Suppression of Fragmentation in Multiphoton Ionization Mass Spectrometry Using a Near-Infrared Femtosecond Laser as an Ionization Source
Suppression of Fragmentation in Multiphoton Ionization Mass Spectrometry Using a Near-Infrared Femtosecond Laser as an Ionization Source
复制标题
使用近红外飞秒激光作为电离源抑制多光子电离质谱中的碎片
作者：
A. Li;P. D. Thang;T. Imasaka;T. Imasaka
利用400、800和1200 nm的飞秒激光，研究了五氯苯的电离和破碎过程。由于激光的脉冲宽度比激发态的寿命短，因此在质谱中可以清楚地观察到分子离子，因为分子可以在弛豫之前从单线态电子激发态直接电离到三重态能级。在1200 nm处碎裂最小，而在800和400 nm处电离最小。事实上，在800 nm处，由于单电荷分子离子在该波长处的吸收带，双电荷分子离子非常突出。在400 nm处碎裂进一步增强，这可以解释为双电荷分子离子在400 nm处解离，具有更大的吸收带。多光子电离过程中出现的离子种类（即单电荷和双电荷的分子离子）的吸收特性强烈地影响了碎片化。
The ionization and fragmentation processes for pentachlorobenzene were examined using a femtosecond laser emitting at 400, 800, and 1200 nm. A molecular ion was clearly observed in the mass spectrum, since the molecule can be directly ionized from the singlet electronic exited state before relaxation to triplet levels, because the pulse width of the laser is shorter than the lifetime of the excited state. Fragmentation was minimal at 1200 nm, in contrast to ionization at 800 and 400 nm. Indeed, a doubly-charged molecular ion was prominent at 800 nm, owing to the absorption band of the singly-charged molecular ion at this wavelength. Fragmentation was further enhanced at 400 nm, which can be explained by the dissociation of the doubly-charged molecular ion having a larger absorption band at 400 nm. Fragmentation was strongly affected by the absorption character of the ionic species, i.e., singly- and doubly-charged molecular ions, appeared in the process of multiphoton ionization.