Abstract
We examine the evolution of the thermochemical state of the interstellar gas subject to pressure fluctuations. At the typical pressure of the interstellar medium the thermal balance of the neutral gas results in cold clouds, warm neutral medium, or a combination of the two (the two phase ISM). Pressure fluctuations destroy the thermal equilibrium and the resulting evolution is sensitive to the amplitude and frequency of the fluctuation. For periodic fluctuations we calculate the work done on the gas in a cyclic trajectory and determine its dependence on frequency. In particular, there are critical values of the amplitude and frequency that result in large trajectories in the phase diagram and maximize the average rate at wich mechanical energy is deposited in the gas.
