Measurements of collision-induced broadening by Faraday rotation

The influence of collisions on magneto-optical rotation spectra is considered. By using a Rydberg state and nearby doubly-excited perturbers of the barium spectrum as probes, it is shown that, for a given spectral resolution, the broadening of the lines as a function of pressure can be determined in a sensitive way at lower pressures of the perturbing gases than in conventional photoabsorption experiments. The relative f-values of the lines (which do not change significantly in the pressure range investigated) are also accurately monitored by the same method. For the 5d8p doubly excited states in Ba and the Rydberg member which lies between them, the f-values are found to be constant to an accuracy of 5% as the pressure of rare gas is increased in the range up to 100 mb. We have also observed an intruder which can only be excited in the presence of the magnetic field. (author)