Interaction of light and matter

In the above rather simplified analysis of the interaction of light and matter, it was assumed that the process involved was the absorption of light due to a transition m - n. However, the same result is obtained for the case of light emission stimulated by the electromagnetic radiation, which is the result of a transition m -> n. Then the Einstein coefficients for absorption and stimulated emission are identical, viz. fiOT< n = m rt. 

Photophysical and photochemical processes result from the interaction of light and matter. When a beam of light passes through matter, several processes can take place as shown in Figure 2.1. 

When electromagnetic radiation interacts with matter it causes the electron density in the material to oscillate at the same frequency as the incident light. Since the interaction of light and matter is a time-resolved process involving many photons, it should not be a surprise that the oscillation produced by... 

Chirality is the origin of the spectroscopic property optical activity. The interaction of light and matter is characterized by the refractive index and the absorption coefficient. For chiral molecules, both the refractive index and the absorbance coefficient of one enantiomer differ for right and left circularly polarized light (r-cpl and 1-cpl). 

Dirac s 1929 comment [227] The underlying physical laws necessary for the mathematical theory for a large part of physics and the whole of chemistry are thus completely known, and the difficulty is only that the exact application of these laws leads to equations much too difficult to be soluble has become a part of the Delphic wisdom of our subject. To this confident statement Richard Feynman [228] added in 1985 a codicil But there was still the problem of the interaction of light and matter , and . .. the theory behind chemistry is quantum electrodynamics . He goes on to say that he is writing of non-covariant quantum electrodynamics, for the interaction of the radiation field with the slow-moving particles in atoms and molecules. 

The interaction of light and matter produces astounding effects and the outcome may be hard to predict. Will light do the desired trick for you A well-trained chemist will have a reliable notion of the reactions that might result from the addition of, say, sodium borohydride to a solution of testosterone but would he or she dare to predict or make an educated guess about what will happen when a solution containing testosterone is irradiated (Scheme 1.1) ... 

We are dealing with the interactions of light and matter. The expression light is used here somewhat loosely to include the near-ultraviolet (UV, 2 = 200 400 nm) and visible regions (VIS, 2 = 400 700 nm) of the entire electromagnetic spectrum (Figure 1.4), which spans over 20 orders of magnitude. 

The mighty and mysterious quantum theory explains the interaction of light and matter in terms of well-defined energy states that characterize an atom or molecule. When the atom or molecule absorbs energy to enter a higher energy state, the energy used is... 

D Fig. 12.1 Most common modes of interaction of light and matter... 

In the early 1900s, scientists conducted two experiments involving interactions of light and matter that could not be explained by the wave theory of light. One experiment involved a phenomenon known as the photoelectric effect. The photoelectric effect refers to the emission of electrons from a metal when light shines on the metal, as illustrated in Figure 1.3. 

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