Collisionless Intramolecular Vibratonal Relaxation in SF6

Time-resolved spectroscopy is applied to the problem of collisionless intramolecular relaxation within the ground electronic state of polyatomic molecules. The redistribution of vibrational energy within a molecule may be monitored by the different anharmonic shifts which occur when the energy is localized in the different modes. Picosecond infrared-laser-absorption saturation-recovery measurements on S${\mathrm{F}}_6$ show that the relaxation time, for statistical behavior to set in, falls within the limits $1 \mathrm{psec}<T_1<30\mathrm{} \mathrm{psec}$.