Trapping, laser-induced

Mobility of this second kind is illustrated in Fig. XVIII-14, which shows NO molecules diffusing around on terraces with intervals of being trapped at steps. Surface diffusion can be seen in field emission microscopy (FEM) and can be measured by observing the growth rate of patches or fluctuations in emission from a small area [136,138] (see Section V111-2C), field ion microscopy [138], Auger and work function measurements, and laser-induced desorption... 

S. Coussan, A. Loutellier, J. P. Perchard, S. Racine, A. Peremans, A. Tadjeddine, and W. Q. Zheng, Infrared laser induced isomerization of methanol polymers trapped in nitrogen matrix. 

Wiegand Steubing, R., Cheng, S., Wright, W. H., Numajiri, Y., and Bems, M. W. (1991) Laser induced cell fusion in combination with optical tweezers the laser cell fusion trap. Cytometry 12, 505-510. 

Separation and detection techniques for antibacterials in food mainly focus on the use of LC coupled to MS or tandem MS. Nevertheless, recent studies have suggested capillary electrophoresis coupled to laser-induced fluorescence (LIE) as a way of improving sensitivity [49], HRLC coupled to microTOF-ESI-MS as a highly selective, sensitive, and quick screening method for 100 veterinary drugs in fish, meat, and egg samples [195], and nanoscale LC coupled to UV or ion trap MS, with LODs in the range 0.01-0.51 pg/L (nanoLC-MS) and the possibility that even lower limits could be achieved by using triple quadrupole MS [59]. 

Mathivanan, Johnston and Wayner examined the effect of substituents on the rates of cleavage of a-phenoxyacetophenone radical anions (equation 6)43. In this study, the radical anions were generated by trapping solvated electrons produced by laser-induced photoionization of 4,4 -dimethoxystilbene in CH3CN and DMF. Their results show that the fragmentation rate is enhanced when Y is electron withdrawing, but retarded when X is electron withdrawing. 

Steroids (neutral or conjugated) and their dansylhydrazine derivatives Polyacrylic gel-based macroporous particles Acetonitrile-water-240 mM ammonium formate buffer, pH 3 (55 40 5) (also gradient elution) 350 mm x 100 pm i.d. 250 mm active length, laser induced fluorescence detection or coupling with electrospray-ion-trap mass spectrometry... 

A particularly important variant of the optical force, interparticle forces, turns out to be crucial for SERS. This effect is similar to the attractive van der Waals force between small particles, which is due to interactions between spontaneously fluctuating dipoles, but the optical interaction is due to coupling between the actual particle dipoles induced by the trapping laser. Due to the interparticle optical forces, metal nanoparticles aggregate in an optical tweezers and produce hotspots, i.e., particle junctions with intense local fields for SERS. Raman probes can be excited either by the trapping laser or, preferably, by a separate low power beam that does not disturb the trapping. 

The dimerization is easily understood considering the optical potential created by the trapping laser. Figure 18.2b shows the calculated optical potential experienced by a silver nanoparticle that is fi ee to move in a Gaussian laser focus at a wavelength of 830 nm. The particle is also affected by the optical interparticle force from an immobilized silver particle located at different separations from the laser focus. It is clear that a deep potential minimum is induced when the trapped particle approaches the immobilized one, giving rise to spontaneous optical dimerization and a SERS hot spot in the optical trap. Note that the two particles are expected to ahgn parallel to the laser polarization in this case, as has been demonstrated experimentally recently [88]. 

Among the most interesting outcomes of these studies were the results of Jamjan Rajikan [132] (now professor of chemistry in the University of Science, Malaysia) on the laser-induced spectra at liquid helium temperature of anthracene deliberately doped with 2-hydroxyanthracene. This is a persistent impurity in crystalline anthracene, and signs of it could be seen in almost all the published spectra. Spectra at low temperature showed two distinct traps characteristic of the impurities themselves, each accompanied by satellites thought to be X-traps [217],... 

In the second paper, O Dell et al discuss Bose-Einstein condensates with laser-induced dipole-dipole interactions. A Bose-Einstein condensate formed in a trapped ultracold atomic vapour constitutes an example of macroscopic... 

Jiang, Y., Matsumoto, Y., Hosokawa, Y., Masuhara, H. and Oh, I. (2007) Trapping and manipulation of a single micro-object in solution with femtosecond laser-induced mechanical force. Appl. Phys. Lett., 90, 061107-061103. 

Vibrational frequencies for example result from the appUcation of infrared, laser-induced fluorescence, Raman, and Raman resonance spectroscopy. Spectroscopy in the visible and near-UV regions yields information on electronic transitions. Electron spin resonance spectroscopy is used in determining the geometric and electronic structure. These methods were applied to study the gaseous species trapped at low temperatures in a solid inert rare gas matrix (matrix isolation technique) as well as in the free state. 

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