A quantitative study was made of the variation with vapor pressure of the diffusely scattered (absorbed and re-emitted) radiation from mercury vapor and of the regular reflection from a quartz-mercury vapor surface (specular reflection) which had been observed by Wood. The mercury vapor was contained in a quartz cell, and the intensity measurements were made with a photo-cell, with a stabilized low pressure discharge tube used as a source.

Both scattering and specular reflection were present over the range of vapor densities corresponding approximately to the range of condensed mercury temperatures between 100°C and 300°C. The scattered radiation increased up to 50°C and then fell off rapidly and was less than 0.5 percent at 300°C. Specular reflection was less than 0.5 percent below 100°C, and was measurable at 125°C, at which temperature the product of the cube root of the number of atoms per cubic centimeter and the wave-length was approximately seven. Over the range of densities corresponding to the range 150°C to 300°C, most of the energy of the 2537A radiation incident upon the mercury vapor was dissipated in the vapor.

The a.c. method, previously used in this laboratory for measurement of mean lifetimes, was used to study the persistence of the radiation in the quartz cell. For vapor pressures above 75°C there was no apparent change in the form of the curve giving the relation between the emission by the cell of scattered radiation and the elapsed time. Within the resolution of the timing method, about 1/40 of the lifetime of the excited state, the specular reflection showed no delay.

The optical constants, index of refraction and coefficient of absorption, of dense mercury vapor for the 2537A line were calculated from the reflectivity at two different angles of incidence. Their ratio remained nearly constant as the vapor pressure increased.

• Received 28 April 1947

DOI:https://doi.org/10.1103/PhysRev.72.332