Long-range potential capture models

At low temperature the classical approximation fails, but a quantum generalization of the long-range-force-law collision theories has been provided by Clary (1984,1985,1990). His capture-rate approximation (called adiabatic capture centrifugal sudden approximation or ACCSA) is closely related to the statistical adiabatic channel model of Quack and Troe (1975). Both theories calculate the capture rate from vibrationally and rotationally adiabatic potentials, but these are obtained by interpolation in the earlier work (Quack and Troe 1975) and by quantum mechanical sudden approximations in the later work (Clary 1984, 1985). 

ABSTRACT. Calculation of the rate constant at several temperatures for the reaction +(2p) HCl X are presented. A quantum mechanical dynamical treatment of ion-dipole reactions which combines a rotationally adiabatic capture and centrifugal sudden approximation is used to obtain rotational state-selective cross sections and rate constants. Ah initio SCF (TZ2P) methods are employed to obtain the long- and short-range electronic potential energy surfaces. This study indicates the necessity to incorporate the multi-surface nature of open-shell systems. The spin-orbit interactions are treated within a semiquantitative model. Results fare better than previous calculations which used only classical electrostatic forces, and are in good agreement with CRESU and SIFT measurements at 27, 68, and 300 K. ... 

In spite of the wealth of information they provide, global search algorithms ordinarily fail to identify aU the minima of a given cluster. The best explored potential surface for clusters belong to possibly the simplest empirical potential, namely, the Lennard-Jones potential. The Lennard-Jones potential is a simple model that captures the long- and short-range behavior of atoms and molecules. It was proposed in 1931 by J. E. Lennard-Jones (1931) and has been used in innumerable studies ever since. It has the following simple form... 

---