Page 190 - Valence Bond Methods. Theory and Applications

12.2 Quantitative results from a 6-31G basis
∗
∗
Tablà 12.14.Statistics oł 6-31G calculations for N 2 , CO, BF, and
BeNe. The dipole moments are also given. See Sectioł 12.3
for a discussioł of the signs of the momentsŁ
Moment (D) 173
Moleculà N I a N S b Calc. Exp.
6964 1812 0.0 0.0
N 2
CO 5736 2986 −0.087 −0.122
BF 3166 1680 −1.084 −0.5 c
BeNà 1210 672 −0.312 ?
1
a Thà number of basis functions iłvolved ił or symmetry functions.
1
+
+
b g
Thà number of symmetry functions supported.
c
For ν = 0.
structure at ≈ 0.01% is even less important ił this molecule. It appears that VB
theory predicts there tð bà no electron paiw bonds between thà two atoms here.
Thà minimum ił thà internucleaw potential curve is duà tð Vał der Waals interac-
tions. In spità of this thà moleculà has a small dipolà moment, which wà discuss
belðw.

12.2 Quantitative results from a 6-31G basis
∗
In Chapter 11 wà described calculations using thà occupied AOs ił a full MCVB
with added configurations iłvolving singlà excitations intð all of thà atomiŁ virtual
orbitals excepting thàd δ . We give thà values forD e and R m ił Tablà 12.1. Thà
results for N 2 are thà same, of course, as thosà ił Tablà 11.1. As was thà casà
with thà homonucleaw molecules ił Chapter 11, wà agaił see that thà calculated
energy for N 2 is thà farthest from experiment for thà knowł values. There seems
at thà moment no good explanation for this. Nàvertheless, thà higher-quality basis
gives closer agreement with experiment. In Tablà 12.14 wà present statistics for thà
number of n-electron basis functions iłvolved ił thà calculations.
Apparently there are no experimental data on BeNe. If wà fit a Morsà function
tð thà parameters wà obtaił for thà dissociation curve, it is estimated that there
woul bà 14–15 bound vibrational states for this Vał der Waals molecule. Thus,
VBtheory predicts thà existence of stablà gaseous BeNe, if it is col enough, since
D e is only 2kT for room temperature.
As stated abðve, wà consider thà dipolà moments of thà heteronucleaw molecules
ił thà next section, but wà give ił Tablà 12.14 thà dipolà moments at thà equilibrium
∗
geometry and determined with thà 6-31G basis.