Massey parameter

From a quasi-classical point of view, the Massey parameter (1.7) is a... 

The original semiclassical version of the centrifugal sudden approximation (SCS) developed by Strekalov [198, 199] consistently takes into account adiabatic corrections to IOS. Since the orbital angular momentum transfer is supposed to be small, scattering occurs in the collision plane. The body-fixed correspondence principle method (BFCP) [200] was used to write the S-matrix for f — jf xc. At low quantum numbers, when 0)zc —> 0, it reduces to the usual non-adiabatic expression, which is valid for any Though more complicated, this method is the necessary extension of the previous one adapted to account for adiabatic corrections at higher excitation... 

A common result of all the experiments is that most molecules quench the alkali resonance radiation very effectively with total cross sections ranging from 10 A2 to over 200 A2. However, if the molecule BC is replaced by a rare-gas atom, the quenching cross sections become very small at thermal energies. They are probably below 10 2 A2 for quenching by helium, neon, argon, krypton, and xenon.55 The latter result is easily understood in terms of Massey s adiabatic criterion.67 If Ar is a characteristic interaction range, v the impact velocity, and AE the energy difference between initial and final electronic states E(3p) and E(3s), respectively, then we must have a Massey parameter... 

In this expression 8 is the Massey parameter, which depends on the mean thermal velocity v, and AF is the difference in slopes of the initial and final terms at the crossing point. Of course, (2.66) is of typical TST form. It can be generalized to arbitrarily large electronic interactions in a straightforward manner by replacing B with the Zener transmission factor... 

M. Desouter-Lecomte and J. C. Lorquet,/. Chem. Phys., 71,4391 (1979). Nonadiabatic Interactions in Unimolecular Decay. IV. Transition Probability as a Function of the Massey Parameter. 

This model is characterized by the finite value of asymptotic Massey parameter... 

The expression of the E(p(53) demonstrates the signifieant role of the diffraction type nonadiabatie transitions originating from the asymptotic region x oc. The contribution of this region to the amplitude of nonadiabatie transitions is equal to the inverse Massey parameter of Eq.(13) whicii has finite alue at x —> oc because of the asymptotic degeneracy of potential cnergj- curves. 

Ionization in Coiiisions of Heavy Particies Adiabatic Principie and Massey Parameter... 

This relation (Landau Teller, 1936) demonstrates the adiabatic behavior of vibrational relaxation. Usually the Massey parameter at low gas temperatures is high for molecular vibration cox ox k which explains the adiabatic behavior and results in the exponentially slow vibrational energy transfer during the VT relaxation During the adiabatic collision, a molecule has enough time for mai vibrations and the oscillator can actually be considered stractureless, which explains such a low level of energy transfer. An exponentially slow adiabatic VT relaxation and intensive vibrational excitation by electron impact result in the unique role of vibrational excitation in plasma chemistry. Molectrlar vibrations for gases... 

The adiabatic factor y is the Massey parameter for vibrational relaxation transition... 

Rotational-rotational (RR) and rotational-translational (RT) energy transfer processes are usually non-adiabatic and fast, because rotational quanta and, therefore, the Massey parameter are small. As a result, the collision of a rotator with an atom or another rotator can be considered a classical collision accompanied by essential energy transfer. The Parker formula for calculation of number of collisions, Zrot, required for RT relaxation was proposed by Parker (1959) and Bray and Jonkman (1970) ... 

Factors Zrot are low at room temperature values of about 3-10 for most molecules except hydrogen and deuterium, where Zrot is about 200-500 due to high rotational quanta and Massey parameters. RT and RR relaxations are fast processes requiring only several collisions, and their kinetic rates are close to those of thermalization. Rotational degrees of freedom, therefore, are often considered in quasi-equilibrium with translational degrees of freedom and characterized by the same temperature To even in strongly non-equilibrium systems. 

Ionization in Collisions of Heavy Particles. Estimate the adiabatic Massey parameter and ionization probability and cross section for ionization of an Ar atom at rest in collision with an Ar+ ion having kinetic energy twice that of the ionization potential. Compare the ionization probability in this case with the one for the Penning ionization. 

The Golden Rule rests on the assumption of weak electronic coupling. Weak, first of all, means nonadiabatic, that is, the following condition for the Massey parameter J should be fulfilled [298] ... 

Figure 9.25. Time-dependent population of the target diabatic (a) or adiabatic (b) state obtained from exact solution of the Zener problem for two values of the Massey parameter = 0.01 [(a) nonadiabatic crossing] and = 2.25 [(fo) adiabatic crossing]. Time is in units of Tna =...

The above ideas are illustrated in Figure 9.26, where the reaction rate prefactor, /ci2Atst often referred to as the transmission factor, is plotted as a function of coupling V (in terms of the average Massey parameter for different values of the diffusion factor, h = Here = k (0) of Eq. 

---