Gas standards in gas electron diffraction: accurate molecular structures of CO2 and CCl4

Abstract

Equilibrium and vibrationally averaged structures of CO2 have been determined using combination of available experimental rotational constants and high level quantum-chemical calculations. Gas electron diffraction patterns of CO2 and CCl4 have been measured and analyzed. A method for fine control of electron diffraction background smoothness is proposed. The patterns of CO2 were used for calibration of electron wavelength. From the patterns of CCl4, molecular structure has been refined. The determined, in this work, parameters can be recommended as reference values in calibration of gas electron diffraction experiments. For CO2, these values are ra(C=O) = 1.1641 (1), ra(O...O) = 2.3241 (1), l(C=O) = 0.0358 (2), l(O...O) = 0.0473 (4) A, c3(C=O) = 3.12 × 10− 6, c3(O...O) = 2.88 × 10− 6 A3. The values for CCl4 are ra(C-Cl) = 1.7665 (7), ra(Cl...Cl) = 2.8828 (12), l(C-Cl) = 0.0502 (4), l(Cl...Cl) = 0.0721 (3) A, and c3(C-Cl) = 0.0, c3(Cl...Cl) = 0.0 A3.