Irreducible components of the density matrix. Application to optical pumping

The mechanism of fine structure transitions in atom-atom collisions is discussed, within the framework of the molecular representation, in terms of the evolution of the colliding system from one Hund's coupling case to another. Simple models of the process can be constructed. The results are compared in the case of Na(3p)-He collisions with the results of exact calculations. Choosing the molecular potentials given by Nikitin or by Bottcher and taking into account trajectory effects, the calculated cross sections are in close agreement with experiment. The discrepancy with the quantal results of Reid, which is about 20% for the fine structure transition, is primarily due to the use of different potential and to trajectory effects.

https://iopscience.iop.org/article/10.1088/0022-3700/7/16/020/pdf

Use of Hund's coupling scheme in the theory of fine structure transitions in atom-atom collisions: application to Na(3p)-He collisions

This is a report on a new method of measuring cross sections for the collision induced population transfer between single Na — 3p
2
P fine structure Zeeman states. The experiments are done for the five inert gases at the magnetic field strengths of 6, 17, 24, and 51 kOe. From the optically excited2
P
3/2,±3/2 and2
P
1/2,±1/2 states, respectively, the transfer to the other Zeeman states is studied. The method allows the determination of cross sections for which the influence of the magnetic field is cancelled and which render possible the calculation of cross sections for the transfer and the relaxation of all2
P density tensor components of the degreek=1, 2, and 3. The comparison with previous theoretical and experimental results gives satisfactory agreement. As an application the six Grawert parameters are deduced for the inert gases.

Collision induced transitions between Zeeman substates of laser excited sodium atoms in very high magnetic fields

For pt.I see ibid., vol.7, p.1543 (1974). Quantal close-coupling calculations of Na(32Pjmj)-He(1S) collisions are presented. The Baylis (1969) and a combined Baylis-Krauss et al. (1971) potentials are investigated in the temperature range 400K-4500K. The cross sections for population transfer, multipole relaxation and coherence transfer appropriate to gas-phase experiments, and the population transfer cross sections for beam experiments, are opacity analysed and the opacity functions are studied as a function of l. The ranges of l contributing to depolarization and inelastic processes overlap and cross sections are of similar magnitude. Rotation of the internuclear axis is the main transition mechanism and the cross sections can be characterized by the three Grawert parameters.

W.B. Schneider

Papers

Collisional depolarization of excited sodium atoms

The influence of foreign gases on the resonant and sensitized hanle curves in the sodium d lines