Electronic Transitions and Spectroscopy
The term “electronic” connotes electron, and the term “transition” implies transformation. In a molecule, the electrons move from a lower to a higher energy state due to excitation. The two energy states, the ground state and the excited state are the lowest and the highest energy states, respectively. An energy change is observed with this transition, which depicts the various data related to the molecule.
Photoelectron Spectroscopy
Photoelectron spectroscopy (PES) is a part of experimental chemistry. It is a technique used in laboratories that involves projecting intense beams of radiation on a sample element. In response, the element ejects electrons for which the relative energies are measured.
What processes lead to fluorescence and phosphorescence? Which comes at
higher energy? Which is faster?
Introduction-
The branch of chemistry that deals with the study of Photochemical reactions is called Photochemistry.
The reaction which takes place by the absorption of the infrared or visible or ultraviolet radiations is called a photochemical reaction.
The phenomenon of emission of light due to a chemical reaction is called Chemiluminescence. For example- Glowing of yellow phosphorous that is when yellow phosphorous is exposed to air, it is slowly oxidised to P2O5. The P2O5 formed in the excited state; it loses energy and greenish white light is emitted.
Explanation-
The Chemiluminescence is of 2 types – Fluorescence and Phosphorescence
Fluorescence- Certain substances which when are exposed to light or radiations absorbs energy and then immediately starts to reemit the energy in the form of light. Such a process of emission of light almost instantaneously is known as Fluorescence. The substances that emit light are called Fluorescent substances.
Example –
(1) Certain inorganic compounds like Uranyl sulphate (UO2SO4) and Fluorite (CaF2).
(2) Certain organic compounds like Fluorescein and eosin
Phosphorescence – There are certain substances which are most likely to glow even when the external light source is cut off. Such kind of substances are called Phosphorescent substances. This phenomenon of emission of light even after the external light is cut off is known as Phosphorescence.
Phosphorescence is a slow Fluorescence.
Example –
(1) Many dyes when dissolved become phosphorescent.
(2) Zinc sulphide or alkaline earth metal sulphides are phosphorescent.
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