N-15 NUCLEAR MAGNETIC SHIELDING TENSORS IN NITRITE AND NITRATE ION - EXPERIMENTAL AND THEORETICAL DETERMINATIONS

Principal components of the nitrogen shielding tensor are reported for N-15-sodium nitrite and nitrate, determined by magic angle spinning and static N-15 NMR spectroscopy, and compared with values calculated by local origin methods. The inclusion of electron correlation in SOLO (second-order LORG) improves the results significantly for nitrate as well as nitrite ion, and there is further improvement with the inclusion of six surrounding cations for nitrite ion. The changes in the shieldings with change in molecular dimensions indicate that vibrational corrections are significant. The relative magnitudes of the orbital contributions afford insights into the physical origins of the shielding.