Pressure broadening of UF6 by argon

Pressure broadening of the R(6) manifold in ν₃ of UF₆ at 628.32 cm^?1 has been measured at pressures of 0–30 torr of Ar in a long-path cell at 199 ± 1 K. We obtain a pressure-broadening coefficient of 9.0 ± 1.5 MHz/torr (FWHM), which corresponds to 7.3 ± 1.2 MHz/torr at 300 K. The UF₆-Ar optical collision diameter is 7.4 ± 0.6 Å; this is larger than the hard-sphere kinetic theory collision diameter of 5.2 Å obtained from the diffusion coefficient and implies rapid rotational relaxation.