Influence of pulse width, laser wavelength and laser intensity on state populations of a NaI molecule driven by a pump-probe pulse was studied via time-dependent wave packet approach.Wave packet moves periodically with roundtrip time 1 000 fs.Wave packet bifurcates in crossing region firstly at delay time 200 fs, which affects state populations.Excitation probability increases and dissociation probability decreases with increasing pulse width.Excitation probability approaches the maximum at resonance pump wavelength 318 nm.Dissociation probability decreases with increasing pump wavelength.As pump intensity increases, excitation probability increases while dissociation probability does not change.Probe wavelength and probe intensity do not affect state populations.Wave packet motion and selective distribution of state populations can be achieved by adjusting laser parameters.It provides bases for realizing light manipulation of molecules experimentally.

Autler-Townes (AT) splitting in photoelectron spectra of four-level ladder K₂ molecule driven by three laser pulses is investigated with time-dependent wave packet approach. Dependence of AT splitting on second laser pulse is studied. Photoelectron spectra show triple splitting with symmetric profiles in resonance, while triple splitting with asymmetric profiles is transformed into double splitting gradually in nonresnance. Three peaks shift to lower energy differently as laser wavelength increases. Splitting between two sideband peaks does not vary with laser wavelength, but increases with increasing laser intensity. These results are of importance for molecular spectroscopy. It stimulates theoretical studies from first principles and provides basis for realizing optical control of molecules.