氩原子共振增强多光子电离谱--奇对称性里德堡态

利用脉冲放电产生氩原子亚稳态4s2[3/2]°2和4s′2[1/2]°0,在610～670nm波长范围内,利用共振增强多光子电离和飞行时间质谱技术得到氩原子(2+1)REMPI谱.光谱分析表明所有谱线来源于氩原子4s2[3/2]2和4s′2[1/2]°0两个亚稳态向16个奇对称性里德堡态双光子跃迁,并标识所有谱线.同时首次在实验上观察到一个长序列的3p54s′2[1/2]°0→3p5nd2[1/2]°1(n=8～31)双光子跃迁.在实验技术上,提供了一种研究惰性气体原予以及其它原子高里德堡态和自电离态的新方法.     

三氯乙烯分子的多光子电离解离研究

用可调谐染料激光器 ,在 4 5 0— 4 75 nm范围内 ,在飞行时间质谱仪上研究了三氯乙烯分子的共振增强多光子电离解离过程。研究表明 ,在此实验波段内三氯乙烯分子经历了从 π到 3d里德堡态的 (3 1 )多光子过程 ,可以用母体离子阶梯开关模型对三氯乙烯的电离解离过程进行解释 ,并对振动能级进行了标识 ,对振动频率进行了计算     

430-490nm激光作用下CH_3I分子的多光子电离离解研究

利用飞行时间质谱仪研究了CH3I分子在 4 30～ 4 90nm激光作用下的多光子电离 (MPI)离解过程和机制。得到了分子的飞行时间质谱 ,从整个实验波段 4 30～ 4 90nm的MPI离子谱发现 ,短波的MPI离子谱峰相对较高 ,长波的MPI离子谱峰相对较宽而弥散。对MPI离子谱中的一些共振峰标识为分子的 ( 5pπ ,8s) ,( 5pπ ,6p)以及 ( 5pπ ,7s)里德堡态共振吸收峰。还标识了 ( 5pπ ,7s)里德堡态的系列振动模。在短波段CH3I分子为 ( 3+1)多光子过程 ,长波段为 ( 2+2 )多光过程。     

6-甲基吲哚的共振多光子电离光谱分析

获得了6-甲基吲哚的单色共振多光子电离和双色共振多光子电离光谱,发现了在电子激发态的较强的CH3的转动谱线.根据理论计算对观察到的激发态光谱进行了标识,确定了更准确的电离能为60967±5cm-1.     

气相吡啶分子S1态的(2+3)偏振共振多光子电离谱研究

利用气相吡啶分子分别在圆偏振光激发和线偏振光激发下的（２＋３）偏振共振多光子电离（ＰＲＭＰＩ）谱,对其第一激发态（Ｓ１）上的振转结构进行了研究。在谱中观察到了呈双峰结构的电子振转跃迁谱带。分析表明,所有振动谱带均为Ｓ１态上Ｖ６ａ、Ｖ１０ａ、Ｖ１２、Ｖ１６ｂ和Ｖ１７ａ以及基态上Ｖ９ａ的混合频率谱带。旨认吡啶Ｖ１７ａ的Ｓ１态频率为６７０ｃｍ＾－１,并认为在Ｓ１态上Ｖ７ａ频率降低的原因与Ｖ１０ａ类似。     

NO(3+1)共振增强的多光子离化谱

用皮秒脉冲高功率Nd∶YAG激光器抽运的光学参量发生/放大器作激发源,获得了NO分子在420～500 nm波长范围内的多光子离化谱,光谱图呈现分离谱的特征,表明在该波长区间NO分子以多光子共振方式离化。离化信号随激光强度的近四次方变化关系表明,在420～500 nm波长范围内NO分子吸收4个光子而离化。通过对谱线的标识,首次分离出NO分子以E 2Σ激发电子态为中间共振态的(3+1)多光子离化光谱序列,由谱线序列峰值波长得到NO分子E 2Σ电子态的振动常数,从而实现了采用多光子离化技术对该态能级结构的实验研究。     

243—263nm S原子Rydberg态的(2+1)共振增强多光子电离

在243—263nm波长范围,测量了S⁺分质量激发谱,得到SO₂分子光解产生的S原子近50条(2+1)共振增强多光子电离谱线．除了来自S原子基态3p⁴³P_2,1,0直至n=10的Rydberg态³P,³D,³F的许多双光子跃迁谱线外,观察到若干新的¹P⁰,⁵S^关键词：     

激光光解NO2产物NO(X2∏)的REMPI离子谱的标识与研究

利用Nd:YAG激光器三倍频、输出波长为＝ 355 nm的激光光解NO2分子,可产生NO分子,将NO分子通过共振增强多光子电离(REMPI resonance enhanced multiphoto ionization)及飞行时间(TOF time of flight)质谱技术,获得振转态分辨的NO( X2∏,υ″J″)离子谱NOγ(0,0),γ(0,1),γ(1,1).通过理论计算 , 可将NO离子带的P、R、Q支线进行标识.NO分子的离子信号强度与UV电离激光能量(λ≈226 nm)之间关系能用二次方曲线很好拟合.它表明NO分子是通过(1+1)双光子吸收而电离.这些结果对NO分子的电离动力学提供了有益的信息.     

丙酮分子的分质量共振多光子电离光谱及多光子电离—离解机理研究

用多光子电离飞行时间质谱法三光子与丙酮分子３ｄ形态和４ｓ态共振的激光波长区域获得了丙酮分子的共振多光子电离分质量多光子电离（ＭＰＩ）光谱和飞行时间质谱，实验观察到的主要产物是ＣＨ３ＣＯ＾＋和ＣＨ＾＋３，还观察到了少量的Ｃ＾＋，ＣＨ＾＋，ＣＨ＾＋２和ＣＨＯ＾＋，在实验的激光波长范围内未见到母体离子，分质量多光子电离光谱具有相似的光谱结构，几个主要谐峰分别对应着（ｎ０，３ｄ）和（ｎ０，４ｓ）里德堡跃迁     

激光光解NO2产物—NO分子NO（X2П）与氧原子O(3PJ″)的REMPI离子谱研究

利用激光光解NO₂分子,通过共振增强多光子电离(REMPI resonance enhanced multiphoto ionization)及飞行时间（TOF time of flight）质谱技术,获得了振转态分辨的NO（Ｘ^２Π,υ″,Ｊ″）与自旋-轨道分辨的氧原子O（２Ｐ^３Ｐ_{Ｊ″＝２,１,０})离子谱.NO分子与O原子的离子信号强度与ＵＶ电离激光能量之间的关系分别能用二次方和三次方曲线很好拟合,它表明:光解产物NO分子和氧原子是分别通过（1+1）和（2+1）多光子吸收过程而被电离的.由氧离子信号得到的氧原子基态三个自旋-轨道支能级布居比f_１与f_０分别为0.54±0.09和 0.20±0.04,这一比值与统计分布计算的值为0.6和0.2一致.     

Scattering of N2 from Ni(111)

A cold (T_rot<10 K) beam of N₂ with an initial translational energy of 0.40 eV strikes an Ni(111) surface at surface temperatures from 300 to 873 K at several incident angles from 15 to 60°. The rotational energy and angular distributions of the scattered molecules are probed using (2+1) resonance-enhanced multiphoton ionization. Molecules scattered in the specular direction have mean rotational energies that are independent of surface temperature, whereas those scattered at angles far from the specular show a dependence on surface temperature, caused likely by multiple collisions with the surface before escape. A rotational rainbow, seen in systems such as CO–Ni(111) and N₂–Ag(111), is not seen in this system. For molecules that scatter close to the specular direction, approximately 10% of the initial translational energy is converted into rotational energy of the scattered N₂. For surface temperatures above room temperature, the angular distributions indicate that molecules that scatter into low-J states also tend to exit in a broad peak (10–20° FWHM) near the specular, and this peak is broadened with increasing incident angle. The molecules that scatter into high-J states have a much broader distribution, indicating that they are trapped rotationally during the initial collision and suffer multiple collisions before leaving the surface.     

On the ultraviolet absorption of nitrous oxide and its van der Waals complexes

The possibility of simultaneous characterization of N₂O and N₂O van der Waals complexes in supersonic jet expansions is demonstrated for neat N₂O samples. Room temperature and jet-cooled spectra of the Rydberg transitions 3pπ¹Δ ←← X¹Σ⁺ and 3pσ¹Π ←← X¹Σ⁺ are presented. Theoretical calculations support the assignment of the Rydberg transitions used. For stagnation pressures above 2 bar, a hitherto unreported broad spectral feature at 84 650 cm⁻¹ is observed, where calculations predict absorption of the (N₂O)₂ dimer essentially due to excitation of the 4sσ and 3pπ Rydberg orbitals. Consequences for the use of N₂O as a precursor for O(¹D) atoms in reactive scattering experiments are discussed.     

Translational energy release in the recombinative desorption of H2 from Ag(111)

We have investigated the recombinative desorption of H₂ from Ag(111) using (2 + 1) REMPI to detect the desorbing molecules. We describe a method for determining the energy released into translational motion normal to the surface over a wide range of surface temperatures. This was achieved by using a weak electric field to disperse the ions, in contrast to the usual field-free method. Calibration and analysis methods are discussed and energy distributions P(E) are reported for H₂ (v=0). Desorption from a 295 K surface shows only a single low-energy peak ( ), whereas the translational energy release is bimodal for desorption from a 580 K surface, with mean desorption energies of approximately 140 meV and 1 eV for the two pathways. Sticking functions are calculated using detailed balance, revealing a large dependence on surface temperature.     

Electron stimulated desorption of CO molecules from chemisorbed CO layers on Ru(001): a comparison of the distributions of translational and internal energies

The translational and internal energies of CO desorbed by electron impact from well-ordered × layers on Ru(001) are investigated with time-of-flight techniques and resonance enhanced multiphoton ionization (REMPI) spectroscopy. We discriminate four desorption channels with different translational and internal energy distributions. Translational and vibrational energies are positively, crrelated; rotational and vibrational–translational energies are negatively correlated. The microscopic origins of these correlations are discussed.     

Photoinduced processes on alkali covered surfaces: NO desorption from K/Cr2O3(0001)

We have studied the ultraviolet laser induced desorption of NO/Cr₂O₃(0001), K/Cr₂O₃(0001) and the coadsorbate system NO/K/Cr₂O₃(0001) using resonance enhanced multiphoton ionization spectroscopy for state selective detection of the desorbing species after excitation with nanosecond laser pulses. The goal of our experiments was to study the influence of surface electronic modifications via alkali adsorption on the photodynamics of a simple molecule. The photochemistry of the isolated and the coadsorbate systems is strongly dependent on the coverage of the diverse components. In this paper we shall mainly focus on data for the low coverage regime of potassium. From the two adsorbate species of NO, a chemisorbed and a physisorbed species, we present data of the chemisorbed species. The velocity distributions show a strong dependence on the excitation energy which we interpret on the basis of electron energy loss spectra as being due to surface charge transfer states. This is corroborated with our coadsorption experiments with low coverages of potassium which alter the velocity distributions.     

氦原子1snd(n=4—11)组态下1D—3D谱项分裂值的计算

利用多体微扰理论(MBPT)计算了氦原子1snd(n=4—11)组态的１Ｄ—^３Ｄ谱项分裂值.基于两种不同的模型分别计算Rayleigh-Shrdinger微扰展开式中仅含束缚态的部分和包含连续态的部分.对于束缚态，较严格地通过自洽迭代求解Hartree方程构造零级近似波函数，并利用积分处理方法对无穷项求和中的余项给出了近似算法.而对于连续态波函数，则采用简化的氢原子势模型.按照Rayleigh-Shrdinger微扰展开方法，将Rydberg态的微扰论修正计算至三级.计算表明，二级和三级微扰对谱项分裂的贡献主要来自于束缚态求和部分.单态-三重态精细结构分裂的计算结果与两组实验结果基本符合. 关键词： 氦原子 Rydberg态 多体微扰 组态波函数 能级分裂     

A REMPI study of the correlation of internal excitations and substrate-adsorbate coupling for CO molecules desorbed by electron impact

We compare vibrational, translational and rotational excitations of CO molecules desorbed by electron impact, and the yield of oxygen and carbon atoms from electron-induced fragmentation of CO molecules for: (1) CO monolayers on bare transition metals [Ru(001) and Pt(111)]; (2) CO monolayers coadsorbed with well-ordered oxygen atoms; (3) weakly bound CO monolayers on epitaxially grown silver films; and (4) CO monolayers decoupled from the metallic substrate by mono-atomic xenon spacer layers. For all but the last system, we find CO molecules which are vibrationally extremely hot. This is explained by the excitation of strongly antibonding multi-electron states which are quenched in the vicinity of the metal surface before enough translational energy is acquired by the nuclei to complete dissociation. For CO/Xe/Ag(111), vibrationally hot CO molecules are missing among the desorbing particles, whereas strong fragment signals persist. Because of the isolating Xe layer, the substrate-adsorbate coupling is too weak to terminate the dissociation reaction which is induced by the electron impact before the rupture of the molecular bond.