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We theoretically investigate the creation of the rotational wave packet in molecular ions upon the strong-field ionization of diatomic molecules by a femtosecond laser pulse. The rotational excitation of molecular cation is ascribed to the dependence of the strong-field ionization probability on the orientation angle of the molecular axis with respect to the laser polarization direction. By extending the molecular strong-field approximation theory, we calculate the rovibrational state distribution of the ground electronic X 1 Σ + state of NO+ after the ionization of NO in the electronic ground X 2 Π 1 / 2 state. We also show that the extent of the rotational excitation of NO+ is enhanced by the stimulated impulsive Raman processes both in neutral NO and in NO+ cation. The resultant time evolution of the rotational wave packet of NO+ is in good agreement with the delay dependent NO2+ yield recorded experimentally in our previous pump–probe study. [ABSTRACT FROM AUTHOR]

We examine rotational wave packet dynamics of an asymmetric top, H 2 O, by calculating the time-dependent expectation values of the squared directional cosines with respect to three molecular a , b and c axes. From comparison between the Fourier transform spectra of these expectation values and that of the pump-probe delay dependent H 2 O + yield recorded in our previous study (Kikuchi et al., 2023), we reveal that electrons are mainly emitted from the highest-occupied 1b 1 orbital but are also emitted from lower-lying 3a 1 orbital in the ionization of H 2 O in an intense laser field. [Display omitted] • Ionization of H 2 O induced by an intense laser pulse is examined. • Rotational wave packet of asymmetric top H 2 O is created by a femtosecond laser pulse. • Fourier spectra of expectation values of squared directional cosines are calculated. • Electron emission from the highest occupied and lower-lying orbitals is revealed. [ABSTRACT FROM AUTHOR]