The influence of ultrashort excitations on the vibrational dynamics in a diatomic molecule

The problem of vibrational wave packet dynamics in the system of two electr onic states of a diatomic molecule, where the states are coupled by infinit ely short light pulses, is solved. The electronic states were modeled by sh ifted harmonic oscillators with different frequencies. Exact expressions fo r the probability densities of the wave packets in the ground and excited s tates were derived. The spatial, spectral, and temporal characteristics of the wave packets, namely, the range of motion, spatial width, mean energy, spectral width (the mean number of vibrational states in a wave packet), an d the autocorrelation function, were calculated as functions of the molecul ar parameters (the frequency ratio and the distance between the potential m inima) and of the delay time between the light pulses. The possibility of c ontrolling the mean energy and spectral width of the wave packets in the gr ound electronic state by varying the delay time is considered. It was shown that "squeezed" wave packets can be prepared in the ground electronic stat e if the upper electronic state is shallow.