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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。
During the laser ionization of methyl iodide by TOFMS, the peak shape of I + ion peak broadened with the increase of laser intensity, and the position of CHq + (q = 0 ~ 3) ion peak increased with the increase of light intensity Large and moving. When the laser power density is increased from 1.4 × 10 10 W / cm 2 to 5.2 × 10 10 W / cm 2, the FWHM of the I + ion peak is increased from 113 ns to 426 ns, and the peak position of the CH3 + ions shifts forward by 52 ns. The full width at half maximum (W1 / 2) of I + ion peak is proportional to II + 0.5 and CHq + (q = 0 ~ 3) by analyzing the relationship between the full width at half maximum of W1 + The peak shift is proportional to the intensity of iodide ions, II +. The Coulomb repulsion between the ions at the laser focal point increases with the increase of the ionic strength. The increase of the Coulomb potential due to the space charge effect has some influence on the initial translational energy of the ions, and leads to the time when the ions reach the detector Changes, so the increase of full width at half maximum and the ion peak shift with the ionic strength of the law, can be used to explain the space charge effect.