纳秒激光电离分子团簇产生高离化离子的激光波长效应

 利用脉冲分子束-激光电离-飞行时间质谱仪，在10⁹～10¹² W·cm^-2激光功率密度条件下，考察了Nd：YAG激光器输出的1 064，532，266 nm波长的激光与苯、氨、硫化氢等团簇的相互作用。发现1 064 nm的激光可以电离分子束产生高离化态的C⁴⁺，N⁵⁺，S⁶⁺等离子；波长为532 nm的激光则电离产生价态较低的C³⁺，C²⁺，N³⁺，N²⁺， S⁴⁺，S³⁺以及S²⁺ 等离子；在266 nm波长条件下进行实验，没有产生任何高价离子。提出了一个“多光子电离引发-逆轫致吸收加热-电子碰撞电离”模型来解释高价离子的产生。激光场下电子在团簇内部的逆轫致加热是整个过程的关键步骤，电子被加热的速度正比于激光波长的平方。这可以解释为何长波长的激光有利于更高价态离子的产生。     

纳秒激光电离分子团簇产生高价离子实验研究

 利用飞行时间质谱仪，研究了功率密度为10⁹~10¹¹ W/cm²，波长为532 nm 的纳秒激光对苯、呋喃、甲醇及碘甲烷分子团簇的激光电离过程。实验观察到了高平动能的高价离子C^q+(q≤3)，O^q+(q≤3)和I^q+(q≤4)，该过程经历了以“初始的多光子电离引发-逆轫致吸收加热-电子碰撞电离模式”为主的激光团簇作用过程，后期经历了团簇的库仑爆炸过程。实验发现：即使激光能量变化一个量级以上时，主要高价离子的种类及占全部离子产物的比率也没有明显的变化，但是高价离子的初始平动能随激光强度的增大而增加；分子中含有较多个外壳层电子的氧、碘原子更容易电离产生高价离子，而碳离子的价态和强度相对较低。     

纳秒光场下原子团簇产生高离化Kr离子的激光波长效应

利用不同波长和光强的纳秒激光,对Kr原子团簇进行了激光电离的飞行时间质谱研究,观察到Kr高价离子价态显著地依赖于激光波长,当分别用波长为1064,532,355和266 nm的激光照射Kr原子团簇时,可分辨的离子最高价态分别为+17,+11,+4和+2价;然而离子价态与激光功率密度的依赖关系并不明显。实验结果支持多光子电离-逆轫致吸收加热-电子碰撞电离三步电离模型,表明电子碰撞电离是高价离子产生的主要途径。     

中等光强纳秒激光电离苯团簇产生多价碳离子的数值模拟和实验研究

飞秒强激光与团簇相互作用产生多价离子的现象已被广泛报道,然而近期多个研究小组发现当功率密度低至1010W/cm2的纳秒激光照射团簇时,同样也观察到了多价离子的存在.虽然可以用"多光子电离引发-逆韧致吸收加热-电子碰撞电离"电离机理对这种现象进行解释,但是缺乏相应的数值模拟.建立了一个简化的数值模型,根据有质动力势Up计算团簇内电子能量,再由Lotz公式计算出相应的电离截面,最后由动力学反应速率方程计算出团簇内多价碳离子随时间的演变.详细分析了团簇尺寸、电子密度等关键参数对多价离子产生的影响.数值模拟结果表明:团簇电离在小于0.7 ns时间尺度内完成,C2+,C3+和C4+多价离子强度达到平衡后,离子相对强度由大到小依次为C2+,C3+,C4+,这与实验结果相一致;多价离子的价态随着团簇尺寸的增加而升高,半径为5.6 nm的苯团簇比半径为3 nm的苯团簇更容易产生高价态的离子,这也与实验结果相一致.     

纳秒激光电离产生Kr17 + 的研究

随着激光技术 ,尤其是超快、超强激光技术的发展 ,强光场与原子、分子及团簇的相互作用 ,已成为近年来人们研究的热点[1 -8] .团簇分子与超快超强光场之间的相互作用 ,可以产生高价态离子以及高能电子 ,并产生强X射线发射甚至实现“台式核聚变” ,已引起广泛的重视 .Kr气及其团簇的强场电离 ,近年也有不少研究 .利用波长 1 .0 64μm的皮秒Nd YAG激光 ,Huillier等人在 1 0 1 3 ～ 1 0 1 4 W/cm2 光场强度下 ,研究了氪气的多光子电离过程 ,观察到 +4价的氪高价离子[7] .Castleman等人利用 80 0nm ,功率密度为 1 0 1 5W/cm2 的飞秒激光 ,对…     

甲基环己烷在9∽15.5 eV能量区的真空紫外光电离研究

利用具有同步辐射源的反射式飞行时间质谱仪，研究甲基环己烷的真空紫外光电离和光解离. 观测到母体离子C₇H₁₄⁺和碎片离子C₇H₁₃⁺，C₆H₁₁⁺，C₆H₁₀⁺，C₅H₁₀⁺，C₅H₉⁺，C₄H₈⁺，C₄H₇⁺和C₃H₅⁺的光电离效率曲线. 测定甲基环己烷的电离能为9.80±0.03 eV，通过光电离效率曲线确定其碎片离子的出现势. 在B3LYP/6-31G(d)水平上对过渡态、中间体和产物离子的优化结构进行表征，并使用G3B3方法计算其能量. 提出主要碎片离子的形成通道. 分子内氢迁移和碳开环是甲基环己烷裂解途径中最重要的过程.     

CS2团簇增强的激光多价电离现象的质谱研究

利用脉宽为25ns的脉冲Nd: YAG 532 nm的激光，在8×10¹⁰W/cm²的强度下，用飞行时间质谱对CS₂的激光电离过程进行了研究.观察到了较强的C²⁺和S²⁺高价离子信号，这些高价离子C²⁺，S²⁺的最可几平动能高达144 eV，112 eV.不同进样方式，激光延迟以及束源压力的实验结果表明，这些高价离子可能来源于CS₂团簇的库仑爆炸过程.多光子电离引发，逆韧致吸收加热-电子碰撞电离模型可能是高价离子产生的机理. 关键词： 2')" href="#">CS₂ 团簇 高价离子 激光电离     

甲醇/水混合团簇的多光子电离质谱研究

利用多光子电离技术结合飞行时间质谱仪对甲醇/水混合团簇进行了研究.在脉冲激光波长为355 nm条件下观测到团簇离子.主要的电离产物为质子化的(CH3OH)n(H2O)H+(n=l-13)混合团簇离子与(CH3OH)nH+团簇离子,经分析(CH3OH)1o(H2O) H+和(CH3OH)3H+为幻数结构.甲醇水混合团簇电离后团簇离子发生内部质子化转移反应是形成质子化团簇离子的主要原因.不同尺寸团簇离子信号强度随电离激光光强变化的光强指数曲线显示,团簇均发生四光子电离过程.     

苯和苯胺在深紫外光照射下的电离和解离

本文利用自主研制的反射式飞行时间质谱仪结合177.3 nm深紫外激光研究了苯和苯胺分子的光电离与光解离过程. 质谱实验发现苯在177.3 nm皮秒激光作用下发生高效电离并观测到不对称C-C键解离形成的以C₄H₃⁺为主的较小碎片峰. 相比之下，苯胺的深紫外光电离中主要产生一个C₅H₆^+·离子自由基和一个较小丰度的C₆H₆^+·碎片，分别对应于CNH分子和NH自由基的去除. 结合第一性原理计算，诠释了苯和苯胺这两个仅有一个氨基差异的分子光解离路径，揭示苯和苯胺分子中氢原子转移对于C-C或C-N键断裂的关键重要作用.     

纳秒强激光中丙酮团簇增强的多价电离现象

利用脉宽为25 ns的脉冲Nd: YAG 532 nm的激光，在10¹⁰—10¹¹ W/cm²的强度下，用飞行时间质谱对丙酮团簇的激光电离过程进行了研究. 观察到了较强的O^q+(q=2—4)和C^q+(q=1—4)高价离子信号，这些高价离子 C⁴⁺，C³⁺，C²⁺，O⁴⁺，O³⁺，O²⁺的最大概然平动能分别为240 eV，70 eV，30 eV，90 eV，80 eV，40 eV. 高价离子的强度和平动能随激光强度的增大而增大. 我们提出一个多光子电离引发，逆韧致吸收加热-电子碰撞电离模型来解释高价离子的产生. 关键词： 丙酮 团簇 库仑爆炸 高价离子     

Ellipticity-dependent of multiple ionisation methyl iodide cluster using 532 nm nanosecond laser

The dependence of multiply charged ions on laser ellipticity in methyl iodide clusters with 532 nm nanosecond laser was measured using a time-of-flight mass spectrometer. The intensities of multiply charged ions I^q+(q = 2–4) with circularly polarised laser pulse were clearly higher than those with linearly polarised laser pulse but the intensity of single charged ions I⁺ was inverse. And the dependences of ions on the optical polarisation state were investigated and a flower petal and square distribution for single charged ions (I⁺, C⁺) and multiply charged ions (I²⁺, I³⁺, I⁴⁺, C²⁺) were observed, respectively. A theoretical calculation was also proposed to simulate the distributions of ions and theoretical results fitted well with the experimental ones. It indicated that the high multiphoton ionisation probability in the initial stage would result in the disintegration of big clusters into small ones and suppress the production of multiply charged ions.     

乙醚团簇在纳秒激光场中的多价电离及其电子能量分布的研究

用5ns,1064nm的脉冲Nd:YAG激光,研究了乙醚团簇与纳秒激光的相互作用.在10¹¹ W/cm²量级光强下,观察到价电子完全剥离的O⁶⁺,C⁴⁺,且这些高价离子的强度比值基本不随激光能量而变化.用阻滞电压方法测量了电离过程中溢出电子能量分布,在最大激光能量4.0×10¹¹ W/cm²,溢出电子的平均能量为56eV,最大能量为102eV.实验结果支持了高价离子产生的“多 关键词： 高价离子 电子能量 纳秒激光 乙醚团簇     

Cluster-assisted generation of multiply charged ions in nanosecond laser ionization of seeded furan beam at 532 and 1064 nm

The multiply charged ions of C ^{q +} (q ≤ 4), O ^{q +} (q ≤ 6) were produced when a furan cluster beam interacted with nanosecond 1064 and 532 nm lasers at intensities of 10¹⁰–10¹² W/cm². It is shown that O⁶⁺ and C⁴⁺ ions were the dominant multiply charged species at 1064 nm, while C²⁺, C³⁺, O²⁺, O³⁺ ions were the main multiply charged species at 532 nm. By varying the electric field in the extraction region of the time of flight mass spectrometer (TOFMS), two types of ions were extracted, one of which had large kinetic energy and narrow space distribution, and the other had small kinetic energy and broad space distribution. The formation channels for He-like ions of C⁴⁺ and O⁶⁺ are discussed.     

Kinetic energy distributions of the fragment ions from multiply ionized C2H6 as functions of the charge state of the intermediate states

Here, we report the kinetic energy distributions (KEDs) of the fragment ions produced from multiply ionized ethane (C₂H₆) molecules in single electron capture collisions with 1.2 MeV C²⁺. To systematically investigate the fragmentation dynamics, the KEDs were obtained as functions of the charge state of the intermediate C₂H₆^r+* ions r transiently generated prior to fragmentation. r was determined from coincidence measurement of the fragment ions and the number of emitted electrons. The KEDs are drastically different depending on the number of broken C–H bonds. The underlying causes are explained by the variation of the relative contributions of the multiply ionized states and preferential fragmentation pathways. For instance, CH_n⁺ fragment ions with smaller n exhibit lower KEs because they are likely to be correlated with H⁺ emission, which carries away a large portion of the KE release. In addition, we report the KEDs of H₃⁺ produced from doubly and triply charged states.     

Thermonuclear fusion in the irradiation of large clusters of deuterium iodide with a field of a superatomic femtosecond laser pulse

A theory of thermonuclear fusion caused by the irradiation of deuterium-iodide clusters with the field of a superatomic femtosecond laser pulse is developed. It is based on considering the process in which the sequential above-barrier multiple internal ionization of atomic ions within a cluster is accompanied by external field ionization. The theory is illustrated by taking the example of a cluster that is formed by 10⁶ molecules of deuterium iodide and which is irradiated with a laser pulse of duration 50 fs and intensity 2×10¹⁸ W/cm² at the peak. This case is dominated by I²⁶⁺ atomic ions. The yield of neutrons from thermonuclear fusion in a deuteron-deuteron collision upon the passage of a laser pulse is calculated. The result is 10⁵ neutrons per laser pulse. The mean kinetic energy of deuterons is estimated at 50 keV. Owing to induced inverse bremsstrahlung in scattering on multiply charged atomic ions, the electron temperature increases up to 28 keV. The role of the Mie resonance in the heating of the electron component is discussed.     

Many-body effects in the formation of multiply charged ions in a strong laser field

Some of the many-body effects in the formation of multiply charged ions in a laser field have been taken into account: inelastic tunneling, collective tunneling, and magnetic moment projection relaxation of the atomic core. Strong fields with an intensity exceeding 10¹⁷ W cm⁻² are considered when the magnetic component of the laser field acts on the free motion of a photoelectron; therefore, the formation of multiply charged ions through rescattering becomes unlikely. Numerical calculations have been performed for Ar⁹⁺ … Ar¹³⁺, Kr¹⁹⁺ … Kr²³⁺, Rb¹⁰⁺, and Rb¹¹⁺ ions. A significant contribution of collective tunneling, which was not observed in weaker fields investigated previously, has been revealed. Allowance for collective tunneling is shown to reduce the intensity leading to saturation by more than 10%. In this case, the yield of multiply charged Rb ions changes by an order of magnitude, while the yield of multiply charged Ar and Kr ions changes by more than a factor of 2. Comparison with experimental data on the formation of argon ions under the action of a linearly polarized laser pulse is made.