Compound Analysis

NH₃

Name: Ammonia

Calculation Method: RB3LYP

Basis Set: 6-31G(d,p)

Final Energy E(RB3LYP)= -56.55776873 a.u.

Point Group: C3V

Bond Length= 1.01798 Å

H-N-H Bond Angle= 105.741°

        Item               Value     Threshold  Converged?
 Maximum Force            0.000004     0.000450     YES
 RMS     Force            0.000004     0.000300     YES
 Maximum Displacement     0.000072     0.001800     YES
 RMS     Displacement     0.000035     0.001200     YES

Optimised model of NH3

NH3 optimisation log file

Display Vibrations

None of the frequencies are negative so we have a minimum.

Questions

Using the 3N-6 rule you would expect 6 vibrational modes for NH₃.
Modes 2 and 3 are degenerate and modes 5 and 6 are degenerate.
Modes 1, 2 and 3 are "bending" vibrations. Modes 4,5 and 6 are "stretching" vibrations.
Mode 4 is highly symmetric.
Mode 1 is known as the "umbrella" vibrational mode.
You would expect to see 4 bands in an experimental spectrum of gaseous ammonia.

Charge

The charge on the N atom is -1.125.
The charge on the H atoms is 0.375
You would expect the N to be negatively charged and the H atoms to be positively charged because N is more electronegative than H.

N₂

Name: Nitrogen gas

Calculation Method:RB3LYP

Basis Set: 6-31G(d,p)

Final Energy E(RB3LYP)= -109.52412868 a.u.

Point Group: D∞h

Bond Length= 1.10550 Å

        Item               Value     Threshold  Converged?
 Maximum Force            0.000001     0.000450     YES
 RMS     Force            0.000001     0.000300     YES
 Maximum Displacement     0.000000     0.001800     YES
 RMS     Displacement     0.000000     0.001200     YES

Optimised model of N2

N2 optimisation log file

Display Vibrations

None of the frequencies are negative so we have a minimum.

Charge

The charge on both N atoms is 0.000.

Molecular Orbitals

H₂

Name: Hydrogen Gas

Calculation Method:RB3LYP

Basis Set: 6-31G(d,p)

Final Energy E(RB3LYP)= -1.17853936 a.u.

Point Group: D∞h

Bond Length= 0.74279 Å

         Item               Value     Threshold  Converged?
 Maximum Force            0.000000     0.000450     YES
 RMS     Force            0.000000     0.000300     YES
 Maximum Displacement     0.000000     0.001800     YES
 RMS     Displacement     0.000001     0.001200     YES

Optimised model of H2

H2 optimisation log file

Display Vibrations

None of the frequencies are negative so we have a minimum.

Charge

The charge on both H atoms is 0.000.

Reaction Energies

E(NH3)= -56.55776873 a.u.

2*E(NH3)= -113.11553746 a.u.

E(N2)= -109.52412868 a.u.

E(H2)= -1.17853936 a.u.

3*E(H2)= -3.53561808 a.u.

ΔE=2*E(NH3)-[E(N2)+3*E(H2)]= -0.0557907 a.u.

ΔE=2*E(NH3)-[E(N2)+3*E(H2)]= -146.48 kjmol^-1

The NH₃ product is preferred over the reactants. The product is more stable than the reactants.

SiH₄

Name: Silane

Calculation Method: RB3LYP

Basis Set: 6-31G(d,p)

Final Energy E(RB3LYP)= -291.88802760 a.u.

Point Group: Td

Bond Length= 1.48485 Å

H-Si-H Bond Angle= 109.475°

         Item               Value     Threshold  Converged?
 Maximum Force            0.000000     0.000450     YES
 RMS     Force            0.000000     0.000300     YES
 Maximum Displacement     0.000000     0.001800     YES
 RMS     Displacement     0.000000     0.001200     YES

Optimised model of SiH4

SiH4 optimisation log file

Display Vibrations

None of the frequencies are negative so we have a minimum.

Modes 1, 2 and 3 are degenerate. Modes 4 and 5 are degenerate. Modes 7,8 and 9 are also degenerate.

You would expect to see 3 bands in an experimental spectrum of SiH₄. This is because there are only three unique infrared values in the table.

Charge

The charge on the Si atom is 0.629.
The charge on the H atoms is -0.157.
You would expect the H atoms to be negatively charged and the Si atom to be positively charged because H is more electronegative than Si.

Molecular Orbitals

Mouse over for figure numbers.

Figure 1 has an energy of -5.28056 a.u.
Figure 2 has an energy of -3.63858 a.u.
Figure 3 has an energy of -0.35184 a.u.
Figure 4 has an energy of 0.05053 a.u.
Figure 5 has an energy of 0.22050 a.u.