532nm纳秒激光电离分子团簇产生高价离子实验研究

Multiple ionization of carbonaceous molecule clusters by intense 532 nm nanosecond laser

利用飞行时间质谱仪,研究了功率密度为109～1011 W/cm^2,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Cq＋（q≤3）,Oq＋（q≤3）和Iq＋（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.

Using time-of-flight mass spectrometry, the multiple ionization process of seeded molecular cluster beams was studied by 532 nm nanosecond laser with intensity from 10^10 to 10^11 W · cm^-2. Ions of C^q＋ , O^q＋ and I^1＋ （q=2-4） with translational energy of hundreds of eV were observed when the densest portion of the pulsed molecular beams of benzene, furan, methanol and methyl iodide were irradiated by the nanosecond laser. A model of ＂multiphoton ionization ignition-inverse bremsstrahlung absorption heated-electron collision ionization＂ is proposed to explain the generation of those multiply charged ions under the low intensity laser pulse. The kinds of the multiply charged ions as well as the ratio of each ion to the overall ion products did not decrease apparently even if the laser intensity decrease to 1/25 of the highest intensity. It is easier to ionize for the molecules containing the atoms with more valence electrons, such as oxygen atom and iodine atom, while the charge and product of the carbon ions are lower.