EXPERIMENTAL-DETERMINATION OF THE DISPERSION IN THE MEAN LINEAR DIPOLE POLARIZABILITY ALPHA(OMEGA) OF SMALL HYDROCARBONS AND EVALUATION OF CAUCHY MOMENTS BETWEEN 325 NM AND 633 NM

The frequency dependent linear mean dipole polarizability alpha(omega) of the hydrocarbons CH4, C2H6, C3H8, n - C4H10, C(CH3)4 (neopentane), C2H4, C3H6, and cyclo - C3H6 has been determined by precise measurements of the refractive index in the frequency range between 0.07198116 a.u. (lambda = 632.990 nm) and 0.1401389 a.u. (lambda = 325-130 nm). This is the first experimental determination of alpha(omega) in the UV frequency region of neopentane and cyclopropane. It will be shown, that the uncertainty in the relative dispersion DELATalpha(omega)/DELTAomega of alpha(omega) is mostly determined by the uncertainty in the frequency of the radiation sources used. In addition, Cauchy moments S(-2), S(-4), S(-6), and S(-8) are calculated with an extended numerical procedure from the measured data sets, showing that a simple Gaussian least-squares fit of alpha(omega) in omega2 is not sufficient to obtain S(-2k). In additon, some data of the relative dispersion of the second refractivity virial coefficient of some of these gases are presented.