MP2/6-311+G(3df,3pd) Model for Calculation of Approximate Equilibrium Molecular Structures.
	Accurate calculation of nuclear quadrupole coupling constants in gaseous state molecules requires, of course, accurate molecular structures on which to make the calculation.
	Calculation of near equilibrium molecular structures requires a high level of ab initio theory - for example, CCSD(T) - in conjunction with large bases - for example, cc-pVTZ or larger; which in turn requires computer resources beyond those available for this work.
	However, for calculation of approximate equilibrium structures, Demaison et al. have shown in a series of publications [1 - 8] that errors inherent in more modest quantum chemistry calculation of bond lengths are largely systematic and can be empirically corrected, and that accurate interatomic angles may be obtained at the MP2 level of theory in conjunction with fairly large triple-zeta bases.
	Following the lead of Demaison et al., MP2/6-311+G(3df,3pd) optimization was made of a number of molecules containing C-C, C=C, C=C, C=O, CF, CCl, CBr, and C=N for which equilibrium structures have been reported.  Linear regression analyses of the optimized bond lengths versus the equilibrium bond lengths yield regression equations that may be used for correction of the optimized bond lengths.
	Thus, the following equations have been derived.  Visit the links for more detail.
	C-C ~ re(Å) = 0.95172 × ropt + 0.07134 RSD = 0.0014 Å   C=C ~ re(Å) = 0.96955 × ropt + 0.03761 RSD = 0.0022 Å   CC triple bond ~ re(Å) = 0.75655 × ropt + 0.28594 RSD = 0.0006 Å   C=O ~ re(Å) = 1.06246 × ropt - 0.07921 RSD = 0.0020 Å   CF ~ re(Å) = 0.97855 × ropt + 0.2742 RSD = 0.0018 Å   CCl ~ re(Å) = 1.00922 × ropt - 0.01189 RSD = 0.0024 Å   CBr ~ re(Å) = 0.99977 × ropt + 0.00400 RSD = 0.0012 Å   CN triple bond ~ re(Å) = 0.68844 × ropt + 0.35102 RSD = 0.0007 Å
	The standard deviation of the the residuals (RSD) may be taken as an estimate of the uncertainty in the approximate equilibrium bond length, ~ re.
	[1] J.M.Colmont, D.Priem, P.Dréan, J.Demaison, and J.E.Boggs, J.Mol. Spectrosc. 191,158(1998).
	[2] J.Demaison, G.Wlodarczak, H.Rück, K.H.Wiedenmann, and H.D.Rudolph, J.Mol.Struct. 376,399(1996).
	[3] I.Merke, L.Poteau, G.Wlodarczak, A.Bouddou, and J.Demaison, J.Mol.Spectrosc. 177,232(1996).
	[4] R.M.Villamañan, W.D.Chen, G.Wlodarczak, J.Demaison, A.G.Lesarri, J.C.López, and J.L.Alonso, J.Mol.Spectrosc. 171,223(1995).
	[5] J.Demaison, J.Cosléou, R.Bocquet, and A.G.Lesarri, J.Mol.Spectrosc. 167,400(1994).
	[6] J.Demaison and G.Wlodarczak, Struct.Chem. 5,57(1994).
	[7] M.LeGuennec, J.Demaison, G.Wlodarczak, and C.J.Marsden, J.Mol.Spectrosc. 160,471(1993).
	[8] M.LeGuennec, G.Wlodarczak, J.Burie, and J.Demaison, J.Mol. Spectrosc. 154,305(1992).
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		Last modified: 9 Dec 2009