Corsini et al. measured for the D 1 transition in 85 Rb and 87 Rb hyperfine frequency shifts and spin relaxation times with saturated alkane and mono-unsaturated alkene cell coats. It was assumed that the hyperfine frequency shift is proportional to cell-wall dwell time (and adsorption energy). For 87 Rb with a paraffin and an alkene (C20-24) coat in spherical cells at 21 • C and 28 • C, respectively, hyperfine frequency shifts (and spin relaxation times) of -57 Hz (3.5 s) and -83 Hz (17.7 s) were observed. It was concluded that spin relaxation time depends not on the cell-wall dwelling time but on a smaller RMS magnitude of the average spatial fluctuations of the cell-wall adsorption energy.