激光偏振特性对丙酮和氧气多光子电离质谱信号的影响

在极性分子丙酮复合物CH3COCH3*H2O和非极性分子氧气的REMPI谱中,母体离子信号强度与激光偏振方向的关系是不同的.改变532 nm激光偏振方向,记录了两种分子母体离子信号强度,实验结果表明,对于氧气分子的母体离子信号强度,激光偏振方向的改变对其没有影响,而对于CH3COCH3*H2O的母体离子信号强度,随偶极矩与激光偏振方向夹角的增加,其母体离子信号强度呈余弦曲线变化,且与夹角余弦的2.1次幂成正比.理论分析显示,CH3COCH3*H2O的REMPI母体离子信号强度应与此夹角的余弦的2次幂成正比.这就说明实验结果和理论分析是相符的.     

MULTIPHOTON IONIZATION MASS SPECTRA OF n-C3H7I AND i-C3H7I AT 532 nm

Multiphoton Ionization (MP) Mass Spectra of n-C₃H₇I AND i-C₃H₇I are obtained using a time-offlight mass spectrometer at 532 nm. No parentions are observed in MPI of both isomers. N-propyl cation dissociates more extensively than isopropyl cation. The C₂H⁺₅(M/Z=29) ion is observed instead of C₂H⁺₄(M/Z=28) ion in MPI of n-C₃H₇I, in contrast to i-C₃H₇I. It is found that parent molecules are first two-photon resonantly excited to A-band, then go through dissociation. Fragment ions are produced by ionization and dissociation of neutral fragments. We present directly the diss ociation pathways of n-propyl cation according to the results proposed by Levine using maximum entropy formalism. Moreover, those of isopropyl cation are discussed in this paper through branching ratio analyses.     

CH3I分子在440—510nm激光作用下多光子电离

利用飞行时间质谱仪研究了CH₃I分子在440—510nm波段的多光子电离(MPI)机理.在该波段，CH₃I分子吸收三光子激光能量与(5pπ,6p)里德伯态高频端发生共振，然后继续吸收光子电离解离成最终产物离子. 关键词：     

纳秒强光场下碘甲烷的激光电离中高价离子产生研究

利用25纳秒脉冲Nd-YAG 532 nm的激光,在1011 W cm-2的光场强度下,用飞行时间质谱对不同载气条件下碘甲烷的激光电离过程进行了研究.当利用氩作为载气时,除观察到H+,C+,CH+,CH+3,I+,CH3I+等离子外,还观察到很强的C2+,I2+和I3+离子信号.这些高价离子的最可几平动能分别为55.5 eV,9.5 eV和27 eV.质谱峰形的分裂现象以及不同载气的实验结果表明这些高价离子可能来源于碘甲烷团簇的库仑爆炸过程.     

N II离子禁戒跃迁几率的理论计算

用多组态Dirac-Fock方法, 系统考虑了相对论效应、电子关联、延迟效应等重要贡献, 计算了N II离子2p3d-2p2以及2p3d-2p3p (ΔL＝±2, ΔS＝±1)禁戒跃迁的几率. 与已有的理论相比, 目前计算的精度有了明显提高.     

355 nm激光作用下质子化丙酮-水团簇的多光子电离质谱

为研究由氢键形成的超分子体系内的质子化构型,利用355 nm多光子电离(MPI)技术结合飞行时间质谱（TOF-MS）得到丙酮和水的系列团簇质谱.实验观察到的主要产物是质子化的丙酮水团簇.其团簇构型归纳为(CH3COCH3)n(H2O)n－2H+,(CH3COCH3)n(H2O)n－1H+和(CH3COCH3)n(H2O)nH+.利用Gaussian 98程序优化了团簇的离子态构型,通过频率验证了构型的稳定性,并给出了相关能量和零点修正能.     

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.     

激光溅射Cu等离子体与气相C2H5OH团簇的反应

用激光溅射-分子束技术研究了气相中Cu的等离子体与乙醇分子团簇的反应.观察到三种团簇正离子Cu＋(C2H5OH)n、CuO＋(C2H5OH)n、H＋(C2H5OH)n和三种团簇负离子(C2H5OH)nC2H5O－、(C2H5OH)n(H2O)OH－、(C2H5OH)n(H2O)2OH－(n≤12).详细考察了在不同的载气压力下激光烧蚀等离子体作用于脉冲分子束， 以及在一定的压力下等离子体作用于分子束不同位置时，对团簇产物种类和团簇尺寸大小的影响.分析了Cu＋(C2H5OH)n、CuO＋(C2H5OH)n、H＋(C2H5OH)n、(C2H5OH)nC2H5O－、(C2H5OH)n(H2O)OH－、(C2H5OH)n(H2O)2OH－等团簇的产生机理.     

266 nm激光作用下对溴甲苯多光子电离质谱的研究

利用266 nm激光作为光源研究了对溴甲苯分子的多光子电离解离,得到了对溴甲苯的多光子电离飞行时间质谱.实验测得了部分碎片离子占总离子信号的分支比对激光强度的依赖关系,分析了对溴甲苯分子的多光子电离解离机理,讨论了C4H+7,C6H+,C5H+5等碎片离子的可能形成过程.结果表明,碎片离子主要是经过离子离解阶梯模式产生.对实验中观测到的由激光强度变化引起的质谱峰值漂移现象作了说明.     

One-colour resonant two-photon ionization spectrum of the 1-fluoronaphthalene dimer and ab initio calculation

The one-colour resonant two-photon ionization(R2PI) spectrum of the 1-fluoronaphthalene(1FN) dimer has been studied in the wavelength range of 304 to 322 nm by using a supersonic molecular beam and time-of-flight mass spectrometry.Compared with the original band 00(at 313.8 nm) of the S1 ← S0 transition of the 1FN monomer,a red-shifted band was observed in the 1FN dimer spectrum at about 315 nm with a relatively large linewidth,nearly 2 nm.Based on the consideration of inductive effect and ab initio calculations,this red-shifted band is assigned to the first electronic excited transition of the 1FN dimer.A possible geometric structure of the 1FN dimer is also obtained with calculations that the two 1FN molecules are combined through two hydrogen bonds which are formed between the hydrogen atom of a molecule and the fluorine atom of a neighbouring molecule.A time-dependent calculation was also carried out and the results are consistent with the experimental data.