【作者】 舒鑫；

【导师】 张红星；

【作者基本信息】 吉林大学 ， 物理化学， 2009， 博士

【摘要】 激发态是原子、分子和离子存在的重要形态。分子激发态的结构、特性和行为,如能级、寿命、预解离和自电离等,与许多化学反应的动力学性质直接相关。分子激发态,特别是高能电子激发态的研究,是分子物理学和理论化学的重要前沿。含有硫元素的小分子以及具有高偶极矩的累接双键烃分子的气相光谱,在大气化学、星际化学和燃烧化学中的研究一直以来受到光谱学工作者的广泛关注。本文采用了全活化空间自洽场(CASSCF)方法,对H2CCC, H2CCSi, HSiCN, HSiNC分子及其阴阳离子,CH3SS分子及其阳离子的激发态性质进行了深入的研究。主要的内容概括如下:1.使用CASPT2//CASSCF理论方法,在Cs对称性和ANO-S基组水平下,研究了H2CCC及它的同族类似物H2CCSi自由基及其阴阳离子的基态和低能激发态的性质。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H2CCC和H2CCSi自由基基态的几何构型基础上,分别计算了H2CCC和H2CCSi的垂直激发能。对于H2CCC,X1A1→1A2,X1A1→1B1和X1A1→21A1在159.0 kJ/mol,216.5 kJ/mol和476.4 kJ/mol处的激发可分别归因于π(b2)→π*(b1),n(a1)→π*(b1)和π(b1)→π*(b1)的跃迁特征,理论波长与紫外吸收光谱得到的实验数据一致;对于H2CCSi,最强的跃迁发生在348.2 kJ/mol处的X1A1→1B1的电子跃迁,归因于n(a1)→π*(b1)的跃迁特征,并且激发能最低。在CASPT2//CASSCF理论水平下,计算得到了H2CCC和H2CCSi的垂直和绝热电离能。所得到的数据为实验上进一步研究H2CCC和H2CCSi提供了理论依据。2.使用CASPT2//CASSCF理论方法,在Cs对称性和aug-cc-pVTZ基组水平下,使用全价电子活化空间即包含13个活化轨道和14,15和13个活化电子,分别计算了HSiCN和HSiNC及其阴阳离子的基态和激发态的几何结构、能量以及电子排布和振动频率,并对吸收光谱进行了研究,计算了HSiCN和HSiNC自由基5个电子态的几何结构,在CASPT2水平上做了单点能校正,计算得到的几何结构与以前的理论和实验值是一致的。同时计算得到的谐振频率值与实验值符合得较好。第一电子激发态为3A″,其与基态之间的能隙差(单-三重态的劈裂能)分别为0.99和1.40 eV,-CN和-NC的取代加大了SiH2的单-三重态的能隙差,并且HSiCN的单-三重态的能隙差大于HSiNC。基于在CASSCF水平上得到的电子结构,合理地解释了各个电子激发态对于电子基态的几何结构的变化。通过垂直激发计算得到了比较完整的吸收光谱。3.使用CASPT2//CASSCF理论方法,在Cs对称性和ANO-S基组水平下,研究了CH3SS自由基及其阳离子的基态和低能激发态的性质。对CH3SS自由基优化了五个电子态的结构,其中基态为X2A" ,电子结构为(core)(12a’)2(3a")2(13a’)2(14a’)2(15a’)2(4a")2(16a’)2(5a")α,计算得到的几何参数与其他人得到的理论值符合得很好。计算得到了CH3SS的垂直和绝热激发能,在跃迁允许的激发当中,在3.349 eV处,X2A″→22A″具有最大的跃迁强度f = 0.04,归因于4a"→5a"的单电子跃迁,具有π(a")→π*(a")的跃迁特征。通过分别优化CH3SS基态和对应的阳离子各个电子态得到的能量差,得到了绝热电离能。在优化得到的CH3SS的基态几何结构的基础上,计算了垂直电离能,合理地解释了CH3SS的光电子能谱(PES),计算得到CH3SS自由基的第一垂直电离能为8.525 eV与实验值8.630±0.02 eV符合得很好。更多还原

【Abstract】 The small molecules and radicals including Si atom and the hydrocarbon molecule with high dipole like cumulene carbenes which are detected in the interstellar medium have received much attention. These molecules and radicals not only participate in many photochemistry and photophysical reactions but have been involved in combustion chemistry and interstellar chemistry as well. There have been considerable interests in the sulphur compounds, both experimentally and theoretically, due to important role of these species in the air pollution. As a result, quantum chemical investigations on the excited states of these molecules and free redicals is becoming necessary and meaningful, so in this thesis high level ab initio method CASPT2//CASSCF have been used to perform investigation on H2CCC, H2CCSi, HSiCN, HSiNC and CH3SS molecule radicals. The main results are summarized as follows:1.CASPT2(multiconfiguration second-order perturbation theory)// CASSCF(Complete active space self-consistent field) calculations with ANO-S basis set in C2v symmetry were performed for several electronic states of H2CCC and H2CCSi. The geometries, vibrational frequencies and energies of the ground states and low-lying excited states are obtained from the theoretical investigations. The electronic configurations are used to explain the geometrical alteration in detail. The ground states of H2CCC and H2CCSi turned out to be X1A1. The CASSCF geometry for the ground state of H2CCC and H2CCSi are compared with the experimental geometry. And the calculated harmonic freqencies of the H2CCC and H2CCSi are in agreement with the experimental data. The singlet-triplet energy gap of H2CCC(106.1 kJ/mol) is larger than that of H2CCSi(98.4 kJ/mol).We have presented results from a fully correlated ab initio investigation of the electronic spectrum of H2CCC and H2CCSi neutral radical by means of using CASPT2//CASSCF method, a well-established procedure for accurated calculations of electronic spectra of molecules. The results (CASPT2 vertical excitation energies and RASSI oscillator strengths) suggest that the calculated most intensive transition of H2CCC and H2CCSi at 476.4 kJ/mol and 348.2 kJ/mol are attributed to the X1A1→21A1 and X1A1→1B1, respectively. The most intensive absorption peak is red shifted.CASPT2//CASSCF calculations with ANO-S basis set in C2v symmetry were also performed for a large number of electronic states of the H2CCC+ and H2CCSi+. Based on the corresponding results, the PES of the H2CCC and H2CCSi are assigned. The vertical and adiabatic ionization energies assigned to 15 and 16 ionic states for H2CCC and H2CCSi at the CASPT2 level, respectively. The computed first VIP/AIP of H2CCC(993.9/979.3 kJ/mol) are larger than that of H2CCSi( 779.5/773.8 kJ/mol).Due to H2CCC neutral radical’s high dipole moment, all excited H2CCC- negative ion states can be characterized as dipole-bound states, but its homolog H2CCSi has valence anion excited state. The first adiabatic electronic affinity of H2CCC(160.1 kJ/mol) is larger than that of H2CCSi(100.1 kJ/mol). 2. Equilibrium geometries of low-lying electronic states of cyanosilylene (HSiCN), isocyanosilylene (HSiNC), and their ions have been investigated using the complete active space self-consistent field (CASSCF) approach. The harmonic vibrational frequencies on the optimized geometries were calculated using the multiconfiguration linear response (MCLR) method. Taking the further correlation effects into account, the complete active space perturbation theory of second-order (CASPT2) was carried out for the energetic correction. The CASPT2 calculations have been performed to obtain the vertical excitation energies of selected low-lying excited states of HSiCN and HSiNC. Computed results show that the singlet-triplet splitting energies are calculated to be 0.99 eV and 1.30 eV for HSiCN and HSiNC, respectively. The vertical excitation energies of the lowest singlet and triplet excited states in HSiCN are lower than those in HSiNC. The first vertical ionization energy of HSiCN (10.04 eV) is higher than that of HSiNC (9.97 eV). The ground-state adiabatic electron affinities are found to be rather high, and the value of HSiCN (1.87 eV) higher than that of HSiNC (1.86 eV). The existences of dipole-bound excited negative ion states have been discovered within HSiCN and HSiNC.3. CASPT2//CASSCF calculations with ANO-S basis sets were performed for 5 and 8 low-lying electronic states of CH3SS and CH3SS+ in Cs symmetry, respectively. All calculated states are valence states and their character are discussed in detail. The ground state of CH3SS is X2A", which has a leading electronic configuration (core)(12a’)2(3a")2(13a’)2 (14a’)2(15a’)2(4a")2(16a’)2 (5a")α. The calculated the harmonic frequency of the ground stateν7(a’) = 582 cm-1(S-S stretch)are in great agreement with the experimental data(610±160 cm-1).The electronic configurations are used to explain the geometrical alteration in detail.The ionization energies are obtained to compare with the PES data. The results are in agreement with previous experimental data.更多还原