氟里昂113在多频强红外场离解过程中的V-V能量转移

用TEACO₂激光9P(24),9P(22),9P(20),9P(18)四支线组成的多频强红外场“超激发”氟里昂₁₁₃分子,使其达到很高激发态。由分解曲线可以看出CF₂Cl·CFCl₂与CF₃·CCl₃之间的V-V能量转移有明显的“虹吸”作用。从所得主要产物C₂P₆,C₂Cl₆,C_关键词：     

氟里昂_(113)在多频强红外场离解过程中的V-V能量转移

用TEACO_2激光9P(24),9P(22),9P(20),9P(18)四支线组成的多频强红外场“超激发”氟里昂_(113)分子,使其达到很高激发态。由分解曲线可以看出CF_2Cl·CFCl_2与CF_3·CCl_3之间的V-V能量转移有明显的“虹吸”作用。从所得主要产物C_2P_6,C_2Cl_6,C_2F_4和C_2F_2Cl_2表明,离解过程中主要打断了CF_2Cl·CFCl_2及CF_3·CCl_3分子中具有较高键能的C—C键,而最低键能的C-Cl键开裂很少。我们还提出了在多频强红外场中氟里昂_(113)的离解机理,指出分子内的V-V能量转移是非随机化的。     

富勒烯衍生物C60（CF3）n（n=2，4，6，10）几何结构和电子性质变化规律的密度泛函研究

采用密度泛函理论中的广义梯度近似对C₆₀（CF₃）_n （n=2,4,6,10）几何结构和电子性质的变化规律进行了计算研究.发现在C₆₀（CF₃）₄可能稳定存在的三种同分异构体中,具有p p p加成方式的衍生物热力学性质最为稳定;在C₆₀（CF₃）₆可能稳定存在的三种同分异构体中,具有p p p m p加成方式的衍生物热力学性质最为稳定.对C₆₀（CF₃）₂,C₆₀（CF₃）₄,C₆₀（CF₃）₆和C₆₀（CF₃）₁₀四种加成衍生物的几何结构分析可知：随着CF₃加成个数的增加,C₆₀中的C—C平均键长逐渐变大,笼子与CF₃之间连接键C_C60—C_CF3逐渐变大.对它们的电子结构分析可知,随着CF₃加成数目的增多,反应热几乎是线性增加.而C₆₀（CF₃）_n（n=2,4,6,10）分子的平均反应热在n=6处为极大值,说明C₆₀（CF₃）₆应该是最容易得到的加成产物.由Mulliken电荷可知,加成的CF₃个数越多,CF₃与笼子的相互作用也就越强,每个CF₃转移到笼子上电荷数也就越多.C₆₀（CF₃）_n的自旋聚居数分布表明它们均为闭壳层结构.最后,从CF₃对分子的前线轨道贡献可知,四种分子的得电子情况和失电子情况均发生在碳笼本身,并不随着CF₃个数的增加而发生明显的改变. 关键词： 60（CF₃）_n （n=2')" href="#">C₆₀（CF₃）_n （n=2 10） 几何结构和电子性质 密度泛函     

微波电子回旋共振等离子体增强化学气相沉积法沉积氟化非晶碳薄膜的研究

使用三氟甲烷和苯的混合气体,利用微波电子回旋共振等离子体增强化学气相沉积法制备了F/C比在0.11—0.62之间的α-C∶F薄膜.研究了微波功率对薄膜沉积和结构的影响,发现微波功率的升高提高了薄膜的沉积速率,降低了薄膜的F/C比,也降低了薄膜中CF和CF₃基团的密度,而使CF₂基团的密度保持不变.在高微波功率下可以获得主要由CF₂基团和C=C结构组成的α-C∶F薄膜.薄膜的介电频率关系(1×10³—1×10⁶Hz)和损耗频率关系(1×10²—1×10⁵Hz)均呈指数规律减小,是缺陷中心间简单隧穿引起的跳跃导电所致.α-C∶F薄膜的介电极化主要来源于电子极化 关键词： 氟化非晶碳薄膜 ECR等离子体沉积 键结构 介电性质     

AlHn(n=1—3)的分子结构和AlH3热力学稳定性

在gaussian03基础上，分别用b3lyp和qcisd方法，在6-311++g^**基组水平上研究了AlH_n(n=1—3)分子及其一价阴阳离子的几何结构和谐振频率，计算了它们中性分子的离解能，第一垂直电离能，电子亲和能. 并与可能得到的实验值及文献上的理论计算值进行了比较. 发现qcisd方法得到的数据更接近实验值. 计算发现对AlH，AlH₂和AlH₃分子及其1价阳离子的Al—H键长，随着H原子数的增多，键长越短， 关键词： 3分子')" href="#">AlH₃分子 平衡几何结构 垂直电离能 垂直电子亲和能     

氟利昂F113分子在飞秒激光作用下的多光子电离解离动力学

大气臭氧层因吸收太阳紫外光, 是人类必不可少的保护伞. 氟利昂在太阳光辐射下解离生成破坏臭氧的游离态氯原子, 是破坏大气臭氧层的主要元凶之一. 本文利用飞行时间质谱技术和离子速度成像技术研究了氟利昂F113(三氟三氯乙烷)分子在800 nm 飞秒光作用下的多光子电离解离动力学. 利用飞行时间质谱探测技术, 得到了三氟三氯乙烷在该波长飞秒激光作用下发生多光子电离解离产生的碎片质谱. 通过荷质比对碎片质谱进行了详细的标定和分析. 在质谱上未发现母体离子, 所有观察到的离子都是由于激光脉冲作用下产生的碎片. 三个最主要的碎片离子是CFCl₂⁺, CF₂Cl⁺, C₂F₃Cl₂⁺. 通过飞行时间质谱标定, 发现并归属了多个解离通道. 三个主要的解离机理分别为: 1) C-Cl键断裂直接生产氯自由基的通道C₂F₃Cl₃⁺→C₂F₃Cl₂⁺+Cl; 2) C--C键断裂C₂F₃Cl₃⁺→CFCl₂⁺+CF₂Cl; 3) C--C键断裂C₂F₃Cl₃⁺→CF₂Cl⁺+CFCl₂. 利用离子速度成像技术对这三个主要通道产生的碎片离子进行成像, 得到了C₂F₃Cl₂⁺, CFCl₂⁺和CF₂Cl⁺离子的速度影像. 由C--Cl键断裂产生的碎片离子C₂F₃Cl₂^{+}的速度分布由两个高斯分布曲线拟合, 而由C--C键断裂产生的碎片离子CFCl₂⁺和CF₂Cl⁺可以用一个高斯曲线拟合. 通过影像分析得到了解离碎片的平动能分布和角向分布各向异性参数等详尽的动力学信息. 结合高精度密度泛函理论计算对解离动力学进行了进一步的分析和讨论.深入认识氟利昂的解离动力学可为进一步控制破坏臭氧层提供理论参考和实验依据.     

332—362nm范围内CF2Cl自由基的共振增强多光子电离研究

用CF₂Cl₂分子直流脉冲放电的方法产生CF₂Cl自由基，结合共振增强多光子电离(REMPI)技术，测量了332—362nm波长范围内CF₂Cl自由基的(2+1)REMPI光谱，分析并标识了4s Rydberg态带源位于(ν_0—0=55371cm^-1)，两个被激活振动模ω′₃(CF₂剪式振动模)和ω₄′(OPL 关键词：     

NH3分子在LiH（100）表面吸附的第一性原理研究

采用第一性原理方法研究了NH₃分子在LiH（100）晶面的表面吸附情况.通过研究LiH（100）/NH₃体系的吸附位置、吸附能和电子结构,发现NH₃分子在LiH（100）晶面主要是化学吸附,初始位置为NH₃分子中N-H键在Li顶住时失去一个H原子,并在LiH（100）面形成NH₂基,其吸附能为0.511 eV,属于强化学吸附,吸附作用最强.此时NH₂基与附近H原子和Li原子之间为离子键作用,NH₂基中N—H键为共价键;NH₃分子中另一个H原子与LiH表面的一个H原子形成一个H₂分子逸出表面.H₂分子中H-H键为明显的共价键.     

两种烷基碘化物分子C—I键解离的从头计算

分别采用多组态自洽场方法和二阶多组态准简并微扰论方法,计算了烷基碘化物分子CF₃I和C₂H₂F₃I沿C—I键的绝热势能曲线和垂直激发能. 结果发现,这两种分子的低激发态均为排斥态;基态的解离能分别为2.473eV和2.835eV,其中前者与实验结果符合较好. 关键词： 烷基碘化物分子 解离能 势能曲线     

分子部分电子态的高阶振动能级和离解能的精确研究

鉴于K₂分子电子态的振动能谱和分子离解能D_e在实际研究和应用中的重要性,应用Sun,Ren等人提出的基于微扰理论的代数方法(AM)和基于AM的代数能量方法(AEM)研究了K₂分子的X¹Σ⁺_g,a³Σ⁺_u,0^-_g,B¹Π_{u< 关键词： 2}分子')" href="#">K₂分子 代数方法 高阶振动能级 离解能     

Laser isotope separation of 13C: A comparative study

IR laser chemistry of (CF₃Br/Cl₂) mixture and neat CF₂HCl are examined in the context of ¹³C enrichment. Decomposition extent, enrichment factor and energy absorbed are measured for both systems at their respective optimum conditions. A direct comparison is obtained by keeping extraneous factors such as laser, its pulse duration, cell, irradiation geometry etc. the same. The halogen scavenged CF₃Br MPD requires lower fluence compared to neat CF₂HCl irradiation. Overall throughput for a product with 60–65% ¹³C content in a single stage is the same for both systems requiring a similar amount of energy. However, at lower enrichment levels, CF₂HCl MPD is better than (CF₃Br/Cl₂) photolysis in terms of both product yield and energy absorption.     

Frequency dependent kinetics of the cw CO2 laser induced reaction of CF3Br

Kinetics of the decomposition of CF₃Br at 20 torr by a cw CO₂ laser have been studied over the range of laser frequencies 1043–1085 cm^-1. At constant translational temperature the change in the rate constant with laser frequency over the frequency range is a factor of 500, comparable to the effect previously observed in CF₂ClCF₂Cl and CF₃CF₂Cl. Arrhenius plots show an activation energy of 64.9 kcal/mole, independent of frequency. The laser induced optical absorption of CF₃Br exhibits a hysteresis effect at the lower laser frequencies.     

Excitation and dissociation of polyatomic molecules under the action of femtosecond infrared laser pulses

The effect of high-intensity femtosecond laser pulses (100–200 fs) in the near (0.8–1.8 μm) and medium (4.6–5.8 μm) IR ranges on the CF₂HCl, CF₃H, (CF₃)₂C=C=O, and C₄F₉COI molecules is examined. Irradiation of CF₂HCl and CF₃H molecules by 0.8-to 1.8-μm laser pulses with intensities of >40 TW/cm² (>4 × 10¹³ W/cm²) makes them dissociate to yield CF₃H and CF₄, respectively. The key mechanism of the dissociation of these molecules is field ionization and fragmentation. The excitation of the stretching vibrations of the C=O bond in the (CF₃)₂C=C=O and C₄F₉COI molecules by 4.5-to 5.8-μm femtosecond pulses produced no detectable dissociation up to a fluence of ∼0.5 J/cm² (or a intensity of ∼2.5 TW/cm²). Probable explanations of this observation are discussed. Original Russian Text ? V.M. Apatin, V.O. Kompanets, V.B. Laptev, Yu.A. Matveets, E.A. Ryabov, S.V. Chekalin, V.S. Letokhov, 2007, published in Khimicheskaya Fizika, 2007, Vol. 26, No. 4, pp. 18–25.     

Interaction of 157-nm excimer laser radiation with fluorocarbon polymers

Two important fluoropolymers, polytetrafluoroethylene [PTFE—(C₂F₄)_N] and polyvinylidene fluoride [PVDF—(C₂H₂F₂)_N], respond to 157-nm laser radiation in dramatically different ways. At fluences sufficient to produce rapid etching, the volatile emissions from PTFE are dominated by (CF₂)_N fragments. The velocities of the fastest (CF₂)_N molecules at each mass are consistent with kinetic energies on the order of an electron volt—and change little with fluence. This fluence independence suggests that the velocities are not affected by collisions after emission. To account for the high kinetic energies and the unusual, half-monomer mass distribution, we propose that these fragments are produced by photochemical scission of the polymer backbone, and that a fraction of the excitation energy is delivered to each fragment as kinetic energy. In contrast, the principle neutral species from PVDF is HF. HF is produced by the scission of C-F bonds, followed by chemical reactions with nearby hydrogen. This process is accompanied by the conjugation of backbone C-C bonds. The photochemical cleavage of C-C bonds in PTFE and C-F bonds in PVDF is consistent with the lower C-C bond energy of PTFE.     

Improved isotope separation in laser dissociation of trifluoromethyl halides: Scavenging of CF3 with HI

The efficiency of¹³C isotope separation by multiphoton dissociation using a CO₂ laser has been shown to increase by ∼33% upon addition of small amounts of HI to the starting mixture. The reason for this increase is that the CF₃ radicals are scavenged by HI more rapidly than they recombine with free iodine atoms to reform the starting material. For Torr and for 0.5J/cm² roughly 65% of the CF₃ and I radicals reform the starting material in the absence of HI. The results of this study indicate that at −80°C the rate constants for CF₃+CF₃→C₂F₆ and CF₃+I→CF₃I are about equal and are roughly 8 times higher than that for CF₃+HI→CF₃H+I.     

Direct observation of the vibrational energy redistribution in (CF<Subscript>3</Subscript>)<Subscript>2</Subscript>CCO molecules resonantly excited by femtosecond infrared laser radiation

The dynamics of multiphoton excitation of (CF₃)₂CCO molecules has been investigated under the condition of resonant action of femtosecond infrared laser radiation on the ν₁ vibrational mode of the C=C=O bond. It has been shown that the mode-selective excitation of this vibration occurs up to the ν = 6 level. The kinetics of the subsequent intramolecular vibrational energy redistribution from the ν₁ mode has been measured. A value of 5 ± 0.3 ps has been obtained for the characteristic time of this process.     

Laser-pumped molecular laser

The parameters of laser-pumped molecular lasers are investigated. It is established that the energy and tuning characteristics of an NH₃ laser (E_g = 1.5 J, efficiency 20%, P_av = 20 W, radiation frequency tuning band 753–890 cm^-1) are decisively influenced by the addition of N₂. A focusing raster optical-pumping system has made it possible to obtain a specific lasing energy 12 J/liter. A CF₄ laser with lasing energy 40 mJ operates in the 612–655 cm^-1 band. Experiments on dissociation of the molecules CCl₄ and UF₆ were carried out with the aid of NH₃ and CF₄ lasers. The systems and methods of producing Raman lasers (RL) are presented. An effective RL amplifier on rotational transitions in compressed H₂, which transforms tens of beams of Nd lasers into one coherent beam of the first Stokes component with λ ? 1.13 μm at an efficiencyup to 70%, is described.     

Isotopically selective infrared multiphoton dissociation of 2-chloro-1,1,1-trifluoroethane: 13C selectivity and mechanism

13 C-selective infrared multiphoton dissociation of CF₃CH₂Cl has been studied by analyzing the distribution of ¹³C concentrations of the main products CF₂=CHCl, CF₂=CH₂, CF₂=CHF, C₂F₆, and the trace products CF₃CH₂CF₃ and CF₃CH=CHF₃. The mechanism mainly concerns the dissociation of energized CF₃CH₂Cl, the collisional stabilization of excited CF₃CH and CF₃CH₂ and the recombination of the nascent radicals. No significant radical–molecule reactions degrade the intrinsic ¹³C dissociation selectivity. High ¹³C production yield and ¹³C concentration can be attained at a laser fluence of 1.6 J/cm². Such low fluence can be used to improve focus condition and enhance photon utilization efficiency for practicable ¹³C separation. Received: 10 March 1998/Revised version: 17 September 1998     

Features of kinetic processes in the active medium of a pulsed chemical oxygen-iodine laser

Conclusion It can be concluded from our experiments and calculations that the product CF₃O₂ of the interaction between the CF₃ radical and the O₂ molecule quenches the oxygen O₂(¹) more strongly. At low chlorine admixture density in the singlet-oxygen stream this output energy of the oxygen-iodine laser with CF₃I as the atomic iodine donor is lower compared with CH₃I. The rate constant of quenching singlet oxygen by CF₃O₂ molecules is (3–5)·10^–11 cm³·sec^–1. It would be possible to decrease the influence of CF₃O₂ by adding to the initial O₂ ^*–O₂–CF₃I–Ar active mixture some other substance causing the CF₃ radicals to enter in a chemical reaction with a shorter characteristic time than that for CF₃O₂ formation. Of course, neither the initial substance nor the reaction products should quench O₂ ^* noticeably. This role can be possibly assumed by the NO molecule.The influence of the chlorine additive on the output energy of a laser with CH₃I and CF₃I differs greatly. The choice of the chlorine donor must therefore be determined by the amount of this additive. CH₃I is preferable if the chlorine is fully utilized in the singlet-oxygen laser, and CF₃I in the opposite case.Quantum Radiophysics Division, Lebdev Physics Institute. Translation of Preprint No. 21 of the Lebedev Physics Institute, Moscow, 1991.