摘要:
利用脉宽为5 ns脉冲Nd：YAG 355 nm激光在功率密度为10~（11）-10~（12）W/cm_2条件下实现了甲醛含水团簇多光子电离,并用飞行时间质谱对其电离产物和电离过程进行了研究.实验中观测到了甲醛的质子化团簇系列（CH_2O）,nH~＋（n=1-4）,甲醛的去质子化团簇系列（CH_2O）nCHO_＋n=1-3）,以及两个起源于H_2CO去质子和质子化的含水团簇系列HCO＋（H_2O）n（n=1,3,5）和H_3CO_＋（H_2O）n（n=1,3,5）,并对其中的一些团簇结构构型进行了猜测.研究在不同的激光功率密度下甲醛团簇质谱峰的变换情况,当激光密度达到9.3×10~（11）W/cm~2,开始出现CH_2O和H_2O本体及其光致碎片的信号,但对应的各质量峰没有明显地分辨开,而是以包络的形式出现,这是激光电离产生高能离子释放的一种表现,提出认等离子体动力学鞘层加速机制（模型）来解释高能离子形成的物理机制.
关键词:
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甲醛
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团簇
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飞行时间质谱
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激光电离
Abstract:
Multiphoton ionization of formaldehyde hydrated clusters is studied by time-of-flight mass spectrometry using 5 ns,355 nm Nd： YAG laser beam with a power intensity of 10~（11） -10~（12） W/cm~2.The main products including protonated formaldehyde cluster series （CH_20）_nH~＋（n = 1-4）,deprotonated formaldehyde clusters series（CH_20）_nCHO~＋（n = 1-3,and two series based on molecules originating from H_2CO（the deprotonated and protonated forms ）,H_3CO~＋（H_O）_nn = 1,3,5） and HCO~＋（H_2O）_n（n = 1,3,5） are observed,and the simple structures are gave for some clusters.The transformation of formaldehyde mass peak is studied in different laser power density conditions.We find the ion peaks of formaldehyde monomer and water molecle ar a laser intensity of about 9.3×10~（11） W/cm~2.Those mass peaks exist in envelope form and cannot be resolved under our experiment condition.The simple dynamic plasma sheath accelerating model is proposed to explain the physical mechanism of the envelope phenomenon.
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