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Advances in Physical Chemistry
Volume 2011 (2011), Article ID 864714, 14 pages
Research Article

Diffraction Measurements and Equilibrium Parameters

Faculty of Chemistry, Lomonosov Moscow State University, Moscow 119991, Russia

Received 6 June 2011; Accepted 20 September 2011

Academic Editor: Jan Skov Pedersen

Copyright © 2011 Victor A. Sipachev. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Structural studies are largely performed without taking into account vibrational effects or with incorrectly taking them into account. The paper presents a first-order perturbation theory analysis of the problem. It is shown that vibrational effects introduce errors on the order of 0.02 Å or larger (sometimes, up to 0.1-0.2 Å) into the results of diffraction measurements. Methods for calculating the mean rotational constants, mean-square vibrational amplitudes, vibrational corrections to internuclear distances, and asymmetry parameters are described. Problems related to low-frequency motions, including torsional motions that transform into free rotation at low excitation levels, are discussed. The algorithms described are implemented in the program available from the author (free).