高电荷态离子引起的富勒烯离子的碎裂

离子在与富勒烯的相互作用过程中会导致C60分子的激发。处于低激发态的C60r 离子通过发射中性C2分子或带电的轻团簇碎片Cn 等非对称碎裂方式来耗散激发能,但如果激发能很高,笼形的C60r 离子可能会彻底崩溃,而发生多重碎裂。C60r 离子的碎裂过程与其电荷态r及分裂势垒密切相关。低电荷态的C60r (r≤3)离子蒸发一个C2分子需要克服10.3 eV左右的势垒。随着电荷态的升高,发射带电的Cn 会变得越来越容易,并逐渐过渡到多重碎裂过程。另一方面,C60r 离子的碎裂机制还与激发方式有关,在直接正碰过程中,将C60分子当作固体薄靶来处理,通过分析不同价态的C60r 离子的碎片谱,发现母核的初始电荷态决定碎裂方式,由此获得一个可以表征激发能大小的可观测量——发射电子个数。

FRAGMENTATION OF C60r+IN ION-FULLERENE COLLISIONS

C60 can be excited in the ion-fullerene collisions.The C60r ions usually dissipate the internal energy by evaporating C2 unite or undergoing asymmetric fission.However,the multi-fragmentation will occur when the excited energy is large or the charge state is very high.The fragmentation of C60r depends on the charge state r and the fragmentation barrier.For low charged C60r ions,the evaporation is the dominant process and the barrier is about 10.3 eV.With the increasing of the charge state r,the fission barrier reduces and finally the multi-fragmentation becomes the dominant process.On the other hand,the fragmentation pattern of C60r also depends on the nature of the excitation mechanism in the frontal collisions(the projectile penetrates C60 cage).By analyzing the fragments spectra for each charge state r,we found the fragmentation pattern of a parent C60r is related tightly to its initial charge r,and the ejected electron number is a measurable parameter which allows us to estimate the excitation energy.