UV Visible Spectroscopy

Ability to consume maximum energy at a particular wavelength
λmax is inversely propotional to energy
200nm - Maximum energy
800nm - Low energy

Hypsochromic shift / Blue Shift- shifted towards shorter wavelength max energy
Bathochromic shift/ Red shift- shifted towards lomger wavelenght min energy
Hyperchromic Effect- increase in absorption intensity
Hypochromic Effect- Decrease in absorption intensity

s → s Transitions ( σ → σ ) e.g. saturated alkanes

n → s* Transitions e.g non bonding electrons

n → p*
(Sat Aliphatic Ketones

p → p*
(Conjugated Dienes )

• Molar Absorptivity is defined as a measure of a chemical's ability to
absorb light at a specified wavelength.

Chromophore -Any group of atoms that absorbs light whether or not a color is thereby
produced. e.g. C=C, C=O, NO2 etc..,

• An auxochrome is a group of atoms attached to a chromophore which
modifies the ability of that chromophore to absorb light

Beer-Lamberts Law

A = log I0 / It

A= log 1/ T

A= – log T

A = abc

A = εbc

Instrumentation of UV /Visible spectroscopy

Sample containers- cuvettes

Detector- Photo multiplier Tube ,Linear photodiode Array , Charge coupled device

Wavelength selector ( Monochromator)

Signal processor

Source- D2 lamp ,Tunsgten filament lamp

19PH34