Quasiclassical trajectory distribution

The conclusion that highly vibrationally excited H2 correlated with low-7 CO represents a new mechanistic pathway, and the elucidation of that pathway, is greatly facilitated by comparison with quasiclassical trajectory calculations of Bowman and co-workers [8, 53] performed on a PES fit to high level electronic structure calculations [54]. The correlated H2 / CO state distributions from these trajectories, shown as the dashed lines in Fig. 8, show reasonably good agreement with the data. Analysis of the trajectories confirms that the H2(v = 0—4) population represents dissociation over the skewed transition state, as expected. 

The phenomenon of such bimodal lifetime distribution proposed for reaction 1 on the basis of direct quasiclassical trajectory calculations were tested experimentally with the reaction of diaza-[2.2.1]bicycloheptane to [2.1. Ojbicyclopentane [Equation (2)].6 8 Experimental study on reaction 2 showed that the exo isomer 5x is formed favorably over the endo isomer 5n by about 3 1 in the gas phase. One explanation for the preferential formation of 5x invokes a competitive concerted and stepwise mechanism the concerted pathway directly from 4 to 5 gives 5x with the inversion of configuration at the carbon from which N2 is departing, whereas the stepwise pathway goes through the radical intermediate and leads to both 5x and 5n in equal amount. Alternatively, the product stereochemistry can be rationalized by dynamic matching between the entrance channel to the cyclopentane-1,3-diyl radical intermediate and the exit channel to bicyclo[2.1. Ojpentane as was assumed for reaction 2. 

The stereochemical product distribution of the VCP rearrangement to CP was calculated based on quasiclassical trajectories (VENUS-MOPAQ run on a modified AMI PES parameterized to reproduce ab inito energies (AM1-SRP). Trajectories were initialized at TS1, TS2, and TS3 with quasiclassical TS sampling, in which initial coordinates and momenta that approximated a quantum mechanical Boltzmann distribution were generated by the TS normal-mode sampling procedure. 

Quasiclassical trajectory calculation of the cross-sections for the possible dissociation channels and product energy distributions for ionization/dissociation of ArHj... 

Figure 7. Reaction cross sections for O + H2(v = 0, j) as function of j. (o, ), ( , ), and (A, A) correspond to collision energies Etrjns = 20. 15 and 12 kcal/mol respectively. Open symbols quasiclassical trajectory results [64], full symbols results of the kinematic mass model calculations. Effect of reagent rotation on the distribution of collisions at the barrier is neglected in (a) it is taken into account in (b)[61j.

Rovibrational distributions of HF in the photodissociation of vinyl fluoride at 193 nm A direct MP2 quasiclassical trajectory study95... 

Figure 12 compares the VADW vibrational distribution for H+F2(v=0. j=0) at Etr = 0.106 eV with thermal quasiclassical trajectory... 

Figure 18 shows the VADW rotational distribution for 0( P) reacting with the tertiary hydrocarbon HC(CH3)3 s Isobutane Into v =l at Etr 22.2 kJ mor (Clary et al. (271). The VADW result is compared with experimental measurements (Andresen and Luntz (21) and with quasiclassical trajectory computations (Luntz and Andresen (561). The... 

Another valuable use of accurate quantum dynamics calculations is testing the validity of classical simulations for predicting product-state distributions, and reduced-dimensionality studies of this issue are available for both Cl + H2 [67] and H + CI2 [104], In the present case extensive quasiclassical trajectory (( CT) calculations have been carried out for the full-dimensional Cl + D2 reaction by Aoiz and Bahares [105]. An example of how the QCT results compare to the accurate quantum ones is given in Fig. 4, which shows differential cross sections for Cl + D2(v=0J=1) —> DCl(v ) + D, where v and v are initial and final vibrational quantum number, respectively, j is initial rotational quantum number, and the results are summed over final rotational quantum number j. The comparison in Fig. 4 is for an initial relative translational energy of 10.1 kcal. The agreement is quite good. Notice, however, that the QCT method overestimates the amount of vibrationally excited product. 

Bradley KS, Schatz GC (1997) A quasiclassical trajectory study of H + CO2 angular and translational distributions and OH angular momentum alignment. J Chem Phys 106 8464... 

Troya D, Lakin MJ, Schatz GC, Harding LB, Gonzalez M (2002) Quasiclassical trajectory study of energy and angular distributions for the H + CO2 — OH + CO reaction. J Phys Chem B 106 8148... 

A QUASICLASSICAL TRAJECTORY STUDY OF PRODUCT ROTATIONAL, ANGULAR, AND PROJECTION DISTRIBUTIONS IN THE OH + H2 H2O + H REACTION... 

An assumed model potential surface and the energy disposal observations can be related via comparison of classical (or quasiclassical) trajectory results to the experimentally measured product state distributions. In the latter part of this review the energy disposal calculated from model potential surfaces designed to simulate a given, well-studied reaction is discussed and compared to the experimental distributions. The classical or quasiclassical trajectory calculations become much more difficult for cases having more than three or four atoms, and the use of approximate models, empirical analogies, and chemical intuition becomes necessary. For such situations the information theoretic analysis developed by Levine and Bernstein is particularly valuable and will be used in this review. 

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