振动态选择的NO2+离子e3B2态解离生成氧离子通道的动力学

结合最新的阈值光电子-光离子符合速度成像技术和同步辐射光电离, 开展了振动态选择的NO₂⁺离子e³B₂态解离动力学研究. 在18.8-19.2 eV范围内获得的NO₂⁺离子e³B₂态的振动分辨阈值光电子谱与前人结果基本符合, 而由e³B₂态(0,0,0)和(1,0,0)振动能级解离生成的O⁺碎片离子的符合速度成像清楚地显示出多个圆环结构, 表明解离过程中生成了多种具有不同速度的O⁺离子, 对应中性解离碎片NO分子处于不同的内态. 通过速度和角度积分, 我们分别获得了解离过程中释放的总平动能分布和O⁺离子的角度分布, 其中两振动态选择的NO₂⁺离子解离生成的NO分子X²Π态振动分布十分相似, 主要布居的振动量子数为3-5. 解离释放的可资用能近似平均分配到碎片的平动能和内能, 其中碎片总平动能约占52%, 内能约占48%. 此外, O⁺离子的各向异性参数β约为0.3, 且不随NO(X²Π)振动量子数而剧烈变化.     

CH2＝CClF hν >•CH＝CClF＋H光解反应的理论研究

采用UHF, CIS和CASSCF方法, 在aug-cc-pvdz基组水平上对CH₂＝CClF ^hν >•CH＝CClF＋H的光解反应通道及其后续反应作了研究. 计算表明: 分子吸收一个光子后, 在第一电子激发态(S₁)经过一个过渡态解离与Cl原子同侧的C—H键, 这与用CIS方法计算垂直激发得到的π→σ^*_C—H跃迁及其对Frank-Condon点的计算中分子的单占轨道和键电荷密度变化所预测的结果是一致的. 光解产物•CH＝CClF(基态)还可再发生反应, 经过渡态解离C—Cl键或是C—F键.     

溴代烷烃与活性氮的反应发光研究

在流动余辉装置上, 利用N₂空心阴极放电制备活性氮, 研究了活性氮与溴代烷烃(CHBr₃、CH₂Br₂、C₂H₅Br、C₄H₉Br) 反应的化学发光.上述所有反应中, 在550～750 nm波段均观察到了较强的NBr (b¹Σ+→X³Σ^-)跃迁发射谱. 同时在活性氮与CHBr₃和CH₂Br₂的反应中, 在流动管下游还观察到了CN (A²π, B²π→X²Σ⁺)的发射谱. 验证性的实验表明, 激发态NBr (b¹Σ⁺)是由二步过程形成: N(⁴S)与溴代烷烃反应生成NBr (X³Σ^-), 再通过N₂ (A ³Σ_u⁺)分子能量转移到激发态NBr (b¹Σ⁺); 而激发态的CN是通过N(⁴S) + CBr→CN(A, B) + Br过程形成的.     

CH2＝CClF hν >•CH＝CClF＋H光解反应的理论研究

采用UHF, CIS和CASSCF方法, 在aug-cc-pvdz基组水平上对CH₂＝CClF  ^hν >•CH＝CClF＋H的光解反应通道及其后续反应作了研究. 计算表明: 分子吸收一个光子后, 在第一电子激发态(S₁)经过一个过渡态解离与Cl原子同侧的C—H键, 这与用CIS方法计算垂直激发得到的π→σ^*_C—H跃迁及其对Frank-Condon点的计算中分子的单占轨道和键电荷密度变化所预测的结果是一致的. 光解产物•CH＝CClF(基态)还可再发生反应, 经过渡态解离C—Cl键或是C—F键.     

线性BC2nB (n＝1～12)的结构特征和电子光谱的理论研究

应用密度泛函理论, 在B3LYP/6-31G^*水平上优化得到了线性簇合物BC_2nB (n＝1～12, D_(h)的平衡几何构型, 并计算了它们的谐振动频率. 在优化平衡几何构型下, 通过TD-B3LYP/cc-pvDZ和TD-B3LYP/cc-pvTZ计算, 分别得到了n＝1～12和n＝1～7的电子跃迁的垂直激发能和对应的振子强度. 在B3LYP/6-311＋G^*水平上计算得到了簇合物BC_2nB (n＝1～12, D_(h)的电离能. 基于计算结果, 导出了BC_2nB体系电子跃迁能以及第一电离能与体系大小n的解析表达式.     

新型的含硫族元素碳硼烷配体的三(3，5-二甲基-1-吡唑)硼氢钼配合物的合成和分子结构(英)

三齿单核三(3，5-二甲基-1-吡唑)硼氢钼配合物Tp^*Mo(O)Cl₂ (1)(Tp^*=三(3，5-二甲基-1-吡唑)硼氢HB(C₃H(Me₂)N₂)₃)与含硫族元素碳硼烷的锂盐[(THF)₂LiE₂C₂B₁₀H₁₀(THF)]<     

离子速度成像方法研究溴代环己烷的紫外光解动力学

利用二维离子速度成像方法对C6H11Br分子在234 nm附近的光解动力学行为进行了研究. 通过(2+1)共振增强多光子电离探测了光解产物Br*(2P1/2)和Br(2P3/2), 得到它们的相对量子产率. 从光解产物Br*(2P1/2)和Br(2P3/2)的速度图像得到了能量和角度分布. 结果表明, Br*原子主要来自于S1态的直接解离, 而Br则绝大部分是从S2态向T3态的系间交叉跃迁得到, 并导致了两种解离通道能量分布的差别. 实验发现C6H11Br分子解离过程中大部分能量都转化为内能, 但与其它长链溴代烷烃分子相比, 可资用能更多地被分配到平动能中, 结合软反冲模型分析了这种能量分配跟环烷基的构象和稳定性的关系.     

N2O+经由B2Пi←X2П跃迁的光解离机理研究

在超声分子束条件下,利用360.50 nm的电离激光使N₂O分子经由[3+1]共振增强多光子电离（REMPI）产生纯净的N₂O⁺（X²Π（000））分子离子,用另一束解离激光在230-275 nm范围扫描获得N₂O⁺经由B²П_i←X²Π跃迁产生的光解碎片（NO⁺和N₂⁺）激发（PHOFEX）谱. 获得的光解碎片激发谱可以归属为B²П_i（00n）←X²Π（000）序列跃迁. 我们分别将线性三原子分子离子N₂O⁺中N―N伸缩振动简化成NO和N之间的简谐振动,N―O伸缩振动简化成N₂和O之间的简谐振动,用谐振子的简谐势能曲线和波函数对N₂O⁺分子离子X²Π和B²П_i电子态振动能级间跃迁的Franck-Condon因子进行计算,和实验得到的碎片离子增强谱实验强度进行比较,对前人给出的分子数据（分子平衡核间距）进行验证,讨论了N₂O⁺经由B²П_i（00n）←X²Π（000）电子态跃迁的光解离机理和碎片离子的分支比.     

X@(HAlNH)12和X(HAlNH)12 (X＝F－, Cl－, Br－, O2－, S2－, Se2－)复合物的结构和稳定性

用DFT的B3LYP方法在6-31G(d)基组的水平上, 对闭式多面体簇合物(HAlNH)₁₂及其内含式X@(HAlNH)₁₂和外接式X(HAlNH)₁₂ (X＝F^－, Cl^－, Br^－, O^2－, S^2－, Se^2－)复合物的结构进行了构型优化和能量计算, 并讨论了几何构型、自然键轨道(NBO)、振动频率、能量参数及NMR数据与结构的关系, 最后得到复合物结构的稳定性信息, 具有T_h对称性的X@(HAlNH)₁₂ (X＝F^－, Cl^－, Br^－, S^2－, Se^2－)复合物和具有C₃对称性的O^2－@(HAlNH)₁₂复合物为内含式的基态结构, 从能量角度分析, 内含式复合物比外接式复合物的结构稳定.     

巢式十一顶铂硼烷簇合物的合成与晶体结构

[PtCl₂(PPh₃)₂]与B₁₀H₁₀^2－在异丙醇中回流反应, 得到3个巢式十一顶铂十硼烷簇合物: [(PPh₃)₂PtB₁₀H₁₁-9-O-i-Pr] (1), [(PPh₃)₂PtB₁₀H₁₀-8,10-(O-i-Pr)₂] (2)和[(PPh₃)₂PtB₁₀H₁₁-8-O-i-Pr] (3). 簇合物1～3都具有PtB₁₀多面体骨架结构, 其中Pt原子位于敞开的PtB₄面上, 且与4个B原子成键, 每个Pt原子还与2个PPh₃基团中的P原子成键. 将溶剂热合成的方法引入到硼簇合物的合成中并进行同一反应, 得到2个B₁₀H₁₀^2－降解的巢式十一顶双铂九硼烷簇合物: [(PPh₃)₂(μ-PPh₂)Pt₂B₉H₆-3,9,11-(O-i-Pr)₃] (4)和[(PPh₃)₂(μ-PPh₂)Pt₂B₉H₆-3,9-(O-i-Pr)₂-11-Cl] (5). 簇合物4和5都具有Pt₂B₉多面体骨架结构, 2个Pt原子位于敞开的Pt₂B₃面上的相邻位置, 且由一个PPh₂基团桥连, 每个Pt原子还与3个B原子和一个PPh₃基团中的P原子成键. 通过红外光谱、元素分析、X射线单晶衍射对5个簇合物进行了结构表征.     

Photodissociation dynamics of CH(2)Br(2) near 234 and 267 nm

The photodissociation dynamics of CH(2)Br(2) was investigated near 234 and 267 nm. A two-dimensional photofragment ion velocity imaging technique coupled with a [2+1] resonance-enhanced multiphoton (REMPI) ionization scheme was utilized to obtain the angular and translational energy distributions of the nascent Br ((2)P(3/2)) and Br* ((2)P(1/2)) atoms. The obtained translational energy distributions of Br and Br* are found consist of two components which should be come from the radical channel and secondary dissociation process, respectively. It is suggested that the symmetry reduction from C(2v) to C(s) during photodissociation invokes a non-adiabatic coupling between the 2B(1) and A(1) states. Consequently, the higher internal energy distribution of Br channel than Br* formation channel and the broader translational energy distribution of the former are presumed correlate with a variety of vibrational excitation disposal at the crossing point resulting from the larger non-adiabatic crossing from 2B(1) to A(1) state than the reverse crossing. Moreover, the measured anisotropy parameter beta indicate that fragments recoil along the Br-Br direction mostly in the photodissociation.     

离子速度影像法研究n-C7H15Br分子光解反应动力学

利用离子速度成像方法, 研究n-C7H15Br分子在231～239 nm范围内几个波长处的光解离动力学. 通过同一束激光经(2+1)共振多光子电离(REMPI)过程探测光解碎片Br(2P3/2)和Br*(2P1/2), 得到了不同激光波长处的离子速度分布图像, 从而获得C7H15Br光解产物的能量分配和角度分布. 结合各向异性参数和量子产率, 计算了n-C7H15Br分子在234 nm波长下不同解离通道的比例. 实验表明光解产物的能量分配可以用冲击模型中的软碰撞模型来解释. 实验还发现, 各向异性参数β(Br*)的值对光波长变化很敏感, 这是由电子激发态的绝热和非绝热过程决定的.     

Photodissociation dynamics of allyl bromide at 234, 265, and 267 nm

The photodissociation dynamics of allyl bromide was investigated at 234, 265, and 267 nm. A two-dimensional photofragment ion velocity imaging technique coupled with a [2+1] resonance-enhanced multiphoton ionization scheme was utilized to obtain the angular and translational energy distributions of the nascent Br* (2P1/2) and Br (2P3/2) atoms. The Br fragments show a bimodal translational energy distribution, while the Br* fragments reveal one translational energy distribution. The vertical excited energies and the mixed electronic character of excited states were calculated at ab initio configuration interaction method. It is presumed that the high kinetic energy bromine atoms are attributed to the predissociation from 1(pipi*) or 1(pisigma*) state to the repulsive 1(nsigma*) state, and to the direct dissociation from 3(nsigma*) and 3(pisigma*) states, while the low kinetic energy bromine atoms stem from internal conversion from the lowest 3(pipi*) state to 3(pisigma*) state.     

2-溴噻吩和3-溴噻吩在267 nm的C-Br键解离机理

利用离子速度影像技术, 研究了2-溴噻吩和3-溴噻吩两种同分异构体在267 nm激光作用下的C—Br键解离机理, 获得了光解产物Br(2P3/2)和Br*(2P1/2)的能量和角度分布, 分析了两异构分子在267 nm 的C—Br键解离通道. 对于2-溴噻吩和3-溴噻吩, 产物Br来源于三个通道: (i) 从单重激发态系间窜跃到排斥的三重激发态的快速预解离; (ii)单重激发态内转化到高振动基态的热解离; (iii) 母体分子多光子电离后的解离. 2-溴噻吩的产物Br*具有类似的产生机制; 但对于3-溴噻吩, 从激发态内转换到高振动基态发生热解离成为产物Br*的主导通道, 而来自激发三重态的快速预解离通道则几乎消失. 定量地给出了各个通道的相对贡献、能量分配及各向异性分布信息. 实验发现, 随着溴原子在噻吩上取代位置远离硫原子, 来自通道(i)和(ii)产物之间的比例明显减小, 相应的各向异性分布有变弱趋势.     

Multiphoton dissociative ionization of tert-pentyl bromide near 265 nm

We report on the photodissociation dynamics of tert-pentyl bromide near 265 nm investigated by time-sliced velocity map imaging. The speed and angular distributions have been analyzed for both the ground-state Br((2)P(3∕2)) atom (denoted Br) and the spin-orbit excited-state Br((2)P(1∕2)) atom (denoted Br*). The speed distributions of Br and Br* atoms are all found to consist of three Gaussian components, which correlate to three independent dissociation pathways on the excited potential energy surfaces: (1) the high translational energy (E(T)) component from the prompt dissociation along the C-Br stretching mode, (2) the middle E(T) component from the repulsive mode along the C-Br stretching coupled with some bending motions, and (3) the low E(T) component from the repulsive mode along the C-Br stretching coupled with more bending motions. More interestingly, we have also observed the tert-C(5)H(11)(+) ions in 263-267 nm. The near-zero kinetic energy distributions extracted from the three tert-C(5)H(11)(+) images near 265 nm show the typical characteristics that are attributable to multiphoton dissociative ionization, suggesting the existence of a neutral superexcited state of the parent tert-pentyl bromide molecule. The contribution of bromine atoms formed in this dissociative ionization channel adds in the total relative distribution of low E(T) component in the Br*(Br) formation channel, which reasonably explains the abnormal distributions observed in between the middle and low E(T) components in the Br*(Br) formation channel.     

Br(2Pj) atom formation dynamics in ultraviolet photodissociation of tert-butyl bromide and iso-butyl bromide

The photodissociation dynamics of tert-C(4)H(9)Br and iso-C(4)H(9)Br has been studied at 234 and 265 nm using two-dimensional velocity map imaging technique. The translational energy and angular distributions have been analyzed for Br, Br(*), and tert-C(4)H(9) radical. The energy distribution of Br atom in the photodissociation of tert-C(4)H(9)Br is found to consist of two Gaussian components. The two components are correlated to two independent reaction paths on the excited potential energy surfaces: (1) the high-energy component from the prompt dissociation along the C-Br stretching mode and (2) the low-energy component from the repulsive mode along the C-Br stretching, coupled with some bending motions. For the energy distribution of Br(*) atom in the photodissociation of tert-C(4)H(9)Br, a third multiphoton dissociative ionization channel is observed at 265 nm in addition to the two energy components corresponding to channels (1) and (2). The energy distributions of Br and Br(*) atoms in the photodissociation of iso-C(4)H(9)Br can be fitted using only one Gaussian function indicating a single formation channel. Relative quantum yields for Br((2)P(32)) at 234 and 265 nm in the photodissociation of tert-C(4)H(9)Br are measured to be 0.76 and 0.65, respectively. For iso-C(4)H(9)Br, the measured value is Phi(234 nm)(Br)=0.81. The contribution of bending modes to Br and Br(*) is much more obvious in the photodissociation of tert-C(4)H(9)Br than in iso-C(4)H(9)Br.     

A photodissociation study of CH2BrCl in the A-band using the time-sliced ion velocity imaging method

Employing a high-resolution (velocity resolution deltanu/nu<1.5%) time-sliced ion velocity imaging apparatus, we have examined the photodissociation of CH2BrCl in the photon energy range of 448.6-618.5 kJ/mol (193.3-266.6 nm). Precise translational and angular distributions for the dominant Br(2P32) and Br(2P12) channels have been determined from the ion images observed for Br(2P32) and Br(2P12). In confirmation with the previous studies, the kinetic-energy distributions for the Br(2P12) channel are found to fit well with one Gaussian function, whereas the kinetic- energy distributions for the Br(2P32) channel exhibit bimodal structures and can be decomposed into a slow and a fast Gaussian component. The observed kinetic-energy distributions are consistent with the conclusion that the formation of the Br(2P32) and Br(2P12) channels takes place on a repulsive potential-energy surface, resulting in a significant fraction (0.40-0.47) of available energy to appear as translational energy for the photo fragments. On the basis of the detailed kinetic-energy distributions and anisotropy parameters obtained in the present study, together with the specific features and relative absorption cross sections of the excited 2A', 1A", 3A', 4A', and 2A" states estimated in previous studies, we have rationalized the dissociation pathways of CH2BrCl in the A-band, leading to the formation of the Br(2P32) and Br(2P12) channels. The analysis of the ion images observed at 235 nm for Cl(2P(32,12)) provides strong evidence that the formation of Cl mainly arises from the secondary photodissociation process CH2Cl + hnu --> CH2 + Cl.     

Ion-pair formation dynamics of F(2) at 18.385 eV studied by velocity map imaging method

We studied the ion-pair formation dynamics of F2 at 18.385 eV (67.439 nm) using the velocity map imaging method. It was found that there are two dissociation channels corresponding to production of F(+)((1)D(2)) + F(-)((1)S(0)) and F(+)((3)P(j)) + F(-)((1)S(0)). The measured center-of-mass translational energy distribution shows that about 98% of the dissociation occurs via the F(+)((1)D(2)) channel. The measured angular distributions of the photofragments indicate that dissociation for the F(+)((3)P(j)) channel occurs via predissociation of Rydberg states converging to F(2)(+)(A(2)Pi(u)) and dissociation for the F(+)((1)D(2)) channel involves mainly a direct perpendicular transition into the ion-pair state, or X(1)Sigma(g)(+) --> 2(1)Pi(u), which is also supported by the transition dipole moment calculations .     

Photodissociation dynamics of CBr4 at 267 nm by means of ion velocity imaging

The photodissociation dynamics of CBr4 at 267 nm has been studied using time of flight (TOF) mass spectrometry and ion velocity imaging techniques. The photochemical products are detected with resonance enhanced multiphoton ionization (REMPI) as well as single-photon vacuum ultraviolet ionization at 118 nm. REMPI at 266.65 and 266.71 nm was used to detect the ground Br(2P32) and spin-orbit excited Br(2P12) atoms, respectively. The translational energy and angular distributions are consistent with direct dissociation from an excited triplet state and indirect dissociation from high vibrational levels on the singlet ground state surface. Br2+ ions are also observed in the TOF spectra with a focused 267 nm laser. The counter fragment, CBr2+, is observed when this photolysis laser is unfocused, and photons at 118 nm are used to ionize the radical products. The translational energy distributions of the CBr2+ and Br2+ products can be momentum matched, which indicates that molecular Br2 elimination is one of the primary dissociation channels.