Collisions between atoms and molecules at ordinary temperatures

Abstract

T h e interaction between helium atoms,* It is possible to eTaluate the cross-section Q(Q,) for scattering through angles greater than 8, bl clacsical theory probided that theory is valid for calculating the scattering through angles as small as 8,. This may be made use of in practice by ensuring that deviations through angles less than 8, vi11 not be observed.

Ionization of helium by slow antiproton impact: Total and differential cross sections

“…At high energies above the Massey maximum [27] at ≈ 100 keV we find the closest agreement with the recent TDDFT results of Baxter et al [16] and the CP results of McGovern et al [8] while the TDCC results of refs. [6] and [7] appear to underestimate the SI cross sections.…”

Quenching cross sections for alkali-inert gas collisions

“…This was first suggested in [6] for the K-inert gases and is now being put on solid ground by the calculations performed for Na-Ne [23] : for this system the weak tail below E .... = 60 eV is due to direct transitions between the ~rNa3s and both the a and 7rNa3p orbitals at relatively large internuclear distances. For this mechanism the excitation and therefore also the quenching cross sections should decrease monotonously with decreasing energy: at low energies which are not influenced by curve crossing phenomena the cross sections should behave like [10,[31][32][33].…”

“…This effective way to convert electronic into kinetic energy of the colliding atoms is not available for the alkali-inert gas systems since all more recent calculations of the relevant molecular states, namely those correlating with M(ZP)+R and M(2S) + R, have shown no indications for regions with strong non-adiabatic behavior [4,5]; the potentials of the molecular states resulting from M(2S)+ R and M(zP) + R are running more or less parallel down to less than 3 atomic units having an energy separation of the order 1 eV. The Massey criterion [33] predicts for such cases that quenching processes at such low energies have to be very improbable. Evidence for the nature of the possible quenching mechanisms has come from the study of the inverse process, the collisional excitation in alkali-inert gas collisions, at moderate collision energies [6][7][8]: by studying the threshold behavior of these cross sections one is in principle able to get information on the various mechanisms which can lead to quenching processes.…”

Perspective: Nonadiabatic dynamics theory

“…In fact, the exponent in Eq. (1) is often called the Massey parameter; 20 and serves as a rough indication of nearly adiabatic behavior if it is much greater than unity-large energy splitting (2 ) and low velocityand diabatic (completely nonadiabatic) behavior if it is much less than unity-small splitting, high velocity. In addition, there are cases for which, even though nonadiabatic transition probabilities are small, it is the nonadiabatic pathway that produces the chemical outcome of interest.…”