INTERFEROMETRIC DETERMINATION OF MEAN POLARIZABILITIES AND 2ND DENSITY VIRIAL-COEFFICIENTS OF METHANE BETWEEN 128-K AND 890-K

Mean dynamic dipole polarizabilities alpha-0(lambda, T) and second thermodynamic virial coefficients B(T) of methane have been determined for the first time in the extended temperature range 128 K less-than-or-equal-to T less-than-or-equal-to 890 K by means of only one apparatus using interferometric low-pressure measurements (p less-than-or-equal-to 0.3 MPa) of the refractive index n(lambda, T, p) in the visible wavelength range (lambda = vacuum wavelength). alpha-0(lambda, T) is in good accordance with previously measured values, but an obvious small minimum at the critical temperature T(c) seems to occur. The B(T)-data determined in the low-temperature range DELTA-T(I) (128 K less-than-or-equal-to T less-than-or-equal-to 298 K) are in fair agreement with other published data. The high-temperature B(T)-values of the range DELTA-T(II) (760 K less-than-or-equal-to T less-than-or-equal-to 890 K) have been measured for the first time. They are in good accordance with extrapolated low-temperature virial coefficients. The mean standard deviation \DELTA-B\ almost-equal-to 8 cm3 mol-1 of the measured B(T)-values may be further reduced by means of more precise measurements of pressure p.