A new broadly tunable (7.4-10.2 eV) laser based VUV light source and its first application to aerosol mass spectrometry
A new broadly tunable (7.4-10.2 eV) laser based VUV light source and its first application to aerosol mass spectrometry
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DOI：
10.1016/j.ijms.2008.10.024
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发表时间：
2009-01-15
影响因子：
1.8
通讯作者：
Bertram, A. K.
中科院分区：
文献类型：
--
作者：
Hanna, S. J.;Campuzano-Jost, P.;Bertram, A. K.
研制了一种基于激光器的真空紫外光源，利用氙气共振增强四波差混频技术对大气气溶胶中的有机物进行近阈值电离。该光源提供高强度的VUV光脉冲（取决于波长，在10（10）至10（13）光子/脉冲的范围内，5 ns FWHM），具有从122 nm（10.2 eV）至168 nm（7.4 eV）的连续可调谐波长。该设置允许紧密（< 1 mm（2））和精确的聚焦（μ rad指向角可调节性），这是单颗粒检测所需的属性。所产生的真空紫外线通过定制的单色器与泵浦波长分离，从而确保高光谱纯度并最大限度地减少吸收损失。的源的性能，其特征在于使用有机分子在气相和最佳工作条件的报告。在气相测量中，光电离效率（PIE）曲线收集了7个不同的有机物种的电离能跨越整个波长范围的真空紫外光源。所测得的出现能量是非常接近的文献值的电离能为所有七个物种。单个咖啡因气溶胶的脉冲CO2激光器在离子阱质谱仪蒸发的分析证明了单粒子研究的源的有效性。收集直径低至300 nm的单个颗粒的质谱。这些小颗粒的出色信噪比特性使咖啡因的检测限为8 x 10（5）个分子，相当于单个75 nm气溶胶，或约为300 nm颗粒的1.5%。还测量了源自气溶胶的咖啡因的表观能量，发现为7.91 +/- 0.05 eV，与文献值非常一致。(C)2008 Elsevier B. V.保留所有权利。
A laser based vacuum ultraviolet (VUV) light source using resonance enhanced four wave difference mixing in xenon gas was developed for near threshold ionization of organics in atmospheric aerosol particles. The source delivers high intensity pulses of VUV light (in the range of 10(10) to 10(13) photons/pulse depending on wavelength, 5 ns FWHM) with a continuously tunable wavelength from 122 nm (10.2 eV) to 168 nm (7.4 eV). The setup allows for tight (< 1 mm(2)) and precise focusing (mu rad pointing angle adjustability), attributes required for single particle detection. The generated VUV is separated from the pump wavelengths by a custom monochromator which ensures high spectral purity and minimizes absorptive losses. The performance of the source was characterized using organic molecules in the gas phase and optimal working conditions are reported. In the gas phase measurements, photoionization efficiency (PIE) curves were collected for seven different organic species with ionization energies spanning the full wavelength range of the VUV source. The measured appearance energies are very close to the literature values of the ionization energies for all seven species. The effectiveness of the source for single particle studies was demonstrated by analysis of individual caffeine aerosols vaporized by a pulsed CO2 laser in an ion trap mass spectrometer. Mass spectra from single particles down to 300 nm in diameter were collected. Excellent signal to noise characteristics for these small particles give a caffeine detection limit of 8 x 10(5) molecules which is equivalent to a single 75 nm aerosol, or approximately 1.5% of a 300 nm particle. The appearance energy of caffeine originating from the aerosol was also measured and found to be 7.91 +/- 0.05 eV, in good agreement with literature values. (C) 2008 Elsevier B.V. All rights reserved.