Molecular inertia spectroscopic effects

We will assume the mesophase director to be parallel to the direction of the static magnetic field. In the last section, III.E, the no-inertia assumption will be rejected and the diffusion operator (2.6) replaced with the complete Hubbard operator. We shall investigate the spectroscopic effects of molecular inertia in the case of an axially symmetric g-tensor. 

In this section we treat the problem of evaluating an orientational correlational function without the inertial approximation (which assumes the molecular velocity relaxed to thermal equilibrium) and determining the spectroscopic effects of molecular inertia on a spin system S = 2 whose Hamiltonian is described by an axially anisotropic Zeeman interaction. 

Note that the use of the operator of Eq. (3.68) instead of the diffusional limit 3.7, which allows us to evaluate the spectroscopic effects due to molecular inertia, shows the emergence of strong correlation effects when the dif-... 

While the tg structure represents the most well-defined molecular geometry, it is not, unfortunately, one that exists in nature. Real molecules exist in the quantum states of the 3N-6 (or 5) vibrational states with quantum numbers (vj, V2.-..V3N-6 (or 5)). Vj = 0, 1, 2,. Even in the lowest (ground) (0,0...0) vibrational state, the N atoms of the molecule undergo their zero point vibrational motions, oscillating about the equilibrium positions defined by the B-O potential energy surface. It is necessary then to speak of some type of average or effective structures, and to account for the vibrational motions, which vary with vibrational state and isotopic composition. In spectroscopy, a molecule s structural information is carried most straightforwardly by its molecular moments of inertia (or their inverses, the rotational constants), which are determined hy analysis of the pure rotational spectrum or fire resolved rotational structure of vibration-rotation bonds. Thus, the spectroscopic determination of molecular structure boils down to how one uses the rotational constants of a molecule... 

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