Rovibrationally averaged nuclear shielding constants in OCS

The nuclear shielding constants in OCS are studied using ab initio theoreti cal methods and gas-phase NMR measurements. The shielding surfaces are calc ulated and the rovibrational effects and the resulting temperature dependen ce are analyzed. The temperature dependence of C-13 Shielding in the gas ph ase is determined experimentally in the range 278-373 K, C-13 is the single nucleus for which the experimental data for the temperature dependence can be converted to a reference-independent scale, and good agreement of the m easured and calculated ab initio results is observed. For S-33, We discuss a new, more accurate absolute shielding scale. (C) 1998 Academic Press.