Collision lifetimes

Figure 5.19 Collision lifetime in picoseconds from the time delay matrix versus collision energy in kcal/mol. The resonance states are seen to be long lived.

J.L. Kinsey, The density of states for interacting systems with inelastic transitions and its relation to the collision lifetime, Chem. Phys. Lett. 8 (1971) 349. 

The collision lifetime of benzene with Ar increases as the relative kinetic energy of the colliding partners decreases [8]. The long lifetimes of the collision complex at low kinetic energies enable stabilizing termolecular collisions to occur and this fact explains the formation of clusters in low-temperature molecular beams. 

Draeger, J.A. (1985) The methylbenzenes. 1. Vapor-phase vibrational fundamentals, internal rotations and a modified valence force-field, Specwochim. Acta., 41A, 607-627. Bemshtein, V. and Oref, I. (2001) Dependence of collisions lifetimes on translational energy, J. Phys. Chem. A. 105, 3454-3457. 

R. T Pack, E. A. Butcher, and G. A. Parker, Accurate three-dimensional quantum properties and collision lifetimes of the H + 02 combustion reaction,/. Chem. Phys. 102 5998 (1995). 

Finally, in Fig. 6 we present the collision lifetime matrix eigenvalues associated with the resonances in the partial wave occurring just before the opening of... 

Figure 6. Collision lifetime matrix eigenvalues (in atomic units) for the partial wave just below the opening of the n = 4 H-atom channel as a function of energy. One atomic unit of time is the classical time it takes an electron in the H-atom ground state to traverse one radian. The ordinates of the off-scale peaks of the dashed and full curves occurring at 0.93145 Ryd and 0.93713 Ryd are 1.3 X 10 and 1.9 x 10 atomic units respectively. The arrows locate the positions of the resonances.

It is important to realize that the relaxation times might depend on some factors that are properties of the atom or molecule itself and on others that are related to its environment. Thus rotational spectra of gases have linewidths (related to the rotational relaxation times) that depend on the mean times between coUisions for the molecules, which in turn depend on the gas pressure. In liquids, the collision lifetimes are much shorter, and so rotational energy is effectively non-quantized. On the other hand, if the probability of collisions is reduced, as in a molecular beam, we can increase the relaxation time, reduce linewidths, and so improve resolution. Of course, the relaxation time only defines a minimum width of spectral lines, which may be broadened by other experimental factors. 

In their early calculations Hipes and Kuppermann used the finite element method to solve the surface eigenvalue problem at each required value of the hyperradius p. However, like Parker and co-workers, they have since found that other techniques may make their calculations easier to do. Specifically, Cuccaro, Hipes, and Kuppermann have published two papers in which they describe a variational approach to the surface eigenvalue problem [131] and apply it to the calculation of J=0 and J=1 reaction probabilities and collision lifetime matrices for the PK2 and LSTH potential energy surface representations of H-hH2 this work provides the first practical demonstration of the doubled Delves coordinate method for J>0. 

A. Kuppermann and J. A. Kaye, Collision lifetime matrix analysis of the first resonance in the collinear F + H2 reaction and its isotopically substituted analogs, Chem. Phys. Lett, submitted for publication. 

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