Image from page 84 of "The Bell System technical journal" (1922)
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mplitudes and the permitted vibration-energies; whena quantum excites one of these and rebounds with the remainder ofits energy, the energy which it gives up is spent in augmenting thevibrations of the nuclei. These low-energy excited states are responsible for Ramans dis-covery; partly because, as I have stated, they survive when themolecules are jammed together into a liquid—a fact which evidentlymeans that the electrons, which produce the force upon the nuclei CONTEMPORARY ADVANCES IN PHYSICS 77 countervailing their reciprocal repulsion, are shielded from the outerworld, presumably by other electrons lying still farther outward fromthe nuclei; and partly because their energy-values are so convenientlylow. This latter point can best be illustrated with an example.To perceive a relatively feeble optical effect, or one which is expectedto be feeble, it is best to produce it in the visible spectrum—not merelyin order to observe it with the eye; the major reasons are rather, that in
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Fig. 2—At top, spectrum of primary light (mercury arc); below, spectra of lightscattered by benzene, toluene, pentane respectively. (C. V. Raman; Indian Journalof Physics.) going away from the visible spectrum-range in one direction we findthe photographic plates becoming rapidly less sensitive, while in theother direction the transmission of the rays through matter growssteadily worse. Suppose then that one tries to produce the Ramaneffect by light near the high-frequency limit of the visible—say about4000 A., where the quantum-energy is about 3 equivalent volts. If 78 BELL SYSTEM TECHNICAL JOURNAL the scattered quantum in its turn is to be in the visible spectrum, itswave-length must be less than some 8000 A., its energy more thanroughly 1.5 equivalent volts. The primary corpuscle of light musttherefore not cede to the molecule or atom more than (3 — 1.5) or 1.5equivalent volts of energy—the material particle must therefore beable to receive energy in quantities less than th
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