How is the Dipolar Coupling Hamiltonian Simplified?

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SUMMARY

The dipolar coupling Hamiltonian in quantum mechanics is expressed in the lab frame as H ^D_{ij} = - constants/r_{ij}^3 * I_{iz} * I_{jz} * P_2(cos(θ)). This equation incorporates the internuclear distance (r_{ij}), gyromagnetic ratios (ci and cj), and spin angular momentum operators (I_kz). The simplification to D^{resultant}_{ij} = constants * < P_2(cos(θ(t))/r_{ij}^3> involves averaging the angular portion of the Hamiltonian, represented by the second rank Legendre function, P_2(cos(θ)). This transformation is crucial for understanding dipolar interactions in quantum systems.

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ehrenfest
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Okay, I want to know the answer enough that I will repost the question here:

The dipolar coupling Hamiltonian expressed in the lab frame (units of Hz) is

H ^D_{ij} = - constants/r_{ij}^3 * I_{iz} * I_{jz} * P_2(\cos(\theta))

where r_ij is the internuclear distance between spins, ci and cj are the gyromagnetic ratios of spins i and j, and I_kz are spin angular momentum operators. The angular portion of the
dipolar Hamiltonian is described using the second rank Legendre function, P_2(cos h(t)),
which is a function of the angle h subtending the magnetic field and the ijth internuclear
vector.

Somehow they go from that equation to the following one:

D^{resultant}_{ij} = constants * &lt; P_2(cos(\theta(t))/r_{ij}^3)&gt;
 
Last edited:

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