Measurement of "optical" transition probabilities in the silver atom

Abstract

For 22 spectral lines of the silver atom the probability of spontaneous transition has been derived from measurements of the emission intensity of the line and the population of the corresponding upper level. The medium of excitation was the column of a vertical arc discharge in air of atmospheric pressure. The upper electrode (cathode) was a vertical carbon rod; the lower electrode was either a carbon rod filled with a mixture containing silver, or a silver rod. The length of the are was 1 1/2 cm, the current ca. 5 A and the axial field strength ca. 30 V/cm. The spectrum of the arc showed cyanogen bands and silver lines, the intensities of which were measured photographically. The arc temperature was derived from intensity ratios of the CN bands; in most cases the temperature was 5000 to 6000°K. For every exposure the relative populations of the upper levels of the silver lines were derived from the temperature. From these populations and the measured intensities of the silver lines the relative transition probabilities of the lines were calculated. The results are compiled in table I. As the concentration of the silver vapour in the arc is not accurately known, reliable values of the absolute transition probabilities cannot be derived from our measurements; we have confined ourselves to a rough estimation. On the other hand it could be established that in the relative measurements there was no disturbing effect of ionization of the vapour in the arc, nor of self-absorption of the measured silver lines. The transition probabilities of the resonance lines have not been measured.