Numerical modeling of the process of formation of gas bubbles during initiation of the microwave discharge in liquid n-heptane at atmospheric pressure has been performed. The developed model has an axial symmetry. The model is based on joint solution of the Maxwell equations, Navier-Stokes equation, heat equation, continuity equations for electrons (written in the ambipolar diffusion approximation) and the n-heptane concentration (including its thermal decomposition and dissociation by electron impact) and the Boltzmann equation for free electrons of the plasma. The calculations allowed to describe the dynamics of the formation of gas bubbles in the liquid, to evaluate the role of electron impact in the decomposition of n-heptane, and to estimate the characteristic times of various processes in the system. The results of new experiments are compared with the simulation results. On the basis of this comparison one could explain the presence in the spectra of the discharge only bands of C-2.