The electric field gradient tensor and the tensors of the molecular magnetic susceptibility and the molecular electric quadrupole moment in nitric acid: A high-resolution rotational Zeeman effect study

Abstract

High-resolution zero field and Zeeman rotational spectra have been studied for HNO3 and DNO3. The measured values for the 14N nuclear quadrupole coupling constants are χ+ = χbb + χcc = −0.929(6) MHz and χ− = χbb − χcc = −0.789(10) MHz for HNO3 and χ+ = 0.731(6) MHz and χ− = −0.576(10) MHz for DNO3. The measured molecular g values are gaa = −0.1213(3), gbb = −0.1097(2), and gcc = −0.0493(2) for HNO3 and gaa = −0.1271(1), gbb = −0.0970(1), and gcc = −0.0474(1) for DNO3. The two independent components of the magnetic susceptibility anisotropy in units of 10−6 erg G−2 mole−1 are 2ξaa − ξbb − ξcc = −0.4(4) and 2ξbb − ξcc − ξaa = +7.9(4) for HNO3 and 2ξaa − ξbb − ξcc = +1.2(3) and 2ξbb − ξcc − ξaa = +6.2(3) for DNO3, where a, b, and c denote the molecular principal inertia axes. From these values and from the known relative position and orientation of the principal inertia axes systems of the two isotopomers, the complete tensors of the molecular magnetic susceptibility, the molecular electric quadrupole moment, and the intramolecular electric field gradient at the 14N nucleus are calculated. The latter is compared to recent ab initio results. The large discrepancies between the two data sets can be reduced, if the SCF-value for the electronic contribution to the intramolecular electric field gradient is appropriately scaled.