强飞秒激光场下二氧化碳二聚体四价离子的多体解离动力学

Dynamics of many-body fragmentation of carbon dioxide dimer tetravalent ions produced by intense femtosecond laser fields

开展了强飞秒激光场诱导的二氧化碳二聚体离子(CO_(2))_(2)^(4+)的三体库仑爆炸过程的实验研究.利用冷靶反冲离子动量成像谱仪测量了关联的碎片离子的三维动量矢量和动能.结果表明,(CO_(2))_(2)^(4+)离子通过序列解离通道和非序列解离通道分解为CO_(2)^(2+)+C+CO^(+)+O^(+)离子.在序列解离过程中,弱范德瓦耳斯键先断裂,然后是强的共价键C=O断裂;而在非序列解离过程中,3个碎片离子在一次动力学事件内几乎同时产生.通过对比两个解离通道的事件比率,表明序列的解离通道在(CO_(2))_(2)^(4+)离子的三体库仑爆炸中占主导作用.发现这种同时包含范德瓦耳斯键和共价键的二聚体或团簇在多体库仑爆炸过程中相比单体和仅有范德瓦耳斯键的团簇具有特殊的动力学性质,两种化学键在强场动力学过程中扮演不同的角色.

We study experimentally the three-body Coulomb explosion dynamics of carbon dioxide dimer(CO_(2))_(2)^(4+)ions produced by intense femtosecond laser field.The three-dimensional momentum vectors as well as kinetic energy are measured for the correlated fragmental ions in a cold-target recoil-ion momentum spectrometer(COLTRIMS).Carbon dioxide dimer is produced during the supersonic expansion of(CO_(2))_(2)gas from a 30μm nozzle with 10 bar backing pressure.The linearly polarized laser pulses with a pulse duration(full width at half maximum of the peak intensity)of 25 fs,a central wavelength of 790 nm,a repetition rate of 10 kHz,and peak laser intensities on the order of 8×10^(14)W/cm^(2)are produced by a femtosecond Ti:sapphire multipass amplification system.We concentrate on the three-particle breakup channel(CO_(2))_(2)^(4+)→CO_(2)^(2+)+CO^(+)+O^(+).The two-particle breakup channels,(CO_(2))_(2)^(4+)→CO_(2)^(2+)+CO_(2)2+and CO_(2)^(2+)→CO^(+)+O^(+),are selected as well for reference.The fragmental ions are guided by a homogenous electric field of 60 V/cm toward microchannel plates position-sensitive detector.The time of flight(TOF)and position of the fragmental ions are recorded to reconstruct their three-dimensional momenta.By designing some constraints to filter the experimental data,we select the data from different dissociative channels.The results demonstrate that the three-body Coulomb explosion of(CO_(2))_(2)^(4+)ions break into CO_(2)^(2+)+CO^(+)+O^(+)through two mechanisms:sequential fragmentation and non-sequential fragmentation,in which the sequential fragmentation channel is dominant.These three fragmental ions are produced almost instantaneously in a single dynamic process for the non-sequential fragmentation channel but stepwise for the sequential fragmentation.In the first step,the weak van der Waals bond breaks,(CO_(2))_(2)^(4+)dissociates into two CO_(2)^(2+)ions;and then one of the C=O covalent bonds of CO_(2)^(2+)breaks up,the CO_(2)^(2+)ion breaks into CO^(+)and O^(+).The time interval between the two steps is longer than the rotational period of the intermediate CO_(2)^(2+)ions,which is demonstrated by the circle structure exhibited in the Newton diagram.We find that the sequential fragmentation channel plays a dominant role in the three-body Coulomb explosion of(CO_(2))_(2)^(4+)ions in comparison of the event ratio of the two fragmentation channels.