Elastic velocity-changing collisions have been observed for the first time to our knowledge in a nonpolar molecule by photon-echo studies of SF6 using a frequency-switched CO2 laser that we have developed. The photon-echo decay is nonexponential and reveals the velocity-changing collision cross section to be σvc = 180 Å2, with an average velocity change per collision of Δu = 155 cm/sec. Using delayed optical nutation, we also determine the cross section for the population decay rate (1/T1) to be σpop=335 Å2. To within experimental accuracy, we find that phaseinterrupting collisions are not important (T1≃ T2). A comparison of these cross sections with those for the polar molecule 13CH3F is made.
© 1981 Optical Society of America
B. Comaskey, R. E. Scotti, and R. L. Shoemaker, "Optical coherent transient measurements of velocity-changing collisions in SF6," Opt. Lett. 6, 45-47 (1981)