Penning ionization collisional

According to the theoretical investigations by Nakamura [126-128] and Miller [129], the collisional energy dependence of these processes can be calculated if the interaction potential V(R) for the system He(2 S)-M and the autoionization rate r K)jh from the intermediate quasi-molecule [He(2 S)M] to the resulting quasi-molecular ion [HeM] are known. For example, by the classical formula of Miller [129], we have theoretical cross sections for Penning ionization as ... 

The three non-adiabatic effects most easily studied by beam techniques are (1) collisional excitation followed by the emission of radiation for the upper state. (2) collisional ionization to A+ + B-, (3) Penning ionization. Collision induced fluorescence is discussed by V. Kempter in Article 9 the technique is a relatively sensitive one and cross sections down to 10-21 cm2 can be detected, though this still falls short of the sensitivity of bulb spectroscopic methods. The technique is also powerful in that separate cross sections for excitation of members of a multiplet can be obtained although, as always with a beam technique, absolute values are difficult to obtain. 

A classical expression for the cross section for collisional de-excitation of He(2 P) is also derived from the formula by Eq. (16). However, the autoionization widths r(R) for Penning ionization by resonant atoms are not identical to the empirical form of Eq. (18) for electron exchange. Instead, a direct transition due to a dipole-dipole interaction is proposed to govern this Penning ionization [126,139,140,143], that is. 

Quasiresonant Two-Step Excitation and Collisional (Penning) Ionization... 

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