UV-VIS and IR Spectroscopy introduction

Question 1

What do these three of spectroscopys helps to identify and why are they useful in forensic chemistry?

Answer 1

• Determining the identity of an unknown compound is crucial in forensic chemistry
• Applies to samples of all classes, from illicit drugs to those of biological origin, found in an explosive, and so on.
• How many atoms are present in the compound? How are the atoms connected to each other? Are there any single, double, or triple bonds? Does this compound exist in different polymorphic forms, and if so, which specific stereoisomer are we dealing with here? What exact functional groups are present in the molecule?
• Determine the presence (and absence) of functional groups through a spectroscopic characterization tool, known as infrared spectroscopy.

Question 2

The electromagnetic spectrumis behind the basis of spectroscopy, what is the wavelength of the visible region and what are some common uses of the spectrum?

Answer 2

• Likely already familiar with the visible region (~400-750nm), but only one region!
• Common uses of:
  ** X-ray –** medical imaging
  ** Ultra-violet – tanning/nail lamps
  ** Infrared – heat lamps
  ** Microwave – kitchen appliance
  ** Radio – communication

Question 3

In most spectroscopy, what is seen as the physical stimulus?

What is the mass component?

Answer 3

The electromagentic energy sources

The energy sources from the EM spectrum are pure energy, so therefore have **no detectable mass component **
* consider alpha rays: this type of energy consists of helium, which therefore has a detectable mass, so can’t classify alpha rays as being on the electromagnetic spectrum (since not an EM type of energy)

Question 4

Spectroscopy is a technique used for what?

Answer 4

• Spectroscopy is a technique used to analyse and quantify the changes in energy states of a given molecule
• Particularly for analytical and organic chemistry, interested in quantifying the energy associated with the vibration of a bond, transition to a particular electronic energy level, etc.

Question 5

What do absorption of energy cause and how is this often represented?

Answer 5

• Absorption of energy causes an atom or molecule to go from the ground state (initial) to a higher energy state (excited state), often represented by an energy level diagram: