








MP2/6311+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,
ccpVTZ 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 triplezeta bases. 






Following the lead of Demaison et
al., MP2/6311+G(3df,3pd) optimization was made of a number of
molecules containing CC, 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. 







CC 
~ r_{e}(Å) = 0.95172
× r_{opt} + 0.07134 
RSD = 0.0014 Å 





C=C 
~ r_{e}(Å) = 0.96955 × r_{opt}
+ 0.03761 
RSD = 0.0022 Å 





CC triple bond 
~ r_{e}(Å) = 0.75655 × r_{opt}
+ 0.28594 
RSD = 0.0006 Å 





C=O 
~ r_{e}(Å) = 1.06246 × r_{opt}
 0.07921 
RSD = 0.0020 Å 





CF 
~ r_{e}(Å) = 0.97855 × r_{opt}
+ 0.2742 
RSD = 0.0018 Å 





CCl 
~ r_{e}(Å) = 1.00922 × r_{opt}
 0.01189 
RSD = 0.0024 Å 





CBr 
~ r_{e}(Å) = 0.99977 × r_{opt}
+ 0.00400 
RSD = 0.0012 Å 





CN triple bond 
~ r_{e}(Å) = 0.68844 × r_{opt}
+ 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, ~ r_{e}. 










[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 




