Studies of Surface Deactivation of Vibrationally-Excited Homonuclear Molecules in Gaseous Discharge Media Using Coherent Anti-Stokes Raman Spectroscopy (CARS)

摘要

Deactivation coefficients, Gamma(v), of vibrationally-excited on alloys of aluminum, stainless steel alloys, a titanium alloy, gold, Pyrex glass and Teflon were determined from measurements of the wall deactivation rate, k(v), for the v = 1 to 4 or 5 hot bands using coherent anti-Stokes Raman spectroscopy (CARS). A water-cooled positive column discharge was used to populate the vibrational states. The nitrogen gas flow rate was adjusted to optimize the observed decay of the populations. The excited gas was exposed to the tubular specimen surface for precisely controlled residence times and efforts were made to track the influence of surface properties. The Box CARS configuration was used to spatially resolve only the gas that was exposed to the specimen surface. Extensive measurements on Pyrex gave Gamma(1) values between 2.4 x 10 to the -4th power and 6.7 x 10 to the -4th power depending on the treatment history of the surface. The values for Gamma(4) ranged from 2.9 x 10 to the -4 power for the AMS 4943D alloy of titanium to approximately unity for the AMS 312 stainless steel alloy. The low value for titanium can be attributed to the oxide layer. The observed values for gold decreased with increasing temperature consistent with a physical adsorption process. For nearly all specimens, k(v) was proportional to v, or nearly so. Moreover, Gamma(v) values for neat Pyrex, gold foil and aluminum showed similar proportional dependencies on v.