On hyperfine frequency shifts caused by buffer gases: Application to the optically pumped passive rubidium frequency standard

Experiments are reported on the effect of buffer gases on the hyperfine frequency of rubidium 87 as used in passive rubidium frequency standards. In some mixtures of buffer gases a strong quadratic dependence of the frequency on temperature is observed. The data are explained by means of a phenomenological approach and with the help of data published previously on pure buffer gases. A comment is made on an article which appears to lead to doubtful conclusions.