Vibrational relaxation of hexafluoride compounds: MoF6, ReF6, SeF6, and WF6

Ultrasonic attenuation has been measured in MoF6, ReF6, SeF6, and WF6 at 293 K. In all cases, a single relaxation process was observed and attributed to the total vibrational energy of the relaxing molecule. Isothermal relaxation times were found to be 2.8×10−8, 8.8×10−9, 2.9×10−7, and 2.3×10−8 s atm for MoF6, ReF6, SeF6, and WF6, respectively. Assuming series relaxation, those relaxation times can be converted to the number of collisions required for relaxation Zvib. The values of Zvib vary with the energy of the lowest vibrational mode as expected from the simple Lambert–Salter correlation.