High resolution applications of laser-induced breakdown spectroscopy for environmental and forensic applications

Laser-induced breakdown spectroscopy (LIBS) has been used in the elemental analysis for a variety of environmental samples and as a proof of concept for a host of forensic applications. In the first application, LIBS was used for the rapid detection of carbon from a number of different soil types. In this application, a major breakthrough was achieved by using a multivariate analytical approach that has brought us closer towards a “universal calibration curve”. In a second application, it has been demonstrated that LIBS in combination with multivariate analysis can be employed to analyze the chemical composition of annual tree growth rings and correlate them to external parameters such as changes in climate, forest fires, and disturbances involving human activity. The objectives of using this technology in fire scar determinations are: 1) To determine the characteristic spectra of wood exposed to forest fires and 2) To examine the viability of this technique for detecting fire occurrences in stems that did not develop fire scars. These examples demonstrate that LIBS-based techniques are inherently well suited for diverse environmental applications. LIBS was also applied to a variety of proof of concept forensic applications such as the analysis of cremains (human cremation remains) and elemental composition analysis of prosthetic implants.     

Laser pyrolysis micro-spectroscopy for modelling fire-induced degradation of ethylene-vinyl acetate systems

A recently developed laser pyrolysis (LP)-Raman/ATR micro-spectroscopic method was applied for analyzing the degradation of polymer systems. The concept behind the method is to combine the micro-scale modelling of fire circumstances with analytical monitoring of the chemical changes in the solid phase of the sample. Samples were irradiated with the infrared beam of a CO₂ laser. The chemical changes were determined by micro-Raman/ATR spectroscopy methods in 200 ms intervals. The applicability of the method is demonstrated here through the pyrolysis of EVA and EVA composites containing metal-modified clays. Rapid depth profiling of few milligrams of sample is feasible with Raman detection, while the ATR sensor is applicable for analysis of fluorescent samples such as Fe coated sepiolite. The acceleration effect of montmorillonite and sepiolite minerals on the degradation of EVA is more pronounced if their surface is coated with Fe atoms. The effects of laser and the cone heater on the ratio of characteristic Raman bands of the polymer are compared and found to be in good correlation.     

Laser Raman and IR spectra and force fields for 2,6-difluorobenzonitrile

Raman spectrum of 2,6-difluorobenzonitrile in the powder form has been recorded in the region 50–4000 cm⁻¹ on a Jasco K-500 spectrophotometer using the 488.0 nm radiation from an argon laser. IR spectra in the region 200–4000 cm⁻¹ have been recorded in KBr pellet and nujol mull on a Nicolet DX spectrometer and in liquid and vapour phases on a Jasco FTIR/7000 spectrometer. Using these observed frequencies force field calculations for the planar and non-planar modes have been carried out assuming a general valence force field.     

Real-time monitoring of Yb vapor density using an extended cavity violet diode laser

Based on laser absorption spectroscopy (LAS), we developed a vapor density monitor for controlling the vaporization rate of Yb using a tunable diode laser. The laser source consisted of an extended cavity violet diode laser which has an emission wavelength of 398.8 nm coincident with the Yb absorption transition line, 6s(2) 1S(0)-6s6p 1P(1). The light emitted from the diode laser was transmitted across an atomic vapor column generated by heating the Yb metal, while the laser frequency was scanned across the atomic transition line. By comparing the amount of incident light to the amount of light transmitted after the light passed through the vapor column, the vapor density was determined using the Beer's law. From the experimental results, we demonstrated that the diode-laser-based LAS operated successfully for the real-time monitoring of the Yb vapor density.     

Features in the vibrational relaxation of laser excited Freon-22 molecules

The vibration-translation (V-T) of laser excited Freon-22 (CF₂HC1) molecules has been studied. An interferometric technique allows simultaneous measurement of the initial energy 〈E〉 stored in the molecules, and of the V-T relaxation time. Consequently, the V-T relaxation time and the energy released per collision can be determined as a function of the energy absorbed from the laser field. Three distinct regions have been observed for these dependences. This behaviour observed and reported by us for Freon-22 confirms the role played in the relaxation process by the initial distribution of the vibrational energy, and agrees qualitatively with the experimental results for other polyatomic molecules.     

纳米级无机聚钼酸盐“二级有序聚集体”

介绍了纳米级水溶性无机聚钼酸盐分子的逐步生长合成, 对近年来水溶液中纳米级无机聚钼酸盐分子的奇特自聚集行为进行了简述, 从两亲分子“有序聚集体”概念的角度, 提出了水溶性纳米级无机聚钼酸盐“二级有序聚集体”的概念.     

液相脉冲激光烧蚀法制备高熔点的纳米金属粒子

采用液相脉冲激光烧蚀法成功地制备了高熔点的金属Pt、Ru与Ag纳米粒子. 采用SEM、TEM、ED和紫外-可见吸收光谱表征了纳米粒子的特征. 纳米粒子的粒径基本在数个到数十个纳米的大小范围内. 发现含适量PVP(poly(vinylpyrrolidone))的水溶液有利于纳米粒子的制备, 而且还能够提高纳米粒子悬浮液的稳定性. 该制备方法较简单, 在制备高熔点的纳米金属粒子方面有着其它方法所不能比拟的优势.     

激光双光子电离方法对水溶液表面的蒽及其衍生物的测定

激光双光子电离方法用水溶液表面的蒽及其衍生物分子的检测，Ｎｄ－ＹＡＧ激光的第三谐波３５５ｍ用作激发和电离。光电离电荷数在－３个数量级内随浓度呈线性关系。     

C70正负离子的激光引发聚合

Ｃ_（７０）正负离子的激光引发聚合刘朝阳，王春儒，黄荣彬，林逢辰，郑兰荪（固体表面物理化学国家重点实验室，厦门大学化学系，厦门，３６１００５）关键词Ｃ_（７０），聚合，激光等离子体Ｃ６０在激光作用下的进一步聚合是近来在Ｃ６０研究中的又一重要发现，Ｙｅｒ...