Rep:Mod:jc6116 1

BH₃ Molecule

Basis Set

B3LYP/6-31G(d.p.)

Summary Table

Item Table

        Item               Value     Threshold  Converged?
Maximum Force            0.000004     0.000450     YES
RMS     Force            0.000003     0.000300     YES
Maximum Displacement     0.000017     0.001800     YES
RMS     Displacement     0.000011     0.001200     YES

BH3 molecule

Frequency Analysis

Low frequencies ---  -11.6892  -11.6814   -6.5475    0.0011    0.0281    0.4290
Low frequencies --- 1162.9746 1213.1390 1213.1392

Frequency Link

Media:Jc6116_BH3_FRE_6-31G.LOG

Vibrational spectrum of BH3


wavenumber (cm^-1)	Intensity (arbitrary units)	symmetry	IR active?	type
1163	93	A₂^"	yes	out-of-plane bend
1213	14	E'	very slight	bend
1213	14	E'	very slight	bend
2582	0	A₁'	no	symmetric stretch
2716	126	E'	yes	asymmetric stretch
2716	126	E'	yes	asymmetric stretch

There are totally 6 vibration modes, but from the IR spectrum only 3 peaks can be observed, which are 1163.6 cm-1, 1213.6 cm-1, 2713.1 cm-1. Due to the fact that Mode 2 and Mode 3 are degenerate, Mode 5 and Mode 6 are degenerate. In addition, Mode 4 (2580 cm-1) is not shown in the spectrum since all the dipole moments cancelled out with each other hence it's IR inactive.

LACO MO of BH3

Q1. Are there any significant differences between the real and LCAO MOs?

LCAO MOs does not provide an actual description of the molecular orbitals but an optimised and predicted one, forming by each of the AOs, which can be used as reference of the real MOs. As it can be seen from the previous MOs diagram, real MOs have the exact sizes of orbitals, and the shape of orbitals and their overlap are shown clearly.

Q2. What does this say about the accuracy and usefulness of qualitative MO theory?

The accuracy of the qualitative MO is not as high as the real MOs but it is a reliable prediction of the real MO hence is quite useful.

BH3 Molecule