Rep:Mod:qx5117lab2

EX3 Section

BH3

B3LYP/3-21G level

        Item               Value     Threshold  Converged?
Maximum Force            0.000217     0.000450     YES
RMS     Force            0.000105     0.000300     YES
Maximum Displacement     0.000900     0.001800     YES
RMS     Displacement     0.000441     0.001200     YES

B3LYP/6-31G level

E = -26.61532 a.u.

        Item               Value     Threshold  Converged?
Maximum Force            0.000012     0.000450     YES
RMS     Force            0.000008     0.000300     YES
Maximum Displacement     0.000064     0.001800     YES
RMS     Displacement     0.000039     0.001200     YES

 Low frequencies ---  -10.3498   -3.4492   -1.2454   -0.0054    0.4779    3.2165
 Low frequencies --- 1162.9519 1213.1527 1213.1554

BH3 molecule

frequency analysis

Frequency analysis log file: Media:BH3 OPT 631G FREQ QX5117.LOG

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

Q:Why are there less than six peaks in the spectrum, when there are obviously six vibrations?

Because there is a symmetric stretch at 2582 cm-1 with zero intensity, so no peak. And there are two sets of identical vibration at 1213 and 2716 cm-1. For these four vibration, there are only two peaks observed as these are degenerate. In total, there are only three peaks observed at 1163, 1213, 2716 cm-1.

MO of BH3