High temperature vibrational relaxation of H2O by H2O, He, Ar, and N2

The vibrational relaxation of H2O by H2O, He, Ar, and N2 has been studied behind incident shock waves at temperatures between 1800 and 4100°K. The relaxation processes were monitored by the observation of the infrared emission of the water vapor at 6.3 μ (the bending mode) and 2.7 μ (the asymmetric mode). The relaxation times for the two modes were found to be essentially the same with little temperature dependence. This implies rapid intramolecular energy transfer between the various modes. Measured values of pτ are 7.6×10−3, 0.23, 0.49, and 0.69 μsec⋅atm, respectively, for H2O−H2O, H2O−He, H2O−Ar, and H2O−N2 collisions.