Triplet state Positive hole

The first excited state 0i has one node, and this nodal line should be along a straight line electron 1 and position 0 = 180°, This function is antisymmetric with respect to exchange of the electrons (0 —> —0), so this is the (lowest) triplet state. This state will be of low-energy, because it takes care of the Fermi hole, the wave function equal zero for electron 2 at the position of electron 1. 

Positron Annihilation Lifetime Spectroscopy (PALS) provides a measure of free volume holes or voids, free volume, and free volume distribution, at an atomic scale. The technique exploits the fact that the positively charged positron (e" ), the antiparticle to the electron, preferentially samples regions of low positive charge density. When injected in a polymer matrix, thermalized positrons can combine with an electron to form a bound state, known as positronium (Ps). This species can only exist in a void and it rapidly annihilates on contact with the electron cloud of a molecule. For polymer studies using PALS, it is ortho-positronium (oPs, a triplet state) which is of interest. The oPs spin exchanges with electrons of opposite spin on the walls of the cavity and it is annihilated. Thus, the oPs lifetime, 13, gives a measure of the mean free volume cavity radius, whereas the relative intensity of... 

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