Method crossed molecular beams

In this chapter, the information available from crossed beam experiments on the reactions of CN radicals with simple unsaturated hydrocarbons leading to the formation of unsaturated nitriles will be reviewed after a brief introduction on the crossed molecular beam method. The results presented here are part of a systematic study which has been undertaken to characterize the reactions of CN radicals with small unsaturated organic molecules at the microscopic level [60,75-84]. 

The elementary reaction OH -h CO CO2 + H is the primary mechanism for formation of CO2 in combustion. This reaction, as well as its reverse, have been studied extensively using a variety of methods, including the crossed molecular beams method. The reaction is thought to involve the participation of long-lived HOCO intermediates, as illustrated in Fig. 14. Note that although OH -h CO may form the intermediate complex with at most only a small potential energy barrier, a substantial barrier exists for H-atom loss forming CO2. 

The value of the magnetic hyperfine interaction constant C = 22.00 kHz is supposed to be reliably measured in the molecular beam method [71]. Experimental data for 15N2 are shown in Fig. 1.24, which depicts the density-dependence of T2 = (27tAv1/2)-1 at several temperatures. The fact that the dependences T2(p) are linear until 200 amagat proves that binary estimation of the rotational relaxation rate is valid within these limits and that Eq. (1.124) may be used to estimate cross-section oj from... 

Another popular method for studying combustion species is via crossed molecular beams. In this technique, the reactant molecules of interest are propelled as beams toward an intersection where their molecular collisions bring about reactions. For a more complete discussion of crossed molecular beam experiments, see reference 59. 

Undoubtedly, the technique most suited to tackle polyatomic multichannel reactions is the crossed molecular beam (CMB) scattering technique with mass spectrometric detection and time-of-flight (TOF) analysis. This technique, based on universal electron-impact (El) ionization coupled with a quadrupole mass filter for mass selection, has been central in the investigation of the dynamics of bimolecular reactions during the past 35 years.1,9-11 El ionization affords, in principle, a universal detection method for all possible reaction products of even a complex reaction exhibiting multiple reaction pathways. Although the technique is not usually able to provide state-resolved information, especially on a polyatomic... 

In this chapter we have discussed the successful implementation in our laboratory, for the first time, of the soft (i.e. low energy) electron-impact ionization method for product detection in crossed molecular beams reactive scattering experiments with mass spectrometric detection. Analogous to the approach of soft photoionization by tunable VUV synchrotron radiation,... 

One of the first approaches to study the microscopic kinetics i.e. state-to-state cross sections and reaction probabilities of a chemical reaction was the crossed molecular beam experiments. The principle of the method consists of intersecting two beams of the reactant molecules in a well-defined scattering volume and catching the product molecules in a suitable detector (Fig. 9.33). 

HF.RSCHBACH. DUDLEY R. (1932-). Awarded the Nobel prize in chemistry in 19X6 for work reporting that the energies of reactions of crossed molecular beams of isolated alkali metal atoms and alkyl halide molecules appeared mostly as vibrational excited states of products. This method ol studying all types of chemical reactions led to a more detailed knowledge of reaction processes. Doctorate awarded from Harvard in 1958. 

Harpoon reactions of alkaline metal atoms with halogen molecules in the gas phase seem to be the first instance of the observation of chemical electron transfer reactions at distances somewhat exceeding gas-kinetic diameters. Actually, as far back as 1932, Polanyi, while studying diffusion flames found for these reactions cross-sections of nR2, somewhat exceeding the gas-kinetic cross-sections [69]. Subsequently, more precise measurements which were carried out in the 1950s and 1960s with the help of the molecular beam method, confirmed the validity of this conclusion [70],... 

Vibrational product state distributions have been obtained for reactions studied in crossed molecular beams using the technique of beam electric resonance spectroscopy [109]. This method uses the focusing action of electric quadrupole and dipole fields to measure the radio frequency Stark spectrum of the reaction products, which must possess a dipole moment. This has restricted this technique to reactions producing alkali halides. 

In 1969 it was still possible to consider separately the results of experiments carried out with crossed molecular beams and spectroscopic measurements of the product states of bulb reactions. Not only had there been few attempts to fuse together these two techniques, but also the lists of reactions which, up to that time, had been studied by the two methods were almost mutually exclusive. One result of progress in the 1970s is that this clear distinction has now been removed. The operation of crossed-beam apparatus... 

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