Transfer chemical laser

In some cases the measured V-V transfer rates differ from theoretical predictions, which indicates that some improvement is needed in theoretical models. Sophisticated computer analysis has to be employed to transform the experimental data to theoretical parameters The spectroscopic studies of cw and pulsed chemical lasers including the local variation of laser output on different vibration-rotation transitions as a function of distance froih the injectory array has been a useful tool, too, for elucidating the different reaction paths and the excited molecular levels involved... 

Cage effect, solvent, 169, 216, 227 Calvin cycle, 283 Character table, 36 Charge transfer complexes, 83 from metal to ligand, 269 interaction, 286 intramolecular transitions, 85 ligand to metal (CTLM), 269 mechanism. 182 transition, characteristics of, 85 transitions, to solvent, 86, 102, 276 Chemical lasers, 222 spectroscopy, 230 Chemiluminescence, 160, 265 reactions, 266... 

There is a complex interplay of kinetic processes in these energy transfer lasers. The conditions under which they operate are extreme in terms of the concentrations of transient species and the local gas temperatures. Many of the key reactions are difficult to study in isolation as they involve interactions between pairs of radicals or other transient species (e.g. collisions between electronically and vibrationally excited molecules). The impetus to obtain mechanistic and kinetic data for chemical laser systems (potential as well as demonstrated) has stimulated the development of new experimental techniques and produced a substantial body of kinetic data. Beyond the practical value of this work, the kinetic data that have been obtained are of fundamental scientific interest. They provide insights regarding the underlying principles that govern energy transfer processes and rare examples of reactions involving electronically and/or vibrationally excited species. 

A considerable data base of quenching and energy transfer rate constants for NF(a) and NF(6) has been established. Many of the reactions of importance for chemical laser systems have been determined, although the greater majority of these measurements have been made at room temperature. As noted in Sec. 7.1, it will be of interest in future studies of NF kinetics to examine the temperature dependencies of the rate constants. 

In related experiments, COF, (formed in situ) has been shown to reduce the output power of DF-CO, transfer chemical lasers [553,611]. These lasers, which achieve population inversion by intermolecular energy transfer to the asymmetric stretching mode of CO, viz. 

This article deals with a field of research on the borderline between physical chemistry and laser physics. As it is intended to combine aspects of both areas, molecular amplifiers based on partial or total vibrational inversion are first characterized in general, after which the generation, storage, distribution, and transfer of vibrational energy in chemical processes is reviewed. There is a brief discussion of the experimental requirements for laser oscillation and associated hardware problems. Experimental results for specific chemical laser systems are then surveyed and the prospects for high-power chemical laser operation considered. The concluding sections are devoted to the contribution of chemical lasers to reaction kinetics and their other uses in chemistry. 

There are several ways of creating the requirednon-equilibrium situation, chemical reactions being one way. Chemical lasers are thus defined as lasers where a population inversion is effected by selective chanelling of the energy of a chemical reaction into certain excited product states. We also include in this discussion lasers which are pumped by energy transfer from a chemically excited species to an admixture which is then capable of lasing, and lasers... 

Earlier than with pulsed chemical lasers, the first technological breakthrough in chemical lasers occurred for continuous-wave lasers. Almost simultaneously in 1968 two groups successfully operated continuous-wave chemical lasers. One was at the Aerospace Corporation headed by T. A. Jacobs 75>, the other one at Cornell University under T. A. Cool 76>. One of these lasers was an HF laser the other was that is now called a hybrid chemical laser, being pumped by energy transfer rather than by a direct chemical reaction. This laser principle has been described in the context of pulsed chemical lasers in Section 6.5, In addition to these devices, an HF cw laser having millisecond flow duration was also demonstrated in principle in a shock tunnel. The latter employed diffusion of HC1 into a supersonic stream containing F atoms 77>. 

Efficient, purely chemical laser operation is possible in hydrogen halide-CO2 transfer lasers, as developed by Cool and coworkers 83>. In these lasers no external energy sources are required. The systems, which operate on the mixing of commercially available bottled gases, are HC1—CO2, HBr—COg, DF— CO2, and HF—CO2. The pumping scheme for a DF—CO2 laser, for instance, is as follows ... 

The preparation of nonequilibrium level or species populations is the first step in any kinetic experiment. The introduction of lasers to chemical research has opened up new possibilities for preparing, often state-selectively, the initial nonequilibrium states. However, the subsequent time evolution of the molecular populations occurs almost invariably along several relaxation pathways. Some of which, like intra- and intermolecular vibrational energy transfer in infrared multiphoton absorption experiments, may interfere with the exciting laser pulse and/or with the specific process investigated. In such cases, as in chemical laser research, one has to interpret the behavior of complex nonequilibrium molecular systems in which the laser radiation plays of course a major role. This establishes the link between the present article and the general subject of this volume. 

The oxygen-iodine chemical transfer laser, 02( A) + I( / 3/2) 02( 2)+ I( /, /2)> based on the same electronic transition as the iodine photochemical laser, I( 7, /2) I( 3/2). and a few systems operating on pure rotational transitions are among the recent developments in chemical laser research. Other electronic lasers such as the iodine photochemical laser and the large group of excimer lasers are also classified sometimes as chemical lasers. Yet, most chemical laser systems utilize vibrotational transitions, almost exclusively of diatomic molecules. Our discussion will be confined to this type of chemical lasers. To emphasize the nonequilibrium characteristics and the time factor we shall consider only pulsed lasers. We shall not discuss important subjects such as optical properties, gas dynamic factors, and computational methods. As specific guiding examples we shall refer to the well-studied F-l-H2->HF-h H laser and the relatively simple (only one active vibrational band) Cl -I- HBr- HCl -I- Br system. ... 

Energy Efficiency of Chemical Lasers Chemical Lasers with Excitation Transfer... 

T.A. Cool, Transfer chemical laser, in Handbook of Chemical Lasers, ed. by R.W.F. Gross, J.F. Bott (Wiley, New York, 1976)... 

An extremely metastable excited state is not itself a suitable laser candidate because the optical gain is directly proportional to the radiative rate. One is faced with a dilemma If the only states diat can be efficiently produced are extremely long lived, how can one hope to build a laser A possible solution to this problem is found in the only electronic transition chemical laser yet demonstrated, the chemical oxygen iodine laser (COIL). In the COIL chemically produced, highly metastable 02( A) resonantly transfers energy to atomic iodine, and an inversion is produced between the Pi/2 and P3/2 iodine levels and atomic lasing occurs at 1.315 im. This laser was predicted by Derwent and Thrush [11] in 1972 and was demonstrated by McDermott et al in 1977 [12]. This device has been described in numerous papers [12-16], and we do not discuss it further. It clearly demonstrates the concept of a transfer-laser and may serve as a model for future visible lasers using this two step approach. 

As an example of a potential visible chemical laser based upon energy transfer, we consider the inteihalogen molecule IF. In this regard the (B X) system of IF has received considerable attention in recent years. Indeed several papers contained in this volume describe details of chemical excitation processes in IF. 

Efficient excitation of excited electronic states is only achieved by energy transfer from a metastable species, i.e. 02( A). The O2-IF system provides an interesting example in which these two processes are both utilized. The vibrational excitation in IF(v) opens pathways for 02( A) transfer that would otherwise be energetically inaccessible. ether this system can eventually be developed into an actual laser system remains to be seen. It does however provide interesting insights into selective chemical excitation of electronic states. In this brief survey we have attempted to discuss important issues relevant to chemical excitation of electronic states. The dominant obstacle that has delayed the development of short wavelength chemical lasers is the paucity of reactions that efficiently produce excited electronic states, and this remains the area needing the most attention. 

Partially because of last minute cancellations, several important topics have not been included in the present work. Papers on fluorine atom chemical lasers, high-energy fluorine atom reactions, and classical trajectory simulations of hydrogen transfer reactions by atomic fluorine are conspicuously absent. Other more speciahzed topics not included were olefin addition reactions by fluorine-rich carbenes, H2/F2 explosions, unimolecular reaction d3mamics of fluorine-containing aliphatic radicals, and high-power fluorine atom lasers in energy research. 

In the experiment shown in Figure 9.1a mixture of HCl and DCl in an excess of Ar buffer gas is irradiated by a brief pulse of infrared light (say, from an HCl chemical laser. Section 9.0.3). HCl molecules are thereby selectively excited from the V = 0 to the v = 1 level. Thereafter, the population of the HCl(v = 1) level is depleted both by transfer of its entire vibrational energy to rotation and trans-... 

Figure 9.8 Level diagram appropriate for the N2—CO2 chemical laser. Vibrationally excited N2 molecules are the source of the excitation of CO2(001). The final states of the laser emission, CO2(100) and C02(020), are depleted by V—V transfer. See Figure 9.7 for the relevant levels of CO2.

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