Unit 4 Flashcards
What does resonance mean for atomic absorption
In order to excite the energy must be EXACTLY enough to excite (not above nor below)
Sodium Vapour Lamps
As the lamp heats up, sodium is vaporized and excited in the plasma producing light
What is the energetically favoured excitation
HOMO to LUMO
What are the axes in absorption spectra
Y= absorption X=Wavelength
Why does molecular absorption have wider bandwidth
Its excitation is possible at vibrational and rotational wavelengths as well as electronic
What happens as wavelength increases
As wavelength increases ΔE decreases
What does auxochrome do
Functional group that alters light absorption
What is the triplet state
When the spin switches when excited
Fluorescence vs Phosphorescence
Phosphorescence is when the spin is switched (triplet state) thus its relaxation takes longer (needs to switch back) and light is emitted longer
What is a chromophore
The location on a molecule responsible for electronic transition
The Effect of Conjugation on Chromophores
shifts the absorption maximum to longer wavelengths
What is the consequence of light being absorbed at a higher wavelength
ΔE (the HOMO-LUMO gap) will decrease
Beer-Lambert Law
A=εbC
What is transmitted light
the amount of light that passes through a sample
How to calculate absorbance from transmitted light
A=−log(T) (T as a decimal)
What is the slope in Beers Lambert plot
εb
What would a larger slope on Beers Lambert plot indicate
Higher sensitivity
Why do we measure at max wavelength
Higher sensitivity
What does ε mean
Measure of how strongly a molecule absorbs light
Instrumentation order for spectrophotometer (single beam)
Light, Monochromator, Sample, Detector, Computer
When should Tungsten halogen lamp be used
For visible light
When should Deuterium lamp be used
For UV light
What does Diffraction Grating Monochromators do
Select a particular wavelength of light by utilizing the fact that different wavelengths of diffracted light experience constructive interference at different angles
What do each of terms in a-b=mλ= d(sini +sinr) mean
m=order of diffraction r= angle of diffraction i=angle of incidence d=groove spacing
Czerny-Turner Grating Monochromatic Configuration
slit, mirror, grating, mirror, slit
What m indicates constructive interference
a whole number
What is the benefit and consequence of a more narrow entrance/exit slit
less sensitive (S/N decreases) but better resolution
What is the result of higher groove density
More dispersion
Double monochromator configuration
entrance slit- grating -slit- grating -exit slit
What cuvette do you use for UV
Quartz
Photoelectric effect
Light shone on metal will eject electrons
How does Deuterium Light Work
It excites deuterium and light is released as it relaxes
Benefits of vapour phase
More vibrational and rotational freedom thus finer structure is absorbed
