Crossed molecular beam studies

Crossed-molecular-beam studies of differential scattering of metastable noble-gas atoms with ground-state noble-gas atoms or simple molecules is the major topic of this chapter. These studies have been carried out recently at several laboratories with the common goal of finding both real and imaginary parts of the interaction potentials to further our understanding of the dynamics of collision processes involving metastable noble-gas atoms. 

The more exoergic reaction Ba + NzO has a smaller reaction cross section ( 90 A2 or 27 A2) [347, 351] and crossed-molecular beams studies [349] show that the BaO product is backward-scattered with a large amount of internal excitation ((Fr) < 0.20). Laser-fluorescence measurements [348] of the BaO(X Z+) product for the reaction in the presence of an argon buffer gas, find population of vibrational states up to v = 32. The relative populations have a characteristic temperature of 600 K for v = 0—4 and 3600 K for v = 5—32 with evidence of non-thermal population of v — 13—16. This study also observes population of A n and a 3II states of BaO with v = 0—4. A molecular beam study of Ba + N20 with laser-induced fluorescence detection indicates that the BaO( X) product is formed with a very high rotational temperature. 

More recently we described the calculation of differential cross sections (DCSs) for the CI+H2 reaction.[35] These were used in the interpretation of ongoing crossed molecular beam studies. The rationale for this investigation is that DCSs offer, in principle, a far more detailed probe of the dynamics than the integral cross sections (ICSs). This paper [35] marked the first ever fully quantum mechanical determination of reactive DCSs for a set of coupled ab initio PESs. Because of space constraints, no details of the determination of the DCSs were reported.[35] The goal of the present article is to present, for future reference, these details. 

Garton, D. J.. Minton, T. K., Maiti, B., Troya, D., Schatz, G.C. (2003) A crossed molecular beams study of the O( P) -I- H2 reaction comparison of excitation function with accurate quantum reactive scattering calculations, J. Chem. Phys. 118, pp. 1585-1588. 

In light of previous experimental and theoretical work on the F f H2 reaction, it can be seen why an experisient of this complexity is necessary in order to observe dynamic resonances in this reaction. The energetics for this reaction and its isotopic variants are displayed in Figure 1. Chemical laser (11) and infrared chemiluminescence (12) studies have shown that the HF product vibrational distribution is hi ly inverted, with most of the population in v=2 and v°°3. A previous crossed molecular beam study of the F + D2 reaction showed predominantly back-scattered DF product (13). These observations were combined with the temperature dependence of the rate constants from an early kinetics experiment (14) in the derivation of the semiempirical Muckerman 5 (M5) potential energy surface (15) using classical trajectory methods. Although an ab initio surface has been calculated (16), H5 has been the most widely used surface for the F H2 reaction over the last several years. 

The formation of the complex has, in fact, been verified at 1.43 and 3.25 eV (LAB) of ion kinetic energy by the crossed molecular beam study of Wolfgang and co-workers [103, 140] (see Section 4.4.2). Also we can find some evidence that the complex formed in the reaction of C2H4 + C2H4 is an intimate complex [277—279]. In such cases, the application of the quasiequilibrium theory of unimolecular reactions to the ion-molecule complex would yield information on the distribution of the... 

Futrell J H 1992 Crossed-molecular beam studies of state-to-state reaction dynamics State-Selected and State-to-State lon-Moleoule Reaotlon Dynamlos Part 1. Experiment ed C Ng and M Baer (New York Wiley)... 

From a cross molecular beam study of the displacement of chlorine by a fluorine... 

The results just cited seem to demonstrate that the potentials of the rare gases have the same forms, yet crossed molecular beam studies show that the potentials are not strictly conformal. To put these results into perspective it is useful to make a distinction between utility and validity employed by Hanley and Klein in a discussion of the m—6—8 potential. They define utility as the ability to correlate particular kinds of data and validity as the ability. . . to fit all possible kinds of data and, at the same time, to be compatible with independent fundamental ideas on the nature of the forces between molecules.. The principle of corresponding states has very great utility even if its validity may in some sense be challengeable. 

Qiu M (2006) thesis high resolution crossed molecular beams study on the F - - H2 reaction. In Dalian Institute of Chemical Physics, CAS. Dalian, China... 

Qiu MH, Che L, Ren ZF et al (2005) High resolution time-of-flight spectrometer for crossed molecular beam study of elementary chemical reactions. Rev Sci Instnim 76 083107... 

F + H2 reaction first attracted attention due to the application of chemical laser. This is the first reaction which has product vibrational state resolved measurements. Using chemical laser [20] and infrared light emitting [21, 22], researchers found that the population of the product HF vibrational states is highly inverted. Crossed molecular beam studies of this system are the main work of Yuan Tseh Lee s Nobel Prize in Chemistry in 1986 [12, 13]. In this chapter, studies on resonance phenomenon in the F + H2 reaction are mainly described. In Sect. 3.1, studies on resonance in the F + H2 reaction are reviewed crossed molecular beam studies in the F( P2/3) -I- H2 HF - - H reaction are introduced in Sects. 3.2 and 3.3 discusses the studies of the F( P2/3) -1- HD -> HF + H reaction, and the last section is a summary. 

Crossed molecular beam studies using imaging detection of products have been restricted to the determination of non-state-selective differential cross-sections, in which an atomic product is probed using (1 + 1) REMPI, or in which a molecular product is probed by universal photoionization. This is because molecular beams are normally skimmed and typical product densities per quantum are only of the order lO cm this approaches the sensitivity limit of state-selective REMPI. In addition, with the exception of (1 + 1) REMPI, the probe laser must be focused, thus creating a very small interaction volume that yields extremely low count rates. The reaction F + CU4 (see Liu (2001)) was the first to be studied by (2 + 1) REMPI in a crossed molecular beam experiment to measure state-selected differential cross-sections. The first study of a neutral bimolecular reaction using a crossed-beam arrangement and 1 + 1 REMPI detection of an atomic product was carried out for... 

Farrar JM, Lee YT. 1975. Crossed molecular-beam study of F + CHsF. J. Chem. Phys. 63(8) 3639-3648. 

Crossed Molecular Beam Studies on Atom-Molecule Van der Waals Complexes 399... 

CROSSED MOLECULAR BEAM STUDIES ON ATOM-MOLECULE VAN DER WAALS COMPLEXES... 

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