Spin-orbit level inversion

Repeating these experiments using the YAG laser fundamental (1064nm, 1.17 eV), adjusting the energy to achieve the same calculated temperature jump, gave essentially identical (Q, J, A)-state distributions. The inversion of population in the two spin-orbit levels, the population plateau for internal energies below 300 cm and the rapid fall-off of rotational population for... 

The explanation of rule (c) is related to spin-orbit coupling. For an electron in an atom, the energy is lowest when the spin and the orbital magnetic moments are opposed. This implies a low total angular momentum. The inversion of the levels when the shell is more than half full reflects a change of sign of the spin-orbit coupling constant. 

The most probable order of d levels in copper phthalocyanine is illustrated in Fig. 19 (131, 145). The calculated energies (131) are appended. The relative order of the ea and b2g orbitals is the inverse of that found for copper acetylacetonate (238). Although the data for cobalt phthalocyanine (139) cannot be assigned unambiguously, the orbital levels are probably in the same relative order. The hole would then be in the d orbital rather than in the dxt-yt (as in copper phthalocyanine) and this is in accord with the observation that the electron-spin resonance spectrum of cobalt phthalocyanine is solvent dependent, while that of copper phthalocyanine is not (131, 139). The alternative assignment of the cobalt data places the hole in the dxy orbital lying some 16,000 cm-1 above the dxz,dyX pair, which seems unlikely. 

The chemical oxygen-iodine laser operates on an inversion between the 5 P1/2 and 5 P3/2 spin-orbit split states of atomic iodine at a wavelength of 1.315 /xm. A near resonance exists between 02(a A) and I( Pi/2) with an energy difference of only 3.3 kJ/mole, and laser pumping is achieved by collisional energy transfer from the 02(a A) metastable energy reservoir, as shown in Fig. 7. The energy transfer is rapid and a near equilibrium between the upper laser level I( Pi/2) and 02(a A) is quickly established ... 

The inversion operation i which leads to the g/u classification of the electronic states is not a true symmetry operation because it does not commute with the Fermi contact hyperfine Hamiltonian. The operator i acts within the molecule-fixed axis system on electron orbital and vibrational coordinates only. It does not affect electron or nuclear spin coordinates and therefore cannot be used to classify the total wave function of the molecule. Since g and u are not exact labels, it was realised by Bunker and Moss [265] that electric dipole pure rotational transitions were possible in ll], the g/u symmetry breaking (and simultaneous ortho-para mixing) being relatively large for levels very close to the dissociation asymptote. The electric dipole transition moment for the 19,1 19,0 rotational transition in the ground electronic state was calculated... 

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