离子速度成像方法研究碘代正戊烷的紫外光解动力学

利用离子速度成像方法对n-C5H11I分子在266和277 nm下的光解动力学进行了研究. 实验分析了I*(5p 2P1/2)和I(5p 2P3/2)的离子影像, 得到其相应速度、角度分布和相对量子产率, 并根据相对量子产率和角度分布计算了不同解离通道的比例. 实验发现n-C5H11I的3Q0和1Q1态之间存在较强的耦合效应, 并且随着波长的减小, 这种非绝热耦合作用有递增的趋势. 由离子影像(I*和I)的角度分布结果发现, 在同一解离激光波长下I*的各向异性参数β值比I的β值小, 其中I*主要由3Q0直接解离产生, 而I绝大多数是由分子先跃迁到3Q0再经过3Q0→1Q1的非绝热耦合产生.     

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.     

CF_3I在238 nm的光解碎片平动能谱研究:CF_3光解碎片的振动态分布和势能曲线交叉穿越几率

利用高分辨弱电场加速型光解碎片平动能谱仪,对CF3I在238 nm的光解动力学进行了研究.结果表明,来自3Q0平行跃迁的I*通道[CF3I(X)hν→‖CF3I(3Q0)→CF3(ν1,ν2)+I*],信号最强,并可以分辨出碎片CF3(ν1,ν2)的振动峰.通过对峰间距的分析,可以基本分辨出同时具有CF3碎片的振动波带CF3(ν1,ν2=0)与CF3(ν1,ν2=1).其中ν1=701 cm-1为对称伸缩振动,ν2=1086 cm-1为CF3伞形振动.测量了这些振动态的分布及振动波带分配比为∑P(ν1,1)/∑P(ν1,0)=0.48/0.52.还测得238 nm处4个光解通道的分支比:通道1(X→3Q0→I*)为0.664,通道2(X→3Q0→1Q1→I)为0.084,通道3(X→1Q1→I)为0.178,通道4(X→1Q1→3Q0→I*)为0.074.实验结果表明,3Q0→1Q1过程中的势能曲线交叉穿越几率P0→1=0.112,1Q1→3Q0过程中P1→0=0.294;I*通道的各向异性参数β(I*)=1.70,I通道β(I)=-0.04.     

n-C_3H_7I和i-C_3H_7I的激光裂解

Wilson等人曾研究过碘代烷在266nm的激光光解RI→R+I＊(~2P_(1/2))(1)RI→R+I(~2P_(3/2))(2)由于他们所用的光解产物谱仪不能改变产物的检测方向,因而对C_2H_5I,n-C_3H_7I和i-C_3H_7I的光解通道(1)和(2)在飞行时间(TOF)谱上的分离没有成功。我们用束源可转动的分子束激光裂解产物谱仪(飞行距离531mm)研究了CH_3I和C_2H_5I在248nm的激光裂解后,又分别对n-C_3H_7I和i-C_3H_7I进行研究,并实现了I＊(~2P_(1/2))和I(~2P_(3/2))光解通道在TOF谱上的分离,测得光解通道比见表1。     

F原子与i-C3H7I反应的动力学研究

本文利用交叉分子束技术和激光诱导萤光方法, 研究了F+i-C3H7I→IF+i-C3H7反应的动力学过程. 获得了产物IF相对初生振动分布和相对细致反应速率常数. 初生态布居接近于模型III下的统计理论斯待值, 这不仅表明反应经过长寿命“配合物", 而且也说明自由基i-C3H7的内态是激发的. 另外, 确定了反应的产物IF内部能量分配和总反应截面σ, σ=(3.6±0.5)×10^-^1^6cm^2.     

氯碘甲烷在A带的光解动力学

利用离子速度影像方法结合共振增强多光子电离(REMPI)技术研究了氯碘甲烷在A带的光解机理. 从266和277 nm的I*(5p 2P1/2)和I(5p 2P3/2)离子速度影像获得了碎片的平动能分布和角度分布. I和I*的平动能分布呈单高斯型, 可用软自由基近似来解释. I和I*是在排斥的势能面上直接解离产生的. 实验得到的各向异性参数β证实分子受激发后主要产生3Q0态, 并且3Q0和1Q1态之间存在非绝热转移. 波长越短, 这种非绝热转移越强. 在235 nm附近, Cl和Cl*各向同性的离子影像说明氯原子来自于CH2ICl的二次解离过程, 即CH2ICl先解离产生CH2Cl自由基, 自由基再解离产生氯原子.     

辅酶B_(12)模型化合物的研究(V)RCo(Salen)L配合物Co—C键断裂的动力学

运用光度法研究了RCo(Salen)L配合物在甲醇中热分解反应动力学;测定了Co—C键断裂的速率常数及活化能,得到表观速率常数顺序为i-C3H7>i-C4H9>n-C4H9>n-C3H7>C2H5,活化能顺序为i-C3H7相似文献   

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.     

CH_3I分子束激光裂解产物的分布

CH_3I的裂解与某些特殊的直线形三原子分子相似,有重要研究意义。Y.T.Lee等曾用266nm激光研究CH_3I分子束的光解,测量了CH_3碎片的高分辨飞行时间谱。我们利用自己设计制造的束源转动型分子束激光光解装置,用KrF激光(249nm)裂解CH_3I,载气为空气。用自制的四极质谱仪和离子计数检测系统,以及PAR的多通道讯号分析器,测量了Ⅰ碎片(M=127)的高分辨飞行时间谱,也得到Ⅰ~*和Ⅰ的两个峰。当分子束与     

OH+C_2H_2N←C_2H_3+NO→OH+C_2H_2N反应机理的密度泛函理论研究

应用密度泛函理论研究了反应通道(a)C2H3+NO→CH3+NCO和(b)C2H3+NO→OH+C2H2N的反应机理.在B3LYP/6-31G(d)水平上优化了反应物、中间体、过滤态、产物的几何构型,通过频率分析确定了11个中间体和10个过渡态.所有的反应物、中间体、过渡态、产物都在CCSD/6-311++G(d,p)水平上进行了单点能较正.并讨论了反应的异构化过程.计算结果表明10是能量最低的中间体,比反应物的能量低308 479kJ/mol;过渡态1/3,2/5,3/4,4/8比反应物的能量高,其中3/4是能量最高的过渡态,比反应物的能量高91 894kJ/mol.通道(a)和(b)的理论放热值分别为111 059和96 619kJ/mol.     

Photofragment translational spectroscopy of n-C3H7I and i-C3H7I near 280 and 304 nm

The photodissociation dynamics of propyl iodides n-C3H7I and i-C3H7I near 280 and 304 nm has been investigated with our mini-TOF photofragment translational spectrometer. When a single laser is applied for both the photodissociation of parent molecules and the REMPI of I atom photofragments, the TOF spectra of photofragments I*(2P1/2) and I (2P3/2) are obtained at four different wavelengths for these two iodides. For n-C3H7I, some small vibrational peaks are partially resolved (with separation of approximately 522 cm-1, corresponding to the RCH2 deformation frequency of the fragment n-C3H7) at 281.73, 279.71, and 304.67 nm. These results show that the RCH2 deformation is mostly excited. For i-C3H7I, we obtain some partially resolved vibrational peaks (with separation of approximately 352 cm-1, corresponding to the HC(CH3)2 out-of-plane bending frequency of the fragment i-C3H7) at 281.73 nm only. For n-C3H7I, the partitioning values of the available energy Eint/Eavl are 0.48 at 281.73 nm and 0.49 at 304.02 nm for the I* channel, and 0.52 at both 279.71 and 304.67 nm for the I channel. These energy partitioning values are comparable with the previous results at different wavelengths in the literature. For i-C3H7I, the Eint/Eavl values are 0.61 at 281.73 nm, 0.65 at 304.02 nm for the I* channel, and 0.62 at 279.71 nm, 0.49 at 304.67 nm for the I channel. The potential-energy-surface crossing and the beta values have also been discussed.     

Photoionization of hot radicals: C2H5, n-C3H7, and i-C3H7

The combination of ion-imaging and vacuum-ultraviolet (vuv) single-photon ionization is used to study the internal energy dependence of the relative photoionization yields of the C(2)H(5),n-C(3)H(7), and i-C(3)H(7) radicals following the 266 nm photodissociation of the corresponding alkyl iodides. The comparison of the ion images obtained by vuv photoionization of the radical with those obtained by two-photon-resonant, three-photon ionization of the complementary I (2)P(32) and I*(2)P(12) atoms allows the extraction of the internal energy dependence of the cross sections. Factors influencing the appearance of the ion images in the different detection channels are discussed, including the secondary fragmentation of the neutral radicals, Franck-Condon factors for the photoionization process, and the unimolecular fragmentation of the parent photoions.     

Nonadiabatic photodissociation dynamics in (HI)2 induced by intracluster collisions

The sequential photodissociation dynamics of (HI)2 is studied by means of a nonadiabatic wave packet treatment starting from the I*-HI complex. The model reproduces the main experimental findings for photolysis with 266 nm radiation. The results confirm that some of the H atoms dissociated from the I*-HI complex deactivate the I* atom through a HI* intracluster collision which induces an I*-->I electronically nonadiabatic transition. As a consequence, these H fragments become very fast by acquiring nearly all the I* excitation energy, equivalent to the I*I spin-orbit splitting. A most interesting result is the high production of bound I2 fragments in highly excited rovibrational states in the photolysis, indicating that the H dissociation is mainly direct.     

Measurements and modeling of HO2 formation in the reactions of n-C3H7 and i-C3H7 radicals with O2

The formation of HO(2) in the reactions of C(2)H(5), n-C(3)H(7), and i-C(3)H(7) radicals with O(2) is investigated using the technique of laser photolysis/long-path frequency-modulation spectroscopy. The alkyl radicals are formed by 266 nm photolysis of alkyl iodides. The formation of HO(2) from the subsequent reaction of the alkyl radicals with O(2) is followed by infrared frequency-modulation spectroscopy. The concentration of I atoms is simultaneously monitored by direct absorption of a second laser probe on the spin-orbit transition. The measured profiles are compared to a kinetic model taken from time-resolved master-equation results based on previously published ab initio characterizations of the relevant stationary points on the potential-energy surface. The ab initio energies are adjusted to produce agreement with the present experimental data and with available literature studies. The isomer specificity of the present results enables refinement of the model for i-C(3)H(7) + O(2) and improved agreement with experimental measurements of HO(2) production in propane oxidation.     

Productions of I, I*, and C2H5 in the A-band photodissociation of ethyl iodide in the wavelength range from 245 to 283 nm by using ion-imaging detection

Photodissociation dynamics of ethyl iodide in the A band has been investigated at several wavelengths between 245 and 283 nm using resonance-enhanced multiphoton ionization technique combined with velocity map ion-imaging detection. The ion images of I, I(*), and C(2)H(5) fragments are analyzed to yield corresponding speed and angular distributions. Two photodissociation channels are found: I(5p (2)P(3/2))+C(2)H(5) (hotter internal states) and I(*)(5p (2)P(1/2))+C(2)H(5) (colder). In addition, a competitive ionization dissociation channel, C(2)H(5)I(+)+h nu-->C(2)H(5)+I(+), appears at the wavelengths <266 nm. The I/I(*) branching of the dissociation channels may be obtained directly from the C(2)H(5) (+) images, yielding the quantum yield of I(*) about 0.63-0.76, comparable to the case of CH(3)I. Anisotropy parameters (beta) determined for the I(*) channel remain at 1.9+/-0.1 over the wavelength range studied, indicating that the I(*) production should originate from the (3)Q(0) state. In contrast, the beta(I) values become smaller above 266 nm, comprising two components, direct excitation of (3)Q(1) and nonadiabatic transition between the (3)Q(0) and (1)Q(1) states. The curve crossing probabilities are determined to be 0.24-0.36, increasing with the wavelength. A heavier branched ethyl group does not significantly enhance the I(5p (2)P(3/2)) production from the nonadiabatic contribution, as compared to the case of CH(3)I.     

Modeling the (HI)2 photodissociation dynamics through a nonadiabatic wave packet study of the I*-HI complex

The nonadiabatic photodissociation dynamics of (HI)2 is simulated by applying a wave packet approach which starts from the I*-HI complex (where I* denotes the I(2P1/2) excited electronic state) produced after the photodissociation of the first HI moiety within (HI)2. In the model, two excited electronic potential surfaces corresponding to I*-HI(A 1Pi1) and I-HI(A 1Pi1), which interact through spin-rotation coupling, are considered. The simulations show that upon photodissociation of HI within I*-HI, the dissociating H fragment undergoes intracluster collisions with the I* atom. Some of these collisional events induce an electronically nonadiabatic transition which causes the deactivation of I* to the I ground electronic state. The probability of such nonadiabatic process is found to be 0.37%. Most of the photodissociation process takes place in the upper excited electronic surface [that of the I*-HI(A 1Pi1) complex], where H dissociation is found to be mainly direct or involving weak H/I* intracluster collisions. These weak collisions with high collisional angular momentum, and therefore high collisional impact parameters associated, are responsible for most of the probability of nonadiabatic transitions found. The type of H/I* collisions leading to nonadiabatic transitions appears to be closely related to the nature of the spin-rotation coupling between the two excited electronic states involved.     

Kinetics of the reactions of Cl*(2P(1/2)) and Cl(2P(3/2)) atoms with CH3OH, C2H5OH, n-C3H7OH, and i-C3H7OH at 295 K

The title reactions were studied using laser flash photolysis/laser-induced-fluorescence (FP-LIF) techniques. The two spin-orbit states, Cl*(2P(1/2)) and Cl(2P(3/2)), were detected using LIF at 135.2 and 134.7 nm, respectively. Measured reaction rate constants were as follows (units of cm3 molecule(-1) s(-1)): k(Cl(2P(3/2))+CH3OH) = (5.35 +/- 0.24) x 10(-11), k(Cl(2P(3/2))+C2H5OH) = (9.50 +/- 0.85) x 10(-11), k(Cl(2P(3/2))+n-C3H7OH) = (1.71 +/- 0.11) x 10(-10), and k(Cl(2P(3/2))+i-C3H7OH) = (9.11 +/- 0.60) x 10(-11). Measured rate constants for total removal of Cl*(2P(1/2)) in collisions with CH3OH, C2H5OH, n-C3H7OH, and i-C3H7OH were (1.95 +/- 0.13) x 10(-10), (2.48 +/- 0.18) x 10(-10), (3.13 +/- 0.18) x 10(-10), and (2.84 +/- 0.16) x 10(-10), respectively; quoted errors are two-standard deviations. Although spin-orbit excited Cl*(2P(1/2)) atoms have 2.52 kcal/mol more energy than Cl(2P(3/2)), the rates of chemical reaction of Cl*(2P(1/2)) with CH3OH, C2H5OH, n-C3H7OH, and i-C3H7OH are only 60-90% of the corresponding Cl(2P(3/2)) atom reactions. Under ambient conditions spin-orbit excited Cl* atoms are responsible for 0.5%, 0.5%, 0.4%, and 0.7% of the observed reactivity of thermalized Cl atoms toward CH3OH, C2H5OH, n-C3H7OH, and i-C3H7OH, respectively.