中文摘要：

利用飞行时间质谱（TOFMS）研究碘甲烷分子激光电离的过程中,发现I＋离子峰的峰形随激光光强增大逐渐加宽,且CHq＋（q=0～3）离子峰位置随光强增大而发生移动。激光功率密度从1.4×1010 W/cm2增加到5.2×1010 W/cm2时,I＋离子峰的半高全宽W1/2从113ns增加到426ns,同时CH3＋离子的峰位置向前位移了52ns。通过对I＋离子峰的半高全宽W1/2和CH3＋离子峰位置与碘离子强度II＋关系的分析,发现I＋离子峰的半高全宽W1/2正比于II＋0.5,而CHq＋（q=0～3）的峰位移与碘离子的强度II＋成正比。激光焦点处离子间的库仑排斥作用随着离子强度的增大而增大,由于这种空间电荷效应造成的库仑势能的增加对离子的初始平动能有一定影响,并导致离子到达检测器的时间发生改变,因而半高全宽的增大和离子峰位移随离子强度的变化规律,可以用空间电荷效应来解释。

英文摘要：

The multiphoton ionization of CH3I molecule with 532 nm nanosecond laser was studied by a homemade laser ionization time of flight mass spectrometer. The influence of laser intensity on the full width at half maxi of CHq＋ （q= 0 - 3） ions were investigated from 1.45〈 10^10 W/cm2 to 5.2×10^10 W/cm2, mum W1/2 in details. of I＋ ion peak and the peak position Wh the W1/2 of I＋ en laser intensity was increased ion was broaden from 113 ns to 426 ns, while the peak position of CH3 ＋ was shifted forward about 52 ns. Through formula derivation and the linear fitting between the peak broadening, peak shift and intensity of I＋ ion, the W1/2 of I＋ ion is proportional to I＋0.5, while the peak shifts of CHq＋ （q=0-3） were proportional to I1＋ At the laser focus, the Coulomb repulsion among the ions increases with the increasing of ion intensity, and the Coulomb potential due to the space charge effect has an influence on the ion kinetic energy, which results in the change of the time of ion reaching the detector. The peak broadening and shift of ions can be well explained by space-charge effect.