Infrared laser pyrolysis

The limited knowledge of thermal behaviour of halogenated acids has been extended significantly by a pyrolysis (infrared laser-powered) and semiempirical study which has established that mono-, di- and tri-chloroacetic, trifluoroacetic, and bromoacetic acid eliminate HX and that both bromo- and iodo-acetic acid undergo C—X bond homolysis acetic acid undergoes decarboxylation and dehydration under the same conditions.46 The semiempirical calculations of corresponding activation energies are consistent with these conclusions. 

Nitrogen-containing explosives [249] and trinitrotoluene [250] have been determined in soil by gas chromatography with thermionic NP detection and reverse-phase high-performance liquid chromatography. Warmont et al. [251] used tunable infrared laser detection to study the pyrolysis products of explosives in soil. 

The use of phosphorus-based flame retardants in combination with other, better established, flame retardants is most effective in situations in which the combination proves synergistic. However, as yet our understanding of such synergistic effects is far from complete and more fundamental work is required in this area Work in which the gaseous and solid products of combustion, with and without the presence of flame retardants, are carefully analyzed. Such analyses can now be undertaken more readily than in the past, owing to the relatively recent development of techniques such as gas-phase FT-infrared spectroscopy and laser-pyrolysis time-of-flight mass spectrometry for the identification of volatiles, and solid-state NMR spectroscopy and x-ray photoelectron spectroscopy for the analysis of chars. 

In the past, this type of selective photolysis has been accomplished by exciting a rather complex precursive molecule with infrared laser radiation at a frequency which could select some initial vibrational mode of absorption that would ultimately lead to the desired product. Many of the impressive results that have been achieved with this approach have been summarized in a recent review (1). Unfortunately, two general difficulties have persisted in the conventional approaches. The first has been the tendency to obtain pyrolysis of the parent molecule rather than photolysis. The second is that if viewed as reactive species, laser photons are extremely expensive "substances," their cost being elevated further by the degree of spectral purity and stability that must be maintained. Both... 

Finally, laser pyrolysis of Fe(CO)s produces partially or fully oxidized Fe nanoparticles of 20 nm mean diameter using an infrared laser in mixtures containing SF. A similar procedure carried out in isopropanol produced 5 nm nanoparticles of 7-Fc203. ... 

In laser pyrolysis, a precursor in the gaseous form is mixed with an inert gas and heated with CO2 infrared laser (continuous or pulsed), whose energy is either absorbed by the precursor or by an inert photosensitizer such as SFs. Swihart [84], Ledoux et al. [116,117], and Ehbrecht and Huisken [118] prepared Si nanoparticles by laser pyrolysis of silane. By using a fast-spinning molecular beam chopper, Si nanoparticles in the size range of 2.5-8 nm were deposited on quartz substrates to study quantum confinement effects [116]. Li et al. [119] improved the stability of the Si nanoparticles ( 5 nm) by surface functionalization and obtained persistent bright visible photoluminescence. Hofmeister et al. [120] have studied lattice contraction in nanosized Si particles produced by laser pyrolysis. The method has been used to synthesize metal nanoparticles as well (see Table 2.1). Zhao et al. [121] obtained Co nanoparticles by laser pyrolysis of Co2(CO)s vapor at a relatively low temperature of 44° C. Ethylene was used as a photosensitizer for CO2 laser emission. Nanoparticles... 

A new method for the quantitative determination of pesticides is laser-pyrolysis scanning (LPS). No color reaction or visualization procedure is necessary simply the TLC plates are placed in a chamber after development and irradiated with an infrared laser to produce a high temperature at the location of the spot. The analyte is swept by a carrier gas to a gas chromatograph and analyzed by an appropriate sensitive GC detection method. 

When NH3 and ND3 were photolyzed in the infrared region (CO2 laser) electronically excited fragments were also observed [84, 85]. In the infrared multiphoton dissociation (IRMPD) of ND3, the imidogen radical is formed in both the spin-forbidden (X and the spin-allowed (a A) states [86, 87]. In a CO2 laser pyrolysis experiment, in which a mixture of SFg, CF4, and NH3 was irradiated, ground-state NH radicals were produced [88]. 

Alexandrescu, R., I. Moijan, M. Scarisoreanu et al. 2010. Development of the IR laser pyrolysis for the synthesis of iron-doped Ti02 nanoparticles Structural properties and photoactivity. Infrared Phys. 

Schnaiter M, Henning T, Mutschke H, Kohn B, Ehbrecht M, Huisken F Infrared spectroscopy of nano-sized carbon grains produced by laser pyrolysis of acetylene analog materials for intersteUar grains, Astrophys J 519 687-696, 1999. 

L2MS has been used to directly analyze additives in a range of polymers [41]. The L2MS method decouples the desorption and the ionization step in order that each step can be optimized. An infrared laser at 10.6 p,m is used to irradiate the polymer and cause ablation through a pyrolysis mechanism. During this step, the polymer is thermally decomposed and ejected while the additives remain intact. With a delay time of about 20 p,s, the additives are then subjected to a selective ionization with a UV laser at 266 nm through a resonant two-photon ionization step. Finally, the ions are mass separated, and recorded in a time-of-flight mass spectrometer. 

A number of anomeric D-hex-2-ulopyranosyl azides have been synthesized and their photochemistry examined. For both a- and P-azides, the major photoproducts arise from cleavage of the C-2C-3 bond and migration of the C-3 carbon to the nitrene centre. Decomposition reactions of a glycidyl azide polymer have been induced by pulsed laser infrared pyrolysis and UV photolysis of thin films at 17-77 K and monitored by IR spectroscopy. The initial step is elimination of N2 and formation of imines, which decompose on warming, possibly with secondary polymerization. 

Therefore we decided to gather new data about the laser-induced decomposition of polyimide and contrast them with results from pyrolysis using the same experimental technique, i.e., diffuse reflectance infrared Fourier-transform (DRIFT) spectroscopy. 

Spectral methods based on UV-visible spectrophotometry, laser-induced breakdown spectroscopy (LIBS), infrared (IR), Raman, nuclear magnetic resonance (NMR) spectroscopy, mass spectrometry (MS), thermoanalytical and chromatographic methods, especially liquid chromatography (LC) or gas chromatography (GC) combined with pyrolysis are most common. 

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