Features/ Accessories: 

• Experiments can be performed with wide range of wavelength 190 nm - 3300 nm (for Liquid samples) 
• Integrating Sphere with a working range of 250 to 2500 nm (for solids) 
• PMT (photomultiplier tube) for the ultraviolet and visible region. 
• PbS detector for near infrared region
• Peltier module for static temperature control with variable stirring speed

Principle:

Typical UV-Vis spectrometers use a deuterium lamp for the UV that produces light from 170–375 nm and a tungsten filament lamp for visible, which produces light from 350–2,500 nm. 

When a photon hits a molecule and is absorbed, the molecule is promoted into a more excited energetic state. UV-visible light has enough energy to promote electrons to a higher electronic state, from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO). The energy difference between the HOMO and the LUMO is called the band gap. Typically, these orbitals are called bonding and anti-bonding. The energy of the photon must exactly match the band gap for the photon to be absorbed. Thus, molecules with different chemical structures have different energy band gaps and different absorption spectra. The most common transitions that fall in the UV-Vis range are π-π* and n- π*. Pi orbitals arise due to double bonds, and n orbitals are for non-bonding electrons. Pi star are anti-bonding pi orbitals. Thus, UV-Vis absorption is by molecules that contain double bonds. Pi orbitals adjacent to each other that are connected, called conjugation, typically increases absorption.  The broad bands or shoulders on the UV-Vis structure is due to the numerous vibrational and rotational states of a molecule, which lead to separate energy band gaps of slightly different energies.  

Absorption follows Beer's Law, A=εbC where ε is the molar Extinction coefficient, b is path length, and C is concentration. The molar Extinction coefficient is the characteristic of an individual compound to absorb at a given wavelength and this property is due to functional groups, conjugation, etc.