Rotational excitations

In association reactions stabilized by a third body, the third body is often a neutral partner which simply removes excess energy or angular momentum. Hence associations of this type are also unlikely to produce excess rotational 

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Duncan M A, Bierbaum V M, Ellison G B and Leone S R 1983 Laser-induced fluorescence studies of ion collisional excitation in a drift field rotational excitation of N in He J. Chem. Phys. 79 5448-56... 

The strong dependence of the PES on molecular orientation also leads to strong coupling between rotational states, and hence rotational excitation/de-excitation in the scattering. This has been observed experimentally for H2 scattering from Cu surfaces. Recent work has shown that for H2 the changes m rotational state occur almost exclusively when the molecular bond is extended, that is, longer than the gas-phase equilibrium value [ ]. 

Faubel M 1983 Vibrational and rotational excitation in molecular collisions Adv. Atom. Mol. Phys. 19 345... 

Seideman T 1995 Rotational excitation and molecular alignment in intense laser fields J. Chem. Phys. 103 7887-96... 

C3.3.4.2 VELOCITY PROFILES FOR TRANSLATIONAL-ROTATIONAL EXCITATION OF THE BATH... 

Figure C3.3.9. A typical trajectory for a hard collision between a hot donor molecule and a CO2 bath molecule in which the CO 2 becomes translationally and rotationally excited.

Michaels C A, Lin Z, Mullin A S, Tapalian H C and Flynn G W 1997 Translational and rotational excitation of the C02(00°0) vibrationless state in the collisional quenching of highly vibrationally excited perfluorobenzene evidence for impulsive collisions accompanied by large energy transfers J. Chem. Phys. 106 7055-71... 

The use of molecular and atomic beams is especially useful in studying chemiluminescence because the results of single molecular interactions can be observed without the complications that arise from preceding or subsequent energy-transfer coUisions. Such techniques permit determination of active vibrational states in reactants, the population distributions of electronic, vibrational, and rotational excited products, energy thresholds, reaction probabihties, and scattering angles of the products (181). 

Dickinson A. S., Richards D. A semiclassical study of the body-fixed approximation for rotational excitation in atom-molecule collisions, J. Phys. B 10, 323-43 (1977). 

Molecular beams provide the answer. We first met molecular beams in Box 4.1, where we saw how a velocity selector is constructed. A molecular beam consists of a stream of molecules moving in the same direction with the same speed. A beam may be directed at a gaseous sample or into the path of a second beam, consisting of molecules of a second reactant. The molecules may react when the beams collide the experimenters can then detect the products of the collision and the direction at which the products emerge from the collision. They also use spectroscopic techniques to determine the vibrational and rotational excitation of the products. 

Figure 3 demonstrates the simplifications in the spectrum of an optimized laser pulse that can be achieved through the application of the sifting technique [see Fq. (7)]. The excitation efficiency of the pulse is only minimally reduced due to the additional restrictions imposed in the sifting procedure. The example used in this case is for a vibrational-rotational excitation process, H2(v = 0,7 = 0) H2(v =1,/ = 2). 

Figure 2 (a) The optimized electric field as a function of time for the H2(v = 0,) = 0) — H2 (v = 0,7 = 2) rotational excitation process, (b) Absolute value of the Fourier transform of the optimized electric field, (c) The change in populations of the ground-and target excited-state shown as a function of time. Taken from Ref [24] with permission from Qinghua Ren, Gabriel G. Balint-Kurti, Frederick R. Manby, Maxim Artamonov, Tak-San Ho, and Herschel Rabitz, 7. Chem. Phys. 124, 014111 (2006). Copyright 2006, American Institute of Physics. 

For a useful separation of pathways, the variation in final state distributions within each pathway must be at least somewhat smaller than the variation between pathways. The aforementioned dissociation of H2CO provides a perfect example of this technique, in which the H2 produced through the three-center ehmination leads to extensive rotational excitation of CO, with only moderate vibrational excitation of H2. By contrast, the competing pathway involving roaming of one H atom leaves much less energy in CO rotation, with very significant vibrational excitation of H2 [8]. 

The influence of intermolecular bending excitation of the Ne IC1(B, v = 2) complex [97] and of intermolecular bending and rotational excitation of the Ne Cl2(fi, v = 11) complex [112] has been considered theoretically. To date, however, there are no complimentary experimental results reported to complement the predictions. The observation of the linear features in the excitation spectra of Rg XY complexes enables dynamics to be investigated over broader regions of the excited state PES. Thus far, we have investigated the VP of He I C1(B, v = 2, 3) dissociation with n >2 [51]. 

A remarkable agreement with experiment had been found for pure rotational excitations (Table 3). The calculated values are systematically a little smaller because the theoretical internuclear distance is slightly larger than the experimental one, i.e. re= 1.490866 A... 

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