【作者】 赵东锋；

【导师】 陈旸；

【作者基本信息】 中国科学技术大学 ， 物理化学， 2009， 博士

【摘要】 自由基在燃烧过程、大气化学、分析化学等众多领域中都扮演着重要的角色,自由基光谱研究对于了解自由基微观结构、发展检测手段、确认化学反应通道及分支比等方面都有重要的意义。本论文的主要工作是设计和搭建了一套用于研究自由基光谱的光腔衰荡光谱(CRDS)实验装置,并将之与超声射流冷却、气体放电等技术相结合,研究了PH2、AsH2以及过渡金属自由基的吸收光谱。主要工作和研究成果有：实验装置的建立我们设计并搭建了一套流动体系中脉冲直流空心阴极放电-光腔衰荡光谱实验装置(Pulsed DC Hollow Cathode Discharge-CRDS)。在这套装置中,我们引入了双阳极空心阴极放电作为目标自由基产生源。除了建立这套装置外,我们还将光腔衰荡光谱测量系统与实验室原有的超声射流腔体结合,改造成超声射流-脉冲直流辉光放电-光腔衰荡光谱装置(Supersonic jet-Pulsed DC Glow Discharge-CRDS).通过测量高反镜反射率和H20的泛频吸收光谱两个实验验证了我们的光腔衰荡光谱测量系统的可行性：吸收的检测限可达4×10-3(1-R)；获得的吸收光谱的光谱分辨率优于0.055cm’。PH2自由基光谱研究在超声射流条件下,通过对PH3、SF6与Ar的混合气脉冲直流辉光放电产生PH2自由基,利用光腔衰荡光谱技术和激光诱导荧光技术获得了PH2自由基在410-555nm范围内的光谱。在光谱中总共观测到10个振动带,它们被归属为PH2-自由基j2A1-X2B1跃迁的弯曲振动激发000&20n(n=1-6)和2ln(n=1-3)的两个序列。通过对CRDS光谱的转动分析和振动分析,确定了PH2自由基X2B121态和A2Al2n(n=0-4)态更为完整和更为精确的光谱常数,包括带源、转动常数、离心畸变常数、自旋转动常数以及A2A1态弯曲振动参数等；改进了X2B121态和A2A12n(n=0-3)态的转动项值；分析了A2A12n(n=0-6)态所受到的扰动。通过对转动谱线的荧光寿命的测量,获得了A2A12n(n=0-6)态的自由寿命。通过对CRDS实验和LIF实验结果的对比分析,讨论了PH2自由基A2A1态的扰动源以及可能存在的预离解通道。AsH2自由基光谱研究在超声射流条件下,通过对AsH3、SF6与Ar的混合气脉冲直流辉光放电产生AsH2自由基,利用光腔衰荡光谱技术和激光诱导荧光技术获得了AsH2自由基在380-510nm范围内的光谱。在光谱中总共观测到11个振动带,它们被归属为AsH2自由基A2A1-X2B1马跃迁的弯曲振动激发000&20n(n=1-7)和21n(n=1-3)的两个序列。通过对实验光谱的转动分析和振动分析,确定了AsH2自由基X2B121态和A2A12n(n=0-7)态更为完整和更为精确的光谱常数,包括带源、转动常数、离心畸变常数、自旋转动常数以及A2A1态弯曲振动参数等,其中绝大大部分的数据为首次实验获得；首次实验确定了X2B121态和A2A12n(n=0-7)态的转动项值。通过对五A2A1-X2B120n(n=2-7)带转动谱线线宽的研究,获得了A2A12n(n=2-7)各态的自由寿命。综合转动分析和激发态自由寿命的结果,分析了A2A12n(n=0-7)态所受到的扰动,并提出了AsH2自由基A2A1态三个可能的预离解通道。我们还在室温下利用空心阴极放电结合CRDS技术研究了AsH2自由基A2A1-X2B1跃迁000带的吸收光谱,获得了一些高阶光谱参数,如六阶和八阶离心畸变常数和四阶自旋转动相互作用常数,并对00态较高转动能级受到的扰动进行了讨论。CRDS结合空心阴极放电研究过渡金属自由基光谱设计了一套双阳极空心阴极放电装置作为过渡金属自由基的产生源,并将之与光腔衰荡光谱(CRDS)技术相结合,用于研究过渡金属自由基的吸收光谱。借助于光学谐振腔的腔镜和放置于光电倍增管前的窄带通滤色片,我们基本消除了等离子体自身光辐射的影响。通过对实验获得的CuF B1∑+-X1∑+跃迁、CuBrb3Π+-X1∑+跃迁的吸收光谱的分析,得出整套实验系统的性能为：吸收检测灵敏度为-4×10-7,光谱分辨为-0.055cm-1。更多还原

【Abstract】 The free radicals play an important role in many fields, such as combustion process, atmosphere chemistry, and analytical chemistry, et al.. The spectroscopy of free radicals can provide important information in understanding their structures, detecting them, and identifying the mechanisms and branch ratios of related chemical reactions. The main contributions presented in this dissertation are a newly built cavity ringdown spectroscopy (CRDS) apparatus, and the spectroscopy study on the PH2, AsH2 and transition metal containing radicals, by using CRDS combined with the technique of gas discharge both in flow system and supersonic molecule beam.Building the experimental apparatusA pulsed CRDS apparatus used to study spectra of radicals in the flow system was designed and assembled. The hollow cathode discharge with double anodes was employed to produce target radicals. By the experiments of measuring the reflectivity of cavity mirrors and the absorption spectra of H2O, the reliability of the CRDS apparatus was verified:an absorption detection limit of 4×10-3(1-R), and the spectral resolution of less than 0.06 cm-1 in the obtained spectra.In another apparatus used in this dissertation, was built by installing the CRDS apparatus to an old vacuum chamber which was used to produce the supersonic molecule beam in our lab. The pulsed DC discharge under the nozzle was used to produce target radicals in this apparatus.Spectroscopy study of the PH2 radicalThe absorption spectra of jet-cooled PH2 radicals were recorded in the wavelength range of 410-555 nm by CRDS. The PH2 radicals were produced in a supersonic jet by pulsed DC discharge of a mixture of PH3 and SF6 in argon. Ten vibronic bands with fine rotational structures have been observed and assigned as the 000,20n(n=1-6), and 21n(n=1-3) bands of the A2A1-X2B1 electronic transition. From the rotational and vibrational analysis, the molecular parameters, including rotational constants, centrifugal distortion constants, spin-rotation interaction constants and vibrational constants for X2B121andA2A1 2n(n=0-4)states, were determined with reasonably high precision. In addition, large perturbations observed in each Ka level of the excited vibronic states were briefly discussed. The lifetimes of the rot-vibronic levels in A2A1 state of PH2 were obtained by measuring the fluorescence decay rate using laser induced fluorescence (LIF) technology. Based on the comparison of the spectra obtained by LIF and CRDS, respectively, and the obtained lifetimes of the rot-vibronic levels, the perturbations in the A2A1 state and the possible predissociation of PH2 were discussed.Spectroscopy study of the AsH2 radicalThe absorption spectra of jet-cooled AsH2 radical were obtained in the wavelength range of 380-510 nm by CRDS. The AsH2 radicals were produced in a molecular beam of a mixture of AsH3, SF6, and argon. Eleven vibronic bands with fine rotational structures have been identified and assigned as the 000,20n(n=1-7), and 21n (n=1-3) bands of the A2A1-X2B1electronic transition. Based on the previous studies of AsH2 radical, rotational assignments and rotational term values for each band were obtained, and the molecular parameters including vibrational constants, rotational constants, centrifugal distortion constants, and spin-rotation interaction constants were also determined with reasonably high precision. By investigating the spectral linewidths of the rotational lines in each band, the lifetimes of the rot-vibronic levels in A2A1 state was obtained, and the predissociation dynamics in the A2A1 state of AsH2 radical were discussed in detail.We also studied the A2A1-X2B1 000 band of AsH2 in the room temperature by CRDS. The AsH2 radicals were produced by the hollow cathode discharge of AsH3/Ar. Several high order spectra parameters in A2A1 00 state were obtained, and the perturbations in the higher rotational levels in A2A1 00 state were briefly discussed. Pulsed CRDS on the transition metal containing radicals in hollow cathode discharge plasmaThe cavity ringdown spectroscopy combined with hollow cathode discharge plasma is presented for the absorption spectroscopy study on the transition metal containing radicals. The performance is demonstrated with the spectra of the CuF B1∑+-X1∑+transition and the CuBr b3(?)+-X1∑+transition. Rotational resolved spectra with the spectral linewidth of the order of 0.055 cm-1 have been obtained in the room temperature. The absorption detection limit can be up to the order of-4×10-7 absorption.更多还原