DonoghSamu

lab marking

You have a good working wiki. It would be good if you report values of wavenumber in your answers as well. Overall, a good attempt. If you have any specific questions, do email Prof. Hunt

NH3 Molecule

NH3 Optimisation

Key Data Table

Name of Submitted Log File	SD-NH3-OPTIMISATION.LOG
Molecule	NH3
Calculation Method	RB3LYP
Basis Set	6-31G(d,p)
Final Energy	-56.557769
RMS Gradient	1.53e-07
Point Group	C3V
N-H Bond Length	1.02Å
H-N-H Bond Angle	106°

Item Table

Optimised Molecule Image

NH3 Rotatable Image

Vibrational Analysis

Vibrations Table

Mode	Frequency (cm^-1)	Intensity	Symmetry
1	1089.37	145.4277	A1
2	1693.93	13.5571	E
3	1693.93	13.5572	E
4	3461.38	1.0593	A1
5	3589.93	0.2699	E
6	3589.93	0.2699	E

Low frequencies --- -5.6864, -3.6131, -3.6124, 0.0017, 0.0048, 0.0162
Low frequencies --- 1089.3674, 1693.9284, 1693.9284

Charge Distribution

Charges Table

Atom	Charge (e)
Hydrogen	0.38
Nitrogen	-1.13

Log File

Media:SD-NH3-OPTIMISATION.LOG

N2F2 Molecule

NH3 Optimisation

Key Data Table

Name of Submitted Log File	SD-N2F2-OPTIMISATIONFR.LOG
Molecule	N2F2
Calculation Method	RB3LYP
Basis Set	6-31G(d,p)
Final Energy	-308.9912
RMS Gradient	0.053599006
Point Group	C3V
N-F Bond Length	1.39Å
N=N Bond Length	1.22Å
N-N-F Bond Angle	114°

Item Table

Optimised Molecule Image

The molecule from the log file does not have bonds between the F and N atoms, what is going on here?

• The length of the F-N bond exceed GaussView's preset length limit for bonds, resulting in the bond not being visualized despite its known existence.

N2F2 Rotatable Image

Vibrational Analysis

Vibrations Table

Mode	Frequency (cm^-1)	Intensity	Symmetry
1	347.88	0.6108	A1
2	561.25	0.0000	A2
3	771.61	74.7044	B2
4	949.45	75.4125	A1
5	987.25	81.1265	B2
6	1636.61	20.5391	A1

Low frequencies --- -0.0013, 0.0009, 0.0010, 3.2233, 4.3533, 5.0998
Low frequencies --- 347.8772, 561.2472, 771.6105

How many vibrations are expected from the 3N-6 rule?

• N2F2 has 4 atoms, therefore n = 4
• 3(4)-6
• 12-6
• 6 expected vibrations.

Why are there only 4 peaks in the IR spectrum?

• Two vibrational modes have intensities at or very close to zero;
• Mode 1 has an intensity of 0.6108
• Mode 2 has an intensity of 0.0000
• Therefore, neither are strong enough to show up on the IR spectrum.

Which vibration is the asymmetric N-F stretch?

• Vibration mode 3 shows an asymmetric stretch between the Nitrogen and Fluorine atoms.

What is the nature of the highest energy vibration?

• The highest energy vibration is mode 6.
• The nature of this vibration is a N=N stretch.
• This is the highest energy vibration due to the relative strength of the N=N double bond requiring more energy to stretch then for the relatively weaker N-F single bond.

Charge Distribution

Charges Table

Atom	Charge (e)
Fluorine	-0.22
Nitrogen	0.22

Molecular Orbitals

Which MOs are core orbital MOs?

• MO's 1, 2, 3, and 4 are the core orbital MO's of the N2F2 molecule.
• These MO's contain the four different phase combinations of the 1s atomic orbital on each atom in N2F2.

Provide a picture of MO 9 and beside it draw the LCAO diagram

Log File

Media:SD-N2F2-OPTIMISATIONFR.LOG