Chemical reactions, laser stimulated

The combination of ion traps with lasers has opened up a wide range of innovative experiments. In addition to the information obtained from detecting reemitted or stimulated photons, there are many laser based schemes for probing or manipulating a trapped ensemble including optical pumping, laser induced dissociation, or light stimulated chemical reactions. Lasers are utilized for state specific creation of ions in the trap. 

Early field ion emission studies of gas-surface interactions use field ionization mass spectrometry. Gas molecules are supplied continuously to the tip surface by a polarization force and by the hopping motion of the molecules on the tip surface and along the tip shank. These molecules are subsequently field ionized. The role of the emitter surface in chemical reactions is not transparent and has not been investigated in detail. Only in recent pulsed-laser stimulated field desorption studies with atom-probes are these questions addressed in detail. We now discuss briefly a preliminary study of reaction intermediates in NH3 formation in pulsed-laser stimulated field desorption of co-adsorbed hydrogen and nitrogen,... 

Since it has been shown that in many exothermic reactions a large part of the energy liberated enters the vibration of the newly formed molecule, there has been considerable interest in developing vibrational lasers pumped by chemical reaction. Although a total inversion between vibrational states is not required [223], it is difficult to reach the threshold condition for lasing action if relaxation is faster than excitation by reaction. These effects can be reduced where a light flash (or pulsed discharge) initiates reaction, and stimulated emission has now been observed from a number of systems [224]. 

The large Einstein radiative coefficients [225] and the widely spaced vibration-rotation quantum states make HF peculiarly prone to stimulated emission, and a large proportion of the chemical lasers which have been reported operate on lines in the infrared bands of this molecule [224], H-atom abstraction reactions by F and F-atom abstraction by H are both normally exothermic, and HF is quite generally produced in a vibrational distribution giving rise to oscillation. However, the systems are complex frequently both types of reaction occur, and the details of the vibrational distribution resulting from chemical reaction are difficult to evaluate. 

Recent research focus now on applying FTIR methods to proteins without an intrinsic chromophore. In investigating oncogenic hras p21, for instance, protein activity is stimulated with a photolabile substance such as caged GTP (Fig 6.6-21). A UV laser flash, which separates the head group and releases GTP, triggers the GTPase activity of p21 This new experimental approach offers now a very broad applicability to study chemical reactions by time-resolved FTIR. 

In the Chemical Vapor Deposition (CVD) methods, the starting material undergoes specific chemical reactions at the hot surface of the substrate to form thin layers of the desired material. The reaction can be stimulated by various energy sources, e.g. plasma, giving plasma enhanced CVD (PECVD), or a laser, giving laser CVD. 

Laser-induced reaction has been widely used to stimulate gas-surface interaction. Lasers are also used to probe molecular dynamics in heterogeneous systems as well. In the applied area, the laser photochemical techniques are successfully applied to produce well defined microstructures and new materials for microelectronic devices (1). Enhanced adsorption and chemical reaction on surfaces can be achieved by a photoexcitation of gaseous molecules, adsorbed species as well as solid substrates. The modes of the excitation include vibrational and electronic states of the gaseous species and of the adsorbates surface complexes. Both a single and a multiple photon absorption may be involved in the excitation process. 

So, the studied liquids absorb 1+2 photons, but to excite their molecules first electron levels it needs 5-6 photons because they are in the region of 180-220nm. Therefore one may assume that vibrational levels excitation ( 2ev) occurs which is enough to realize chemical reactions with formation of new, as well gas like products in condensed mediums. It is probable that the nature of reactions products will depend on the stimulation mechanism thermal way or induced by high intensivity laser action. So such studies are actual because they are opening new ways to realize purposeful reactions, in particular synthesis. 

To use high intensivity lasers emissions as sources of chemical reactions stimulators it is indispensable to take into consideration the boundaries of the applicability concerning their intensities with respect to each reagent separately. Only such approach can guarantee to obtain correct experimental data. 

K. Kleinermanns, J. Wolfrum, Laser stimulation and observation of elementary chemical reactions in the gas phase. Laser Chem. 2, 339 (1983)... 

The KPS paper stimulated research in several new directions, and ultimately spawned new fields. Many researchers, including Karplus, got interested in the development of QST of chemical reactions, and this led to accurate quantum descriptions of the H + H2 reaction [8] a decade after the KPS paper. There was also significant interest in the application of QCT methods to gas-phase reactions other than H -f- H2, and in fact this approach is now considered to be a standard research tool for studying gas-phase reaction dynamics of relevance to laser chemistry, combustion chemistry, atmospheric chemistry, and other applications. 

Laser-stimulated versus laser-induced chemical reactions... 

Chemical reactions can be stimulated or induced by lasers. The former case refers to the situation where... 

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