The pressure dependence of refractivity of polar gases

Abstract

The refractive indices of several gases have been measured at varying pressures in the range 0 to 50 cm. For carbon tetrafluoride, methyl fluoride and methyl chloride the refractivity varies directly with the density within the limits of experimental error. For ammonia and sulphur dioxide the increase of refractivity with pressure is less than would correspond to the increase in density. This may be interpreted in terms of a negative ‘first-order hyperpolarizability' for the polar vapours, whose molecular polarizability is being decreased by the influence of the field due to neighbouring molecular dipoles.