Velocity distribution of products

Vance and Bailey [94] also carried out measurements of velocity distributions of product ions using a double mass-spectrometer system similar to the one used by Giese and Maier [95] combined with the retardation product-ion analysis by Menendez et al. [96]. They studied the charge transfer and dissociative charge transfer reactions of Hj and N2 with H2, as well as the reaction + H2 H3 + H, and the results yielded considerable new information on the reaction mechanism. 

As mentioned previously, the modified spectator stripping model (polarization model) of Herman et al. [103] explains the velocity distribution of products very well but does not predict the angular distribution, whereas the DIPR model explains both. Thus there had been no full comparison between the two models until Chang and Light [113] refined and extended the polarization model to yield the angular distribution of products as well. 

Not only the angular, but the velocity distribution of products can give important information on the nature and mode of decomposition of the complex. Indeed, contour plots, such as shown in Figs. 21 and 22, can provide a new way of studying the nature of unimolecular decay. Theoretical treatments relevant to this topic are available in nuclear physics and, more recently, for chemical systems. ... 

Rakitzis T P, Kandel S A and Zare R N 1997 Determination of differential-cross-section moments from polarization-dependent product velocity distributions of photoinitiated bimolecular reactions J. Chem. Phys. 107 9382-91... 

The Doppler-selected TOF technique is one of the laser-based techniques for measuring state-specific DCSs.30 It combines two popular methods, the optical Doppler-shift and the ion TOF, in an orthogonal manner such that in conjunction with the slit restriction to the third dimension, the desired center-of-mass three-dimensional velocity distribution of the reaction product is directly mapped out. Using a commercial pulsed dye laser, a resolution of T% has been achieved. As demonstrated in this review, such a resolution is often sufficient to reveal state-resolved DCSs. 

The bimodal velocity distribution of the 0(3Pj) fragments produced via the triplet channel in the UV photodissociation of ozone has also been observed by Syage41,43>46 and Stranges et al.AA at photolysis wavelengths of 226 and 193 nm, respectively. Both authors measured anisotropy parameters for the fast and slow product pathways separately. 

It is necessary, however, to maximize the intermediate olefin product at the expense of the aromatic/paraffin product which makes up the gasoline ( ). The olefin yield increases with increasing temperature and decreasing pressure and contact time. Judicious selection of process conditions result in high olefin selectivity and complete methanol conversion. The detailed effect of temperature, pressure, space velocity and catalyst silica/alumina ratio on conversion and selectivity has been reported earlier ( ). The distribution of products from a typical MTO experiment is compared to MTG in Figure 4. Propylene is the most abundant species produced at MTO conditions and greatly exceeds its equilibrium value as seen in the table below for 482 C. It is apparently the product of autocatalytic reaction (7) between ethylene and methanol (8). 

Schindler, R. N., M. Liesner, S. Schmidt, U. Kirchner, and Til. Benter, Identification of Nascent Products Formed in the Laser Photolysis of CH,OCI and HOC1 at 308 nm and around 235 nm. Total Cl-Atom Quantum Yields and the State and Velocity Distributions of CI(2P(), J. Photochem. Photobiol. A Chem., 107, 9-19 (1997). 

Since the velocities and angular distributions of products from collisional dissociations at low incident-ion energies have generally not been determined, the precise mechanism by which the products are formed is unknown. Thus in the collisional dissociation of H2+ with helium as the target gas, H+ may result from dissociation of H2+ that has been directly excited to the vibrational continuum... 

The intensity of signal transmitted to the detector is greatly improved by using time-of-flight methods instead of mechanical velocity selectors. The beam of product molecules is chopped into a sequence of short pulses and the molecules then travel a known distance before being detected. The time-of-arrival spectrum at the detector gives the velocity distribution of the products [30]. This method of velocity analysis is now widely used in studies of crossed-beam reactions [111]. 

Various methods have been proposed for measuring the product velocity distributions from the Doppler absorption profile of the laser-induced fluorescence from the products. In one case, it has been suggested [115] that the velocity distribution of the H atom from... 

Conventional molecular beam reactive scattering studies have excelled in the determination of the angular and velocity distributions of reaction products, but direct information on the internal state distributions has been sparse. One of the most important of the non-beam methods for learning about the partitioning of reaction energy into the internal degrees of freedom of the products has been infra-red chemiluminescence studies. Unfortunately, this technique has hitherto been limited to hydride compounds, principally hydrogen halides. We present an alternative technique based on electronic fluorescence spectroscopy. 

An optical technique involving Doppler spectroscopy can also serve to gain insight into the angular and velocity distributions of reaction products, as reviewed in Ref. [43]. Finally, the Doppler method has been associated with the imaging technique. This is the so-called Doppler-selected time-of-flight technique, which is the most powerful one to obtain information on the three-dimensional (3D) velocity and angular distribution of the reaction products [44-46]. 

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