Measurements of molecular quadrupole coupling constants

A very accurate and more or less standard procedure for molecular NQCC measurements is rotational spectroscopy where the coupling constants can be determined with great accuracy. Here diatomic 

Casimir s formula (17) applies equally well if is replaced by qj, the specific rotor-dependent EFG. A thorough derivation of all rotor-dependent expressions for the EFG can be found in [64,65] and need 

4 Methodology of relativistic atomic hy-perfine structure calculations 

Before the general methodology of contemporary relativistic EFG calculations is discussed some general aspects are outlined and early four-component hfs calculations are mentioned. 

The results obtained by MBPT serve as a decisive basis for the selection of suitable orbital spaces in high-level ab initio calculations in order to account for the dominant contributions. The MBPT analysis applies equally well to four-component theory where a single configuration wave function built from Slater determinants of Dirac spinors is used as the reference wave function. In the following we will briefly outline the various theoretical approaches for relativistic atomic hfs calculations. 

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