Which part of spectrum corresponds to electronic transitions?
Electromagnetic spectrum couples with distinct molecular energy levels. Microwave photons induce rotational transitions, infrared photons drive vibrational stretching and bending, X-rays eject inner core electrons causing ionization. Outer valence electrons from bonding π, nonbonding n to antibonding π*, σ* orbitals require photon energies approximately two to seven electron volts corresponding to wavelength range 200-800 nm, spanning ultraviolet and visible region. Consequently colored biomolecules, conjugated cofactors such as heme, carotenoids, chlorophyll, flavins and aromatic amino acids
Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.
