Dynamical rules parity rule

Radiative processes and rotational excitation collisions preserve the para or ortho character of the Hj molecule due to the conservation of the total parity of the system (AJ even selection rule). However, at low collision energies, H, (J) collide with in a reactive process which proceeds through the strongly coupled intermediate complex I which leads to a redistribution of the rotational states of Hj without any selection rule on J and induces ortho-para transitions. This is the most simple reactive collision system for which the corresponding electronic potential surface is known (Giese Gentry, 1974). A most dynamically biased (MDB) statistical theory has been developed (Schlier, 1980) which has been tested to be... 

Optical transitions between 4f" levels used for optical pumping and stimulated emission are predominantly of electric-dipole nature. Although f-f transitions are forbidden by Laporte s rule, if the rare earth is located in a non-centrosym-metric site, odd-order terms in the expansion of the static (or dynamic) crystal-field admix states of higher, opposite-parity configurations, such as 4f" 5d, into 4f" and transitions become allowed. The oscillator strengths of transitions between J states are small, 10 . - While ab initio calculations of the probabilities for electric-dipole transitions are not possible, spectral intensities can be treated using the Judd-Ofelt approach discussed below. 

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