Gas-dynamic study of pulsed desorption flows into a vacuum

The one-dimensional adiabatic expansion of gas desorbing into a vacuum is studied. The gas is assumed to desorb thermally during a finite period of time from a plane surface. Both the boundary conditions of particle reflection at the surface and sticking at the surface (recondensation) are treated. The general solution of the space- and time-dependent flow field is presented for arbitrary adiabatic coefficient γ. Explicit results are derived and discussed for the case of a monoatomic gas (γ=5/3) and a diatomic gas (γ=7/5 and γ=9/7). The cases of a gas with a large number of degrees of freedom (γ=1), and of γ=3 as a particularly transparent example of the analysis, are treated separately.