The spin-rotation tensor for H2CO was obtained from very high resolution beam maser measurements of rotational transitions. Spin-rotation tensor elements are Maa= −4.12 ± 0.36 kHz, Mbb= 2.45 ± 0.32 kHz, and Mcc= −2.10 ± 0.34 KHz in the principal axis system. These results are combined with previous molecular orbital calculations of diamagnetic shielding to obtain total absolute shielding tensor elements of σaa= 15.9, σbb= 40.7, and σcc= −1.7 ppm and an average shielding of 18.3 ppm with uncertainties of ±2 ppm or better. A similar analysis is carried out for NH3. Spin-rotation tensors and shielding tensors are given for proton and nitrogen sites with estimated accuracy better than 1 ppm. For NH3σzz(H) = 26.5 ppm and σ(H) = 31.2 ppm. The absolute shielding scale is discussed.
ASJC Scopus subject areas
- Colloid and Surface Chemistry