【作者】 汪华；

【导师】 刘世林；

【作者基本信息】 中国科学技术大学 ， 化学物理， 2007， 博士

【摘要】 本论文的研究工作包括两部分：(一)N2O+离子A2∑+电子态转动光谱和光解动力学研究,(二)HNCO分子210nm处的光解动力学研究。N20+离子A2∑+电子态转动光谱和光解动力学研究用一束波长为360.55nm的激光,通过N20分子的(3+1)]REMPI过程制备纯净的母体离子N2O+X2Π3/2,1/2(000),用另一束波长为280-320nm的激光将制备的母体离子N2O+激发至预解离态A2∑+,探测解离碎片NO+离子强度随解离激光波长的变化,首次获得了N2O+离子A2∑+电子态高振动能级的转动光谱结构。通过对光谱转动结构的拟合,得到了N2O+离子A2∑+电子态一系列高振动能级的转动常数和自旋分裂常数。利用离子速度成像技术,研究N2O+离子A2∑+电子态光解动力学。得到A2∑+电子态一系列高振动能级解离产物NO+的速度分布和角分布。实验结果表明,碎片NO+的角分布呈现各向同性,为明显的预解离结果；首次观察到解离碎片NO+的速度分布由三部分组成。结合A2∑+电子态势能面信息,我们对N2O+离子A2∑+电子态的预解离机理进行了探讨,认为在碎片NO+分别来源于NO++N(4S)通道的解离,以及NO++N(2D)通道产生的高转动NO+和低转动NO+。由于来源于N(2D)解离通道的产物经历了两种路径,导致了碎片NO+的转动激发有所不同。HNCO分子210nm处的光解动力学研究用一束波长为210nm的激光,将HNCO分子由基态S0泵浦到激发态S1,然后发生解离,用另一束波长为230nm激光通过共振多光子电离(REMPI)经由CO(B1Σ+←←X1Σ+)跃迁来探测解离产物,采用速度切片成像技术得到了产物CO(v=0,J=35和J=30)速度分布图像,进而得到解离时碎片的总平动能分布及角分布。结果表明：HNCO分子210nm处的光解主要通道是产生NH(a1Δ)+CO(X1Σ+)的通道；碎片CO具有很高的转动激发,而NH的转动激发很小,约50%可资用能转化为平(?)能,该通道解离能确定为42738cm-1；解离各向异性参数β最小为-0.75,且随着NH激发增大。该研究首次实验上证实了HNCO分子的快速、直接解离过程。β值随NH的转动变化可以用经典碰撞模型予以解释。更多还原

【Abstract】 This dissertation presents the experimental studies on the following two aspects: (1)Rotational Spectrum and Photodissociation Dynamics of N2O+(A2E+). (2)Photodissociation Dynamics of HNCO molecules at 210nm.Rotational Spectrum and Photodissociation Dynamics of N2O+(A2Σ+)The rotational structures of the photo fragment excitation spectrum of N2O+(A2E+) at high vibrational levels have been studied experimentally. The parent N2O+(X2Π) ions were prepared by [3+1] resonance-enhanced multiphoton ionization of jet-cooled N2O molecules at 360.55nm, and were excited by another laser to the predissociative A2E+state in the range of 280-320nm. Two types of rotational transition, i.e., 2Σ+←2Πand 2Π←2Π, have been clearly observed for a series of vibronic transitions for the first time. The rotational constants and spin splitting constants have been obtained from the spectral analysis.The photofragment NO+velocity imagings have been studied at high vibrational levels of N2O+(A2E+). And both angular and translational energy distribution have been obtained by integrating the imagings. It indicate the predissociation process on N2O+(A2Σ+) with the isotropy of NO+angular distribution. And it is found that there are three compositions in the total translational energy distribution. The conclusion is made that NO+fragments come from the NO++N(4S) and NO++N(2D) channels, However, the produce NO+from N(2D) channel pass through two pathways, and induce high and low rotational excitation.Photodissociation Dynamics of HNCO molecules at 210nmThe photodissociation of isocyanic acid (HNCO) on the first excited singlet state (S1) following the excitation at 210 nm has been investigated with ion velocity slice imaging technique by probing the CO fragment. It was found from the (2+1) resonance-enhanced multi-photon ionization (REMPI) spectrum that the CO fragment is rotationally hot with population up to Jmax=50. The velocity imagings of CO fragment at Jco=30 and 35 indicate that formation of NH(a1Δ)+CO(X1Σ+,v=0) is the predominant dissociation channel at 210nm. From analysis of the CO fragment translational energy distributions, the NH(a1Δ) fragment was observed to be rotationally cold, about half of the available energy was partitioned into the translational motion of fragments after dissociation, and the NH(a1Δ)+CO(X’Σ+) dissociation threshold was determined at 42738±30cm-1. From analysis of the CO fragment angular distributions, the dissociation anisotropy parametersβwere found to be negative, and increase with the rotational quantum number of NH fragment, i.e., from-0.75 at JNH=2～4 to -0.17 at JNH=11. Impulsive direct and vertical dissociation process of HNCO on the S1 state at 210nm was confirmed. A classical impact dissociation model was employed to explain the dependence ofβvalue on the rotational levels of NH fragment.更多还原