The effect of nonlinear interaction of molecules on the intensity of radiation emitted by them at transitions between vibrational levels is studied theoretically. For this purpose, the solution of a nonlinear Schrodinger equation describing the state of interacting diatomic molecules is analyzed. It is shown that in the case that the kinetic degree of freedom of molecules can be considered as a heat bath, the population of vibrational levels is close to the Boltzmann distribution in a broad range of temperatures. However, when the energy of heat motion becomes less than some critical limit, rather fast destruction of excited levels should occur. Such a behavior of the population density of quantum states should result (as the temperature of a molecular ensemble drops down below some limit) in practically complete disappearance of spontaneous and stimulated emission.