SF_6-UF_6体系中六氟化铀的振动弛豫研究

本文以脉冲CO_2激光激发SF_6,经碰撞再使UF_6分子激发,通过测定振动受激UF_6的紫外吸收变化,研究了六氟化铀分子的振动弛豫过程。对于2.0.Torr SF_6+2.0Torr UF_6体系,在220-320 nm范围内测定了UF_6的紫外吸收信号随时间的变化,测得UF_6三类不同振动受激态分子间的V-V能量弛豫时间分别为6.8,9.0和26μs,相应的V-T能量弛豫时间为42,8和1ms。此外,还讨论了SF_6-UF_6体系中振动能量弛豫的机理。     

SF6-UF6体系中六氟化铀的振动弛豫研究

本文以脉冲CO_2激光激发SF_6, 经碰撞再使UF_6分子激发, 通过测定振动受激UF_6的紫外吸收变化, 研究了六氟化铀分子的振动弛豫过程。对于2.0. Torr SF_6+2.0 Torr UF_6体系, 在220-320 nm范围内测定了UF_6的紫外吸收信号随时间的变化, 测得UF_6三类不同振动受激态分子间的V-V能量弛豫时间分别为6.8, 9.0和26 μs, 相应的V-T能量弛豫时间为42, 8和1 ms。此外, 还讨论了SF_6-UF_6体系中振动能量弛豫的机理。     

氟磺酸氟振动光谱的从头算

采用从头算HF／SCF方法以6-31G基组研究了FOSO2F分子的几何结构、振动谐性力场和红外光谱强度．理论力场由Pulay的标度量子力学方法进行标度,计算得到的振动频率与实验值比较平均偏差为6．3cm-1．根据振动频率的势能分布和从头算红外光谱强度值对此分子的振动基频进行了理论归属．     

SF_6在低温Ar基体中的红外光谱研究

基体隔离红外光谱已被广泛用于研究不稳定分子和离子的光谱,而且对研究分子间的相互作用也是十分重要的。SF_6在Ar基体中的v_3谱的测定,前人只观察到SF_6单体的谱带。至于SF_6的簇合物,除了在超声分子束中发现(SF_6)_2和(SF_6)_3有存在的可能性之外,至令尚未见报道。本文采用多微孔喷咀和连续沉积法,在低温(10—30K)条件下用傅里哀变换红外光谱仪测定SF_6在Ar基体中的光谱,并通过改变SF_6与Ar的配比以及升温扩散测定SF_6聚集体的谱     

石墨烯分子振动模式因子群分析与密度泛函计算

运用因子群分析法对石墨烯的分子振动模式进行了理论分析,得到石墨烯的分子振动模式,计算出各振动模式的光谱特性.对所建立的石墨烯晶体的布拉维单胞模型采用基于密度泛函理论的第一性原理进行分子振动频率与模式的计算,所得的振动模式数目以及各振动频率的光谱特性同因子群分析方法所得结论一致.结合上述计算结果,通过系统比较石墨与石墨烯之间的红外光谱和拉曼光谱的差别,从理论上解释了具有D6h对称的石墨烯的A2u、E1u红外活性特征振动模式没有在红外光谱中出现的原因.     

红外激光诱导SF6与硅和钨的表面化学反应

本文研究了TEA CO_2激光诱导SF_6与单晶硅和金属钨的表面化学反应。实验结果表明这些反应的反应率与激光频率之间具有明显的依赖关系, 在频率为942.2 cm~(-1)处反应率呈极大值。对于SF_6-Si体系, 反应率与硅的不同晶面有关, 在相同条件下Si(100)面与SF_6的反应率大于Si(111)面。对于SF_6-W体系, 测定了激光能量密度和脉冲辐照次数与反应率之间的关系, 其反应阈值为1 Jcm~(-2), 并测得该反应的速率与SF_6分压呈一级反应关系。同时, 还讨论了上述反应的机理, 认为气态振动受激的六氟化硫分子与被激光激活的固相表面之间的相互作用是反应的主要过程。     

激光诱导荧光衰减探测光化学反应

激光荧光光谱为重要光谱分析手段之一,广泛用于物理、化学、生物学等研究领域。 但对于一些含有发色基团的大有机分子,由于分子振动自由度很大,振动能级连续分布, 其荧光谱成为宽展的光谱带,振动带结构不复存在,使荧光光谱难于用作样品的成份鉴定。对于溶液样品由于分子间的碰撞及长程力的作用,也可能造成荧光猝灭和分子间电 子能量转移,特别是对那些吸收光子后易发生光分解的物质,所产生的新分子或碎片往 往也有荧光特征,叠加在原有分子的荧光带上,使得所要检测的任何一种成份的荧光强 度对所有其它荧光猝灭物和敏化物的浓度及其荧光特征有很复杂的依赖关系,这就增加 了对实验所得到的荧光光谱解释的难度。     

乙醇醛的分子动态结构

以量子化学计算作为起点, 为最简单的糖类分子——乙醇醛开发了两套分子力学力场参数: 基于肽类的力场和基于醛类的力场. 分子动力学模拟结果表明, 所开发的类醛力场参数能够较好地描述乙醇醛分子在水中的结构以及水分子在其周围的分布. 通过瞬时简正模式分析, 得到了3N-6个模式的瞬时振动频率和振动跃迁偶极矩等振动光谱参数的统计分布及其相关性. 结合量子化学计算和分子动力学模拟对生物分子体系的多元振动光谱参数进行预测和评估, 为从化学键水平出发模拟宽带飞秒二维红外相关光谱提供了一个新方法.     

强红外激光场作用下固体甲酸铀酰的光解反应研究

关于在强红外激光场作用下多原子分子在气相介质中的多光子吸收(MPA)和解离(MPD)巳经进行过大量的研究.但是,在固相介质中这方面的研究尚属少见.迄今为止,只有Ambartzumyan等报道的TEA-CO_2激光使冻结在隔离基体上(isolated-matrix)的SF_6分子发生选择性的光解反应,以及Karlov等用类似的方法对BCl_3分子的光解反应研究.最近我们研究了一系列固体甲酸铀酰化合物的红外光谱,发现其中UO_2~(2+)基团的反对称振动频率v_a均在912—952cm~(-1)范围,与TEA-CO_2激光支线频率相符.本文研究TEA-CO_2激光作用下,单结晶水甲酸铀酰和碱式甲酸铀酰化合物发生光解反应的共同特性,并根据实验结果,初步提出了该光解反应的可能机理,即在强红外激光场下,这些化合物可以吸收多个光子而达到具有较高能量的振动激发态,在具有还原性的甲酸根离子作用下发生光解反应.     

丙酮酸分子结构与振动光谱的密度泛函理论研究

用密度泛函方法BLYP、B3LYP和从头算Hartree-Fock(HF)方法在6-31G*基组水平上对丙酮酸分子的几何结构（甲基的重叠式和交错式两种构象）和振动光谱分别进行了优化和计算,并给出了各种频率所对应的红外强度及拉曼活性,对光谱进行了指认。结果表明：在丙酮酸分子的两种构象中,重叠式比较稳定*B3LYP计算得到的构型参数与实验结果比较一致;在振动频率的计算中,BLYP未标度力场所计算的非CH3伸缩振动基频预测值和实验值的平均绝对偏差为10.4cm-1;而HF标度力场的平均绝对偏差为17.9cm-1。说明两者的结果与实验观测频率比较吻合,但B3LYP的频率计算值偏差（38.3cm-1）较大。根据振动频率的势能分布和红外光谱强度对此分子的振动基频进行了理论归属。     

甲醇团簇的多光子电离质谱及其从头算

用355 nm激光对脉冲分子束超声膨胀冷却的甲醇分子进行多光子电离, 飞行时间质谱仪观测到除甲醇碎片离子外的质子化甲醇团簇(CH3OH)nH+(n=1-16), 且离子的种类及相对强度与激光相对于脉冲分子束的延时无关, 取决于团簇离子内在结构的稳定性. 结合从头算密度泛函理论, 在B3LYP/6-31G(d)基组水平上优化得到了(CH3OH)n和(CH3OH)nH+(n=1-4)的稳定构型. 振动频谱分析显示, 团簇中最强的红外振动模主要来自氢键H伸缩振动的贡献. 团簇电离后发生于团簇内的质子转移反应也可能与激光电离引起的与氢键有关的振动模激发密切相关.     

OH-stretch vibrational relaxation of HOD in liquid to supercritical D2O

The population relaxation of the OH-stretching vibration of HOD diluted in D2O is studied by time-resolved infrared (IR) pump-probe spectroscopy for temperatures of up to 700 K in the density range 12 1 OH stretching transition with a 200 fs laser pulse centered at approximately 3500 cm(-1). Above 400 K these spectra show no indication of spectral diffusion after pump-probe delays of 0.3 ps. Over nearly the entire density range and for sufficiently high temperatures (T > 360 K), the vibrational relaxation rate constant, kr, is strictly proportional to the dielectric constant, epsilon, of water. Together with existing molecular dynamics simulations, this result suggests a simple linear dependence of kr on the number of hydrogen-bonded D2O molecules. It is shown that, for a given temperature, an isolated binary collision model is able to adequately describe the density dependence of vibrational energy relaxation even in hydrogen-bonded fluids. However, dynamic hydrogen bond breakage and formation is a source of spectral diffusion and affects the nature of the measured kr. For sufficiently high temperatures when spectral diffusion is much faster than energy transfer, the experimentally observed decays correspond to ensemble averaged population relaxation rates. In contrast, when spectral diffusion and vibrational relaxation occur on similar time scales, as is the case for ambient conditions, deviations from the linear kr(epsilon) relation occur because the long time decay of the v = 1 population is biased to slower relaxing HOD molecules that are only weakly connected to the hydrogen bond network.     

Formation Mechanism and Emission Spectrum of AlO Radicals in Reaction of Laser－ablated Al Atom and Oxygen

IntroductionLaser ablation has been applied broadly toplasma production,cluster formation,nanometermaterial and thin film material preparation[1,2 ] .Us-ing spectroscopic technique and mass spectrometryto identify the transient species formed in the pro-cess could provide much useful information aboutthe prosperity ofplasma,the mechanism of materi-al growth[3 ,4] .Aluminum is an important metal material andwidely used in industry and daily life. To study thereaction mechanism of Al atoms with…     

SF6在低温Ar基体中的红外光谱研究

Infrared spectra of SF_6 trapped in cryogenic matrix of argon have been measured. Five peaks are observed at the frequencies of 938.51, 938.05, 937.55, 939.82 and 936.22 cm~(-1) for the v_3 mode. Varying the concentration of SF_6 in argon matrix and diffusion studies indicate that the 937.55 cm~(-1) peak is due to SF_6 aggregate and the others arise from monomer. The changes in relative intensities with annealing show that there are at least three different trapping sites for monomeric SF_6 in argon lattice. The result that the increase in intensity of the peak at 938.03 cm~(-1) parallels the decrease in that of the peak at 938.51 cm~(-1) implies a temperature-induced-change in the site population.     

A matrix isolation study of 2-isopropylidenecyclopentane-1,3-diyl (Berson-type diradical)

The photodenitrogenation of diazene 5 in an argon matrix at 10 K permitted the first observation of an IR spectrum of 2-isopropylidenecyclopentane-1,3-diyl 2 (a Berson-type diradical). A comparison of the IR spectrum with a vibrational simulation at the B3LYP/6-31G(d) level of theory revealed that the diradical 2 has a planar structure. The oxygen-trapping reaction of 2 produced regioselectively fused peroxide 6 in an oxygen-doped argon matrix at 10 K. Irradiation of the diradical 2 afforded enyne 8 in an argon matrix at 10 K.     

Molecular structure, vibrational spectra and NBO analysis of phenylisothiocyanate by density functional method

The molecular geometry, vibrational frequencies and NBO analysis of phenylisothiocyanate (PITC) in the ground state have been calculated by using density functional theory calculation (B3LYP) with 6-311++G(d,p) basis set. The optimized geometrical parameters obtained by DFT calculations are in good agreement with experimental values. Comparison of the observed fundamental vibrational frequencies of the PITC and calculated result by density functional theory (B3LYP) indicates B3LYP is superior for molecular vibrational problems. The entropy of the title compound was also performed at HF/B3LYP/6-311++G(d,p) levels of theory. Natural bond orbital (NBO) analysis of title molecule is also carried out. A detailed interpretation of the IR and Raman spectra of PITC is reported on the basis of the calculated potential energy distribution (PED). The theoretical spectrogram for IR spectrum of the title molecule has been constructed.     

白花丹素分子结构和红外光谱的密度泛函理论研究

白花丹素(5-羟基-2-甲基-1,4-萘醌)是中药白花丹的主要成分之一,是一种具有抗肿瘤活性的萘醌类化合物.采用密度泛函(DFT)B3LYP/6-31+G(d)方法对白花丹素分子的几何构型进行全优化,得到其几何构型参数,进一步计算得到白花丹素的红外振动光谱.对计算得到的振动频率进行归属和解析并与文献值比较,发现理论计算...     

Relaxation of the individual vibrational levels of carbon monoxide following shock heating at 2100 K

The increases in the populations of the vibrational levels v = 1 to v = 5 in CO which is undergoing thermal vibrational relaxation at 2100 K have been monitored using a cw CO laser. The experiments have been carried out in a very narrow temperature range for mixtures of CO, Ar and He. Under these conditions the first part of the relaxation region is clearly visible, and it has been possible to compare the population growths of different vibrational levels under the same conditions. We have shown that the curve for the increase in the population of the level v = 1 with time is clearly different from those of the higher levels. It has been shown that all of the vibrational levels studied in this work on CO relax with a common vibrational temperature, as postulated in the model of Shuler and co-workers. The results reported here are qualitatively different from those presented by Chow and Greene on HI.     

Picosecond IR-UV pump-probe spectroscopic study of the dynamics of the vibrational relaxation of jet-cooled phenol. II. Intracluster vibrational energy redistribution of the OH stretching vibration of hydrogen-bonded clusters

A picosecond time-resolved IR-UV pump-probe spectroscopic study has been carried out for investigating the intracluster vibrational energy redistribution (IVR) and subsequent dissociation of hydrogen-bonded clusters of phenol (C6H5OH) and partially deuterated phenol (C6D5OH, phenol-d5) with various solvent molecules. The H-bonded OH stretching vibration was pumped by a picosecond IR pulse, and the transient S1-S0 UV spectra from the pumped level as well as the redistributed levels were observed with a picosecond UV laser. Two types of hydrogen-bonded clusters were investigated with respect to the effect of the H-bonding strength on the energy flow process: the first is of a strong "sigma-type H-bond" such as phenol-(dimethyl ether)(n=1) and phenol dimer, and the second is phenol-(ethylene)(n=1) having a weak "pi-type H-bond." It was found that the population of the IR-pumped OH level exhibits a single-exponential decay, whose rate increases with the H-bond strength. On the other hand, the transient UV spectrum due to the redistributed levels showed a different time evolutions at different monitoring UV frequency. From an analysis of the time profiles of the transient UV spectra, the following three-step scheme has been proposed for describing the energy flow starting from the IVR of the initially excited H-bonded OH stretching level to the dissociation of the H bond. (1) The intramolecular vibrational energy redistribution takes place within the phenolic site, preparing a hot phenol. (2) The energy flows from the hot phenol to the intermolecular vibrational modes of the cluster. (3) Finally, the hydrogen bond dissociates. Among the three steps, the rate constant of the first step was strongly dependent on the H-bond strength, while the rate constants of the other two steps were almost independent of the H-bond strength. For the dissociation of the hydrogen bond, the observed rate constants were compared with those calculated by the Rice, Ramsperger, Kassel, and Marcus model. The result suggests that dissociation of the hydrogen bond takes place much faster than complete energy randomization within the clusters.