Spectroscopy Flashcards
Forensic Chemistry
What is spectroscopy?
The absorption and emission of light.
What is electromagnetic radiation?
-Contains bundles of photons which are particles of light and are small particles of energy.
-They have no mass and they can travel at the speed of light.
-Photons are unstable.
What is the equation for EM?
E =h ν
E= Energy of photon
H= Planck’s constant
ν=the frequency in Hertz (cycles per second)
C= speed of light
What is the relationship between wavenumber and energy?
If the wavenumber increases the energy increases.
Directly proportional
What is the relationship between wavelength and energy?
If the wavelength increases, the energy decreases.
Indirectly proportional.
What is frequency?
The number of wavelengths passing through a certain point per second.
What is spectroscopy and name the seven types.
Spectroscopy is when matter emits or absorbs radiation. The types of spectroscopy are:
1. Flame spectroscopy
2. Infrared spectroscopy
3. Plasma spectroscopy
4. Ramen spectroscopy
5. UV/ Vis spectroscopy
6. X-ay spectroscopy
What is UV-Vis spectroscopy?
It is the absorption of visible or UV light by a chemical substance.
It can help in the detection of functional groups.
Energy can be detected visually over the wavelengths of 200nm to 400nm as violet light.
Wavelength range can be between 160-780nm.
Define absorption
- It is the amount of electromagnetic radiation that can be absorbed by a sample.
- The energy absorbed will depend on the concentration of the sample.
- It occurs as a change of vibrational and rotational levels; dependent on the arrangement of atoms, their masses, strength and bond distances.
What is Plank’s constant equation?
E= hf
E= energy
h= Plank’s constant
f= frequency
- Relates the energy of a photon to its frequency.
What is a sigma and Pi bond?
- A sigma bond is a single bond.
- A Pi bond is a double bond.
Which bond is stronger to break a sigma or Pi bond and why?
A sigma bond requires more energy to break so they require a high electronic transition compared to a Pi bond that requires less electronic transition.
Electronic transition is when an electron moves from one energy level to another.
A sigma bond has more overlapping in an electronic orbital compared to a Pi bond, this is why more energy is required to break them.
What are the four types of electronic transition and put them in order from the highest transition energy to the lowest.
- σ – σ*
- π – π*
- n – σ*
- n – π*
Sigma to excited sigma requires the most energy to move from one energy level to another.
Pi to excited pi require the least amount of energy.
What is an excited electron?
It is an electron that gain energy by moving from one energy level to another. An excited electron occupies an energy state that is greater than its ground state and its temporarily. An excited electron is unstable.
What is a spectrophotometer and list the components.
It is a scientific instrument that measure how much light is emitted or absorbed by a chemical compound.
The components in a spectrophotometer are:
- Radiation source
-Filter
- Sample
- Detectors
- Recorder
What is infrared spectroscopy?
Electromagnetic radiation in the infrared range being absorbed by molecules. The purpose of this technique is to identify functional groups in a compounds.
The infrared region of the spectrum is 4000cm- 400 cm-1.
Radiation is absorbed by the molecule due to the changes in the vibrational energy states.
what is the vibrational frequency equation?
v= 1/2 pi (square root= k/m)
v = frequency
K= force constant (measure of bond stiffness)
m= reduced mass ( m1m2/ m1+m2)
Name the types of detectors that are used in infrared spectroscopy?
Thermal transducer- temperature dependent, not suitable for FTIR.
Pyroelectric transducer- suitable for FTIR.
Photoconducting transduce- requires cooling by liquid nitrogen.
Define flame spectroscopy?
Analysing the light that has been emitted from a sample which has been heated in a flame.
Define fluorescence spectroscopy?
When matter absorb energy (photons) and they move into an excited state.
Then energy is emitted and then the sample goes back to its electronic ground state.
Define raman spectroscopy?
It measures how much infrared radiation has been absorbed and it is based on scattering interactions.
Can be performed on and through glass and the compound being analysed must have polarizable bonds.
What does FTIR stand for?
Fourier- transform infrared spectroscopy.
Define FTIR
It is a type of technique that obtains an infrared spectrum of emission, absorption from a sample.
What is the Beer Lamberts law?
The intensity of light passing through a sample.
A= elc
A= absorbance
e= molar extinction coefficient
l= path length
c= concentration of sample
