Liu-Siegbahn-Truhlar-Horowitz

Neuhauser D, Baer M, Judson R S and Kouri D J 1989 Time-dependent three-dimensional body frame quantal wavepacket treatment of the atomic hydrogen + molecular hydrogen exchange reaction on the Liu-Siegbahn-Truhlar-Horowitz (LSTH) surfaced. Chem. Phys. 90 5882... 

The first and second columns of the Tables give the reaction and potential energy surface used. Standard abbreviations are employed for the names of the potential surfaces. Thus. PK = Porter-Karplus potential surface No 2 for H+H2. LSTH = Liu-Siegbahn-Truhlar-Horowitz potential surface for H+Hg. YLL = Yates-Lester-LIu potential surface for H+Hp. LEPS = extended London-Eyring-Polanyi-Sato potential surface and DIM = diatomics-in-molecules potential surface. 

This required between four and six vibrational basis functions, (c) The third group, Walker et al. [109], reported results on the PK PES [125] and the Liu-Siegbahn-Truhlar-Horowitz (LSTH) [127, 126] PES. Further information on these historical implementations are given by Wyatt [4]. References to new calculations on improved surfaces will be presented in the next chapter of this volume. 

Figure 1.1 Contour plot of the Liu-Siegbahn-Truhlar-Horowitz potential energy surface for the H+H2 reaction. The coordinate R is the reactant scattering coordinate, and r is the reactant vibrational coordinate. The portion for large R is the reactant entrance valley, the portion with both R and r small is the reaction barrier region, and the portion for large r is the product exit valley. We note that the scattering and vibrational coordinates approximately exchange roles upon reaction. This strong coupling presents difficulty to otherwise useful quantum mechanical methods.

We present the results of the calculation of the cumulative reaction probability for coUineaj H-f-H2 over the total energy range of 0.37 to 1.27 eV, using the method described above. The availability of accurate PES s and dynamics calculations makes it a good benchmark system to use to study a new method. We use the Liu-Siegbahn-Truhlar-Horowitz [100, 101] (LSTH) PES for the calculations. The coordinates used for the calculations were the mass-weighted rectilinear normal modes [56, 102] referenced to the transition state on the LSTH PES. We denote the two dimensional coordinates by q = (x y) where x is the reaction coordinate and y is the perpendicular vibrational coordinate, i.e. the anti-symmetric and symmetric stretch, respectively. 

Although there have been very many accurate theoretical studies of H + H2, relatively few have used the accurate Liu-Siegbahn (LS) surface as parameterized by Truhlar and Horowitz and... 

H. R. Mayne and J. P. Toennies, Quasiclassical cross sections for the H + H2(0,0) -> H + H2 reaction. Comparison of the Siegbahn-Liu-Truhlar-Horowitz and Porter-Karplus potential surfaces, J. Chem. Phys. 70 5314 (1979). 

Truhlar D G and Horowitz C J 1978 Functional representation of Liu and Siegbahn s accurate ab initio potential energy calculations for H + H2 J. Chem. Phys. 68 2466... 

Figure 3.10 Barrier height Eq vs. cos y obtained from ab initio computations of the potential energy of H3. Here y is the "bend angle," defined in the insert. The minimum barrier corresponds to the collinear attack, indicated by the arrow at Eo = 0.425 eV [ab initio computations by P. Siegbahn and B. Liu, J. Chem. Phys. 68, 2457 (1978) parametrized surface by D. J. Truhlar and C. J. Horowitz, J. Chem. Phys. 68, 2466 (1978), 71,1514 (1979) adapted from R. D. Levine and R. B. Bernstein, Chem. Phys. Lett. 105, 467 (1984)]. Note that the H + D2 collision occurs on the same potential as that of H + H2. Only the masses are different.

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