Quasistationary resonances induced by intense infrared fields in HD+and their decay

Abstract

The nature of a few low-lying laser-induced resonances of HD${}^{+}$ along with their linewidths due to dissociation, has been investigated in the intensity range of (1--6) $\ifmmode\times\else\texttimes\fi{}{10}^{13}\mathrm{W}/{\mathrm{cm}}^{2}$ for three different laser frequencies. In the length gauge representation of the interaction Hamiltonian used by us, these resonances for the lower intensities are basically the vibrational states of the unperturbed molecule, shifted and broadened by radiative interactions. At higher intensities the resonances are obtained as quasistationary states on different adiabatic potentials. They are formed by the mixing of various unperturbed vibrational states by multiphoton interactions. In this mixing, the proportion of vibrational states further away from the resonance energy increases with the increase in intensity. At high enough intensities, signature of dissociation through a nonresonant intermediate vibrational transition to the $v=6$ and $v=7$ state is observed for a laser frequency of 12 500 cm${}^{\ensuremath{-}1}$. The width of the lowest resonance increases sharply with intensity, while its shift from the $v=0$ state increases only linearly with intensity. The branching ratios to different photon absorption channels change with intensity and they can be interpreted using the adiabatic potential curves. For a frequency of 2000 cm${}^{\ensuremath{-}1}$, which is close to the frequency of $v=0$ to $v=1$ transition, the resonances arise from the mixing of various vibrational levels through stepwise transitions, resulting in a dissociation linewidth larger compared to that obtained for higher frequencies.