NMR shielding constants in hydrogen molecule isotopomers
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We analyze the NMR shielding constants in three isotopomers of the hydrogen molecule: H2, HD and D2. The results obtained within the Born–Oppenheimer approximation using the coupled-cluster singles-and-doubles model are very close to the previous theoretical values. In particular, the isotope shifts computed using significantly larger basis sets agree with the earlier literature results, confirming the disagreement of these calculations with the available experimental data. To examine the accuracy of the computed isotope shifts, we analyze in addition the relativistic corrections and estimate the role of the adiabatic and nonadiabatic effects. The relativistic corrections appear to be negligible; on the other hand, the changes in the shielding constants due to the adiabatic and nonadiabatic effects may account for the discrepancies between the computed and experimental isotope shifts.
KeywordsShielding constants Isotope shifts Hydrogen molecule CCSD calculations
We are indebted to Dr Krzysztof Pachucki for many helpful discussions and to Dr Trond Saue for the DIRAC program (GIAO version).
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