³A′, X³A″→3³A″, X³A″→2³A′,和X³A″→3³A′垂直激发能分别为4.179, 4.395, 4.579,4.727和5.506 eV。HCCN的单-三重态的劈裂能为0.738 eV。在CASPT2//CASSCF理论水平下,计算得到垂直和绝热的电离能,详细地解释了HCCN自由基和HCCN-阴离子的光电子谱（PES）。计算所得结果与实验值符合得很好。3.在Cs对称性和ANO-S基组下,使用全活化空间自洽场方法（CASSCF）,研究了卤代氰基卡宾自由基XCCN（X = F, Cl和Br）及其阴离子的低能电子激发态性质。为进一步考虑动态电子相关效应,采用多组态二级微扰理论（CASPT2）获得更加精确的能量值.结果表明XCCN的基态是三重态。单重态和三重态的能隙差ΔES-T（kJ/mol）: FCCN（7.4） < ClCCN（13.4） < BrCCN（16.6）。计算得到XCCN（X = F, Cl和Br）最低垂直激发能分别为408.3,385.4和345.2 kJ/mol,归因于π（a′）→nz的电子跃迁。计算得到XCCN的电子亲和势分别为235.7, 233.0,和237.2 kJ/mol,与HCCN相比,电子亲合势变大。更多还原

【Abstract】 The small molecules and radicals including N atom have received much attention as important as the important components of atmosphere and Titan’s atmosphere. These molecules and radicals participate in many photochemistry and photophysical reactions. As a result, quantum chemical investigations on the excited states of several important free radicals containing N atom. In this thesis ab initio and density functional theory （BH&HLYP） combined with the direct dynamics methods have been used to study the reactions C₂H + RCN （R = CH₃, C₂H₅, and C₃H₇）; CASPT2//CASSCF calculations were performed to investigated the XCCN （X = H, F, Cl, and Br ） radicals. The main results are summarized as followed:1. Ab initio and density functional theory direct dynamics methods have been used to take a systematic theoretical study on the following hydrogen abstraction reactions: C₂H + CH₃CN→products （R1）, C₂H + CH₃CH2CN→products （R2）, C₂H + CH₃CH2CH2CN→products （R3）. The main object is to provide accurate results for the reaction path and the temperature dependence relation of rate constants, in order to explore the reaction mechanism of these reactions. By means of the Gaussian 98 program, at the BH&HLYP level, the geometries and frequencies of the stationary points （reactant, transition state, and product） were calculated. The minimum energy path （MEP） was calculated at the same level by intrinsic reaction coordinate （IRC） theory. Furthermore, selected points along the MEP, the force constant matrices as well as the harmonic vibrational frequencies were obtained. In order to gain more accurate information of energy, the energies of the selected points on the MEP were refined at MC-QCISD//BH&HLYP level. By POLYRATE-Version 8.4.1 program, the conventional transition state theory （TST） and canonical variational transition state theory with small-curvature tunneling correction （CVT/SCT） were applied to obtain the reaction rate constants. The main results show that : （1） The study on the reaction R1, R2, and R3 indicates that the BH&HLYP/6-311G（d,p） level of theory can give the accurate geometries and frequencies, which are in good agreement with the results by MP2/6-311G（d,p） level. The single point energy calculated at the MC-QCISD//BH&HLYP level can provide more accurate information on energy of the reaction path. This is indispensable to calculate accurately of the reaction rate constants. The CVT/SCT rate constants calculated at the MC-QCISD//BH&HLYP level are in good agreement with the experimental values. The results of this study show that the dual-level DFT direct dynamics method is appropriated for the theoretical study on the hydrogen abstraction reactions for R1, R2, and R3. （2） In the reactions C₂H + RCN（R=CH₃, C₂H₅, C₃H₇）, for the hydrogen abstraction reactions, the values of classical barrier heights decrease in the order CH₃CN > C₂H₅CN > C₃H₇CN. （3） For reaction R2, theα-hydrogen abstraction channel andβ-hydrogen abstraction channel are competitive over the temperature range 104-2000K. For reaction R3, theγ-hydrogen abstraction channel is preferred at lower temperatures, while the contribution ofβ-hydrogen abstraction will become more significant with a temperature increase. The branching ratio to theα-hydrogen abstraction channel is found negligible over the whole temperature range.2. The present work investigated the ground state and low-lying excited states of cyanocarbene HCCN, its anion HCCN-, and cation HCCN+, and by using the CASPT2//CASSCF level with aug-cc-pVTZ basis set. The electronic configurations are used to explain the geometrical alteration in detail. We have presented results from a fully correlated ab initio investigation of the electronic spectrum of HCCN neutral radical by means of using the CASPT2 method, a well-established procedure for accurate calculations of electronic spectra of molecules. The five low-lying triplet valence excited states （2³A″, 3³A″, ³A′, 2³A′and 3³A′） located at 4.179, 4.395, 4.579, 4.727, and 5.056 eV with significant oscillator strength. Among the allowed transitions the energy of X³A″→2³A″is the lowest, which is the Based on the corresponding results, the PES of the HCCN radical andHCCN- anion are assigned. The vertical and adiabatic ionization energies assigned to six ionic states at the CASPT2 level. The computed first VIP and AIP are 10.652 eV and 10.513 eV, respectively.The vertical detachment energy VDE in a wide range of 2.210- 7.399 eV is assigned to a total 12 neutral states at the CASPT2 level. The ten detachment energies are also confirmed at the CASPT2 level adiabatically. For the PES of anion, the first VDE and ADE calculated are 1.568 eV and 1.768 eV, which are comparable with the experimental data of 2.003±0.014eV. The calculated VDE and ADE of the 1A′state are 2.305 eV and 2.507 eV, respectively, which agree well with the ADE values of 2.518±0.008 eV in the experiment.3. Complete active space self-consistent field method （CASSCF） calculations with ANO-S basis sets were performed for the ground and low-lying electronic excited states of halocyanocarbene XCCN and their anions, with X = F, Cl, and Br. Our results show that the XCCN have triplet X³A″neutral ground states and the singlet-triplet energy gapsΔES-T（kJ/mol）follow this order: FCCN（7.4） < ClCCN（13.4） < BrCCN（16.6）. The calculated most intensive vertical excitation energies of X³A″→2³A″transitions for FCCN, ClCCN, and BrCCN at 408.3, 385.4, and 345.2 kJ/mol, respectively, are mainly attributed to theπ（a′）→nxy transitions. The adiabatic electron affinities for XCCN are found to be 235.7, 233.0, and 237.2 kJ/mol, respectively. Compared with the results of HCCN, the electron affinities are enhanced.更多还原