分子离子碎裂过程中动能释放的校准方法

Methods of calibrating kinetic energy release in dissociation process of molecular dications

分子离子碎裂过程中,动能释放(KER)是一个重要的物理参量,通过研究其分布特征,可以获取母体离子态布居、分子结构、以及解离机制等信息.本文以CO2+→C++O+两体碎裂过程为例,详细介绍了KER的重构过程.利用C+离子的二维动量分布、KER与离子出射角度的关系,校准了影响KER重构的实验参数:飞行时间、飞行时间谱仪电压、位置坐标.校准过程中,只有当碎片离子的二维动量分布呈圆形或者KER与离子出射角的分布呈直线时,影响KER重构的参数才符合校准标准.

In the studies of fragmentation processes of molecules induced by extreme ultraviolet photons,intense laser fields,or charged particles,kinetic energy release(KER)is a key physical parameter.It can reveal the electronic states of the parent molecular ion,and provide an insight into the molecular structures and the dissociation dynamics.Therefore,it is essential to obtain the accurate KER spectrum for studying the fragmentation process of molecules.However,in the experiments using reaction microscope,experimental parameters such as the timeof-flight(TOF),the voltage of the TOF spectrometer and the detector image of the fragments have significant influence on the accuracy of KER determination.In this work,by taking the two-body fragmentation process of CO2+→C++O+induced by 108 keV/u Ne8+impact on CO molecules as a prototype,we introduce two methods to accurately calibrate the reconstructed KER spectrum.The first method is to employ twodimensional momentum spectra of C+ions obtained by slicing the momentum sphere.The parameters are correctly calibrated when the circular distribution of the two-dimensional ion momentum image is restored.The second method is to use the correlation spectra of the KER as a function of the emission angle of the C+ions to calibrate the experimental parameters,the calibration meets the required level only when the linear dependence of the emission angle on the KER is fulfilled.Then,calibrated KER spectrum is obtained for the dissociation process.By fitting the peak dissociated from the 3∑+ state of CO2+in the KER spectrum,the energy resolution is estimated at 0.24 eV under these experimental conditions.Although these two methods can be used to accurately calibrate the reconstructed KER spectrum,the second calibration method does not require particularly high data statistics,and is suitable for analyzing the processes with lower reaction cross section.Furthermore,this method is convenient for debugging the parameters.Both methods are reliable for parameter calibration and guarantee high accuracy KER for molecular fragmentation experiments in future.