nno and nh3 - montana state university · nno higher pressure. 600 800 1000 1200 0.00 0.05 0.10...
TRANSCRIPT
NNO and NH3
A glowing hot barof metal
Mirror moves back andforth causing each wavelength to interfereat different times
IR light intensity from ALL FREQUENCIES AT ONCEinterfering with each other at a particular time
Interferogram
The Fourier Transform of the interferogram provides the spectrum of the light.
Fourier Transform is the technical term for nothing more than:All the overlap integrals of cos(2πνt) with the interferogram.
The amplitude of the overlap integral for a particular frequency = intensity of light at that frequency
The Interferometer
2.4 miles
0 500 1000 1500 2000 2500 3000 3500 40000.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
H2OStretching
H2OBending
Air only (transmittance)BackgroundThis is what is subtracted
Tran
smitt
ance
Time
CO2CO2 Bending
Transmittance Spectrum of air only from our IR spectrophotometer
Wavenumbers cm-1
0 500 1000 1500 2000 2500 3000 3500 40000.0
0.5
1.0
1.5Air onlyBackgroundThis is what is subtracted
Abso
rban
ce
Wavenumbers
H2OBending
CO2
H2OStretching
CO2 Bending
Absorbance Spectrum of air only from our IR spectrophotometer
N2O and CO2N=N=O O=C=O
How different are these?Is the bonding really the same?
Degenerate
The 3N-5 = 4 normal modes for the linear moleculesNNO and CO2
Ab initio computation of vibrational modes and frequencies
CO2 vs. N2O
OCO vs. NNOBoth have 22 electrons
atomic number of C = 6atomic number of N = 7atomic number of O = 8
Start with OCOTake a proton out of left O and give to C
= NNO
1000 2000 3000
-1
0
1
2
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0
time
0
NNO low pressure
500 1000 1500 2000 2500 3000 3500 4000
0.0
0.2
0.4
Abso
rban
ce
Wavenumbers
NNO higher pressure
600 800 1000 1200
0.00
0.05
0.10
0.15
Abso
rban
ce
Wavenumbers
NNO higher pressure
600 800 1000 1200
0.00
0.05
0.10
0.15
Abso
rban
ce
Wavenumbers
NNO higher pressure
Q branch: ∆J=0 for rotational motionWhy is this so intense and sharp???
Angular momentum must be conserved!The PHOTON has angular momentum = 1 h/2πSo, the molecule must increase or decrease by the
same amount.
d) break down of ∆n = + or – 1 for harmonic oscillator (recall HCl)
so many transitions with almost same ∆EJ’=J”
For a linear molecule like N2O ∆J rotational can be + or – 1 because the angular momentum change can bein the degenerate BENDING VIBRATIONS
Assignments for N2O
700 800 900 1000 1100 1200 130
0.0
0.5
1.0
1.5
2.0
2.5
3.0
NH3
abso
rban
ce
wavenumbers
Tunelling