Measurements of the Rayleigh depolarization ratios (with and without inclusion of the vibrational Raman contributions), Cotton-Mouton effects and electric field-gradient induced birefringences of gaseous HC≡CH, HC≡CCH 3 and CH 3 C≡CCH 3 at 632.8 nm are analyzed in conjunction with other data to obtain reliable values of the polarizability anisotropies, magnetizability anisotropies and quadrupole moments of these molecules.