VOl. 71
atjo
NOTES The Relation between Magneto-optic Rotation and Refractive Dispersion of Hydrocarbons
organic niolecules, but it is likely to be equal for all hydrocarbons. Equation (2) therefore implies the existence of a linear relation between the oscillator UP A. BONDI strength and the characteristic frequency of the Inspection of data on the magneto-optic rota- “dispersion-electron” of hydrocarbons. As one can observe the constancy of y within tion (Verdet Constant, V ) of hydrocarbonslJ suggested that they may be directly proportional to other families of organic molecules, this relation the refractive dispersion, nvl - nv2 = An. The should hold more widely. The lack of reliable recent extensive and accurate data published by absolute intensity data, particularly in the vacuum Foehr3 make possible the quantitative compari- ultraviolet where the characteristic absorption son which is presented in Table I. It appears that band of the saturated hydrocarbons is located, V / A n is indeed very nearly independent of the precludes a direct test of the postulate made. The hydrocarbon type at low molecular weights and constancy of y in spite of the wide variation in vi substantially constant in the higher molecular (0.S to 2.5 X 1OI6 sec.-l) and in ai encountered in the range of hydrocarbons reported in Table I weight range. The greatest “exaltation” apparently occurs suggests, however, that a relationship at least among the aromatic hydrocarbons, but too few similar to the proposed one exists. (A plot of the measurements are available in this class of com- oscillator strength fl,’ versus V I shows that the pounds to permit any valid generalization. data lie on smoothly ascending curves, which are, As a practical result this observation suggests however, characteristic of each family of (aromathat refractive dispersion and magneto-optic ro- tic) hydrocarbons so tested, and not universal for tation may be used interchangeably. Since refrac- all hydrocarbons as first hoped for.) The utility tive dispersion data are usually more a c c e ~ s i b l e ~ of , ~ Equation (2) for y = const. consists in the posthan Verdet constants, the ingenious scheme of sibility of expressing the refractive dispersion of (magneto-optic) hydrocarbon type analysis pro- hydrocarbons as a function of vi alone, thereby faposed by Foehr3 may now be applied more exten- cilitating the rational treatment of this easily determined physical property. sively. The theoretical background is contained in the TABLE I Hecquerel formula6
REFRACTIVE I ~ I S P E R S I O N ~ OF HYDROCARBONS
COMPARISON UF VERDET CONSTANTO AND
il)
where the universal factor e/21nc.~derives from the Larmor precession, v = frequency of the light used, an/& = refractive dispersion, y = “anomaly” factor. The constancy of the ratio V / An thus means that for hydrocarbons y is a constant. For diamagnetic substances, according to Schutz6 ’.(
*. +‘-b 2 a
2 Avo
if v
