Rotational relaxation in free jet expansion for N2 from 300 to 1000 K

Publisher Website
Google Scholar
Abstract
The object of this study is to obtain information on the rotation–translation transition probability during N2–N2 collisions. Rotational relaxation for N2 in the free expansion flow is studied by TOF (time-of-flight) measurement with a molecular beam sampling mass filter system. Source temperatures were heated up to 1300 K by an electric heater. The terminal rotational temperatures for various source temperatures and pressures were determined from an energy balance equation in conjunction with the TOF data. Recently, Pritchard et al. have proposed that the transition probability from the ith to the jth rotational states decreases in proportion to some power of the energy difference between the states. This power law was fitted to experimental results for rotational relaxation in the free jet expansion. The results show that the state-to-state rotational relaxation rates vary as the inverse 3/2 power of the energy difference between the initial and final states. The rotational distributions in the jet expansion were also calculated by this power law. The results show a Boltzmann distribution for low j levels but not for high j levels.