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Priya Barik posted an Question
November 12, 2020 • 19:04 pm
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30 points
30 points
- IIT JAM
- Chemistry (CY)
Justify or criticise each of the following statements (a) quantum yield of any reaction is always unity. (b) absorption of a photon by the molecule leads always
Justify or criticise each of the following statements (a) Quantum yield of any reaction is always unity. (b) Absorption of a photon by the molecule leads always to a chemical reaction. (c) Delayed fluorescence is phosphoresence. (d) Molar extinction co-efficient is the reciprocal of the thickness of the solution when the intensity of the incident radiation falls to one-tenth of its value.
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(c) Fluorescence and phosphorescence are types of molecular luminescence methods. A molecule of analyte absorbs a photon and excites a species. The emission spectrum can provide qualitative and quantitative analysis. The term fluorescence and phosphorescence are usually referred as photoluminescence because both are alike in excitation brought by absorption of a photon. Fluorescence differs from phosphorescence in that the electronic energy transition that is responsible for fluorescence does not change in electron spin, which results in short-live electrons (<10-5 s) in the excited state of fluorescence. In phosphorescence, there is a change in electron spin, which results in a longer lifetime of the excited state (second to minutes). Fluorescence and phosphorescence occurs at longer wavelength than the excitation radiation.
(a) The quantum yield of photoluminescence is the ratio of the number of the emitted quanta to the number of the absorbed quanta (in the stationary regime). In simple systems, the value of the quantum yield is often considerably higher than unity and is determined mainly by the number of energy levels.
(b) Photochemical Reactions :-These are the reactions that take place by absorption of radiations of suitable wavelength, In such processes, the absorbed light energy is first stored in the molecule and then it is further used to bring about the chemical reaction.