  The amplitude and probability of quantum transitions are represented as a
path integrals in energy state space of the investigated multi-level quantum
system. Using this approach we consider rotational dynamics of nitrogen
molecules $^{14}N_{2}$ and $^{15}N_{2}$ which interact with a sequence of
ultrashort laser pulses. Our computer simulations indicate the complex
dependency of the high rotation states excitation probability upon ultrashort
laser pulses sequence periods. We observe pronounced resonances, which
correspond to the results of some experiments.
