CF_3I在强红外场下的多光子解离

本文用TEA CO_2激光9.6R(14)支作激发光源,富里叶变换红外光谱仪作分析手段,NO,O_2作CF_3自由基的捕捉剂,研究了CF_3I红外多光子解离的动力学。实验发现,O_2和NO均可用来捕捉CF_3I的红外光解产物CF_3自由基。从对CF_3I的红外多光子解离率与外加气体压力的变化关系的研究,以及CF_3I红外多光子吸收的测量,揭示出该分子在受红外激光激发时,具有小分子的特性。同时也观察到外加气体对早期瓶颈效应的消除。在无碰撞及早期瓶颈效应可忽略状态下,用能量间隔主方程对多光子解离率与激光能量密度的变化关系作了拟合,得出了与实验比较一致的结果。     

CF_2HCl分子在红外多光子解离时分子间的能量传递过程

分子在强红外激光照射下可以吸收几十个红外光子而解离,目前人们已经对这一现象进行了广泛的研研。其中研究较多的分子有SF_6、CF_3I、CF_2HCl等。由于CF_2HCl分子在红外激光照射时解离过程比较简单,而且也是一个激光分离碳-13同位素有前途的工作介质,人们对CF_2HCl分子的红外多光子解离规律做了较深入的研究。Y.T.Lee等利用分子束的方法研研了CF_2HCl分子在红外多光子解离时的机制。J.C.Stephenson等以及R.D.Duperrex等测定了CF_2HCl分子在无碰撞条件下的瞬时解离规律,认为CF_2HCl分子具有明显的转     

激光引发二氟卡宾与烯烃的反应

近十年来,激光引发一氯二氟甲烷红外多光子解离和激光敏化反应的研究非常活跃,但大部分工作都集中于解离机制及同位素分离,而对CF_2HC(?)多光子解离产生的二氟卡宾     

杂环化合物的红外多光子解离机理的研究

采用TEA CO_2激光器研究了1,4-二氧六环、吡咯烷和噻吩等杂环化合物的红外多光子解离过程,探讨了解离机理,给出解离率与激光能流的关系。解离阈值分别为0.85、1.0、1.5J/cm~(-2)。     

无氧条件下Pd/CeO2催化剂表面NH3还原NO过程中N2O形成机理研究

氮氧化物(NO_x,主要包括NO和NO_2)是主要的大气污染物之一,造成酸雨,光化学烟雾和臭氧层破坏等环境问题,甚至直接危害人体健康.化石燃料燃烧和汽车尾气排放是NO_x的主要来源,严格控制火力发电厂,大型锅炉,汽车尾气等污染源中NO_x的排放刻不容缓.以NH_3为还原剂选择性催化还原NO_x(NH_3-SCR)是目前公认的最有效的NO_x脱除技术,然而在催化NO_x还原为N_2的过程中往往伴随着副产物N_2O的生成,降低了催化剂的选择性,造成温室气体效应和破坏臭氧层等环境问题.因此充分理解NH_3-SCR过程中N_2O的形成机理对于抑制N_2O的产生、提高催化剂的选择性十分重要.本文将高度分散的Pd纳米团簇负载在Ce O_2纳米棒上制成Pd/Ce O_2催化剂,结合NH_3-TPD, NO-TPD和原位傅里叶转换红外光谱等表征手段研究了无氧条件下该催化剂上利用NH_3催化还原NO过程中N_2O的产生路径.结果表明, N_2O的形成途径与反应温度和反应气体的浓度相关.当反应气体中NH_3含量大于化学计量比时,在反应温度低于200°C时,由NH_3活化产生的吸附态H·自由基与催化剂表面吸附的NO反应先生成中间产物HON,两个HON分子进一步反应生成N_2O;过量的吸附态的H·自由基也可以与HON反应生成N_2,所以低温下(200°C)随着反应气氛中NH_3的增加,解离生成的H·也随之增加,促进反应向着生成N_2的方向进行,从而抑制了N_2O的产生.随着反应温度增加, NH_3解离产生的H·被CeO_2表面的O捕获形成羟基,中间产物HON的生成被切断,从而阻断了N_2O的生成.同时由于体系中含有大量的NH_3,吸附态的NO会优先与活化态的NH_3物种反应生成N_2,阻碍了NO解离生成N_2O这一过程的发生,因此NH_3过量情况下在高温下观察不到N_2O的产生,可获得100%的N_2选择性.但是当反应气体中的NH_3含量不足时,即体系中含有过量的NO,当反应温度高于250°C, NO可在催化剂表面解离生成吸附态的N·自由基和O·自由基, N·自由基可进一步与吸附态的NO反应生成N_2O, NO的解离是N_2O生成的速控步,还原性吸附物种对O·自由基的捕捉将有利于N_2O的生成.当反应温度介于200–250°C, NH_3解离产生的H·自由基既可以与NO结合生成HON中间产物,又能被CeO_2表面的O捕获形成羟基,两个反应之间存在竞争,此时N_2O产生与反应气体浓度之间的关系不再呈单调变化.     

CF_3Br的红外光化学和光物理

本文报道本实验室在CF_3Br的激光光声及光热光谱,CF_3Br单分子光化学反应的动力学及碳同位素分离等三方面的最新结果,并与前人工作做了比较。实验中我们用自制的光声、光热探测器测量了CF_3Br的红外多光子吸收(MPA)过     

CF_3I催化合成中氟夺取途径的密度泛涵理论研究

CF_3I在制冷剂、刻蚀剂、发泡剂、灭火剂以及有机氟工业等领域具有广泛的应用.在活性炭负载碱金属盐的催化下,以CHF_3和碘为原料,可直接合成CF_3I.CF_3及CF_4分别是该反应过程中重要的中间产物和副产物,而积碳则导致催化剂失活的重要原因.因此研究它们的产生机理具有重要意义.对此本文采用密度泛涵理论(DFT)方法进行了研究.结果表明:CF_2及CF_3可以对吸附于graphite(001)表面的CFCF_3进行多步氟夺取,最终得到CF_3、CF_4以及C_2自由基.以上氟夺取反应产生的C_2自由基也导致了实验中的积碳现象.上述反应机理与现有的实验数据相符.     

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.     

二氧化碳激光引发2-氯-1,1,1,2-四氟乙烷反应

本文研究了用TEA-CO_2激光和CW-CO_2激光以SF_6作为敏化剂引发CF_3CFHCl的反应。分析了CF_3CFHCl以及添加清除剂Cl_2,Br_2,O_2,的光解产物。结果表明CF_3CF:是初级产物,它很易重排成为CF_2—CF_2,或转化成CF_3CF—CF_2。在Cl_2或Br_2存在时,可生成CF_3CFCl_2或CF_3CFBr_2。此外,还讨论了反应机制。     

多氟烯烃和炔烃的钯催化氢化

本文报道Pd/Al_2O_3(1%)催化剂催化氢化CF_3CCl=CClCF_3,CF_3CCI==CHCF_3和CF_3C=CCF_3等多氟烯烃和炔烃的结果。经1~H和(19)~F核磁共振、质谱、红外等分析,证明了用制备色谱分离后的氢化产物主要成份的结构。前二者的氢化产物中主要是CF_3CH_2CH_2CF_3和CF_3CH_2CHClCF_3的混合物,而CF_3C=CCF_3氢化后只生成CF_3CH_2CH_2CF_3。     

CF2HCl分子在红外多光子解离时分子间的能量传递过程

The infrared multiphoton dissociation (IR MPD) of CF_2HCl by measuring the C_2F_4 product after laser irradiation is investigated, The dissociation fraction of CF_2HCl as a function of the CF_2HCl pressure, laser energy fluence and number of laser pulses is measured. Under the low pressure condition the bottleneck effect is observed. Under the collision condition the dissociation fraction of CF_2HCl is affected by the competition between rotaional hole filling (collisional repoputation of pumped rotational states) and collisional deactivation of excited CF_2HCl moleculae.     

Direct measurement of CF3I multiphoton dissociation yield by iodine-laser detection of iodine atoms

The primary yield of CF₃I multiphoton dissociation under CO₂-laser irradiation has been determined by direct monitoring of iodine atoms using a pulsed iodine laser. The primary yield was found to exceed markedly an observed MPD yield obtained from measurement of the CF₃I consumption not only in CF₃I-N₂ but also in CF₃I-O₂ mixtures.     

CF3Br的红外光化学和光物理

We present the optothermal and optoacoustic spectra of CF_3Br in TEA CO_2 laser 00°1—02°0 R branch. Three absorption peaks has been observed at R(14) line (1074.6 cm~(-1)), R(18) line (1077.3cm~(-1)), and R(22) line (1079.9cm~(-1)) respectively. The peak at R(22) coincides with the position of P branch of CF_3Br linear IR spectrum, but two peaks at R(14) and R(18) can be interpreted as the hot bands.We also studied the multiphoton dissociation of CF_3Br and carbon isotope seperation.     

15N isotope-selective infrared multiphoton dissociation of nitromethane by a free electron laser

Successful experiments on the isotope-selective infrared multiphoton dissociation (IR MPD) of nitromethane molecules in the region of stretching vibrations of the NO₂ group have been performed for the first time under IR free electron laser (FEL) irradiation in a mixture with the natural content of the¹⁵N isotope of 0.4%. The content of the¹⁵N isotope in the products of NO dissociation varies within 0.1–1.6% as a function of the laser radiation frequency. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 739–742, April, 1998.     

连续二氧化碳激光敏化CFHCl~2反应

本文报道了连续二氧化碳激光敏化CFHCl_2,CFHCI_2+O_2和CFHCl_2+Cl_2的反应,分析了反应产物并讨论了反应机制。利用激光敏化反应,在气相中可以产生CFCl卡宾,此外,在激光敏化氧化和氯化CFHCl_2和CF_2HCl[1]中,反应产物CFClO,CF_2O,CFCl_3a和CF_2Cl_2的产率几乎定量。     

Laser-Induced Luminescence upon IR Multiphoton Excitation of Triethylsilane

A comparative study of the effect of IR laser radiation frequency on the yield of secondary reactions and luminescence intensity as functions of the laser pulse energy upon IR multiphoton dissociation of triethylsilane was performed. It was found that the reaction and luminescence threshold energies symbatically increase on passing from a frequency of 985 to 944 cm^–1. Based on experiments with xenon admixture to triethylsilane, it was concluded that the diethylsilyl radical, the product of the primary reaction of C–Si bond dissociation, plays the major role in the reactions of formation of luminescent species.     

Multiphoton infrared laser photochemistry of polyatomic molecules: (CF3)3 Cl

Both the primary and resulting yields of the multiphoton dissociation (MPD) of (CF₃)₃Cl upon CO₂-laser irradiation are found to depend strongly on the CO₂-laser radiation frequency. The consecutive multiphoton fragmentation of (CF₃₃C radicals produced in the MPD of (CE₃)₃Cl is shown to occur at several laser frequencies during the same CO₂-laser pulse. The increase in the isotopic selectivity of the overall MPD process due to multiphoton fragmentation and hence the possibility of selective MPD at higher pressures are discussed.     

Multiphoton dissociation of C3F6O

Major characteristics of multiphoton absorption and multiphoton dissociation of hexafluoropropene oxide (HFPO) were studied. Spectral relationships of the average number of IR photons absorbed per molecule and the yield of multiphoton dissociation were determined in the range of 1040-985 cm^–1 at different laser fluences. At the laser line 1025.3 cm^–1, the effect of collisions with buffer gases on the HFPO multiphoton absorption and multiphoton dissociation was studied and theq-factor was determined (q = O.6 at= 0.55J cm^–2). Characteristic features of HFPO decomposition under collisional conditions (p _HFPO> 0.1 Torr) were discussed. An anomalous difference in the values for quantum efficiency of multiphoton dissociation for long-wave and short-wave wings of HFPO absorption band was revealed. A procedure for correlating the experimental and theoretical data on the yield of multiphoton dissociation (when theq-factor is unknown) was suggested, and corresponding calculations were performed for the frequency 989.6 cm^–1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1927–1932, November, 1994.