Molecular Structure of Pyrazinamide: A Critical Assessment of Modern Gas Electron Diffraction Data from Three Laboratories.

Accuracy and precision of molecular parameters determined by modern gas electron diffraction have been investigated. Diffraction patterns of gaseous pyrazinamide have been measured independently in three laboratories, in Bielefeld (Germany), Ivanovo (Russia), and Moscow (Russia). All data sets have been analyzed in equal manner using a highly controlled background elimination procedure and flexible restraints in molecular structure refinement. In detailed examination and comparison of the obtained results we have determined the average experimental precision of 0.004 Å for bond lengths and 0.2° for angles. The corresponding average deviations of the refined parameters from the ae-CCSD(T)/cc-pwCVTZ theoretical values were 0.003 Å and 0.2°. The average precision for refined amplitudes of interatomic vibrations was determined to be 0.005 Å. It is recommended to take into account these values in calculations of total errors for refined parameters of other molecules with comparable complexity.