A semiclassical coupled dressed-quasimolecular-states (DQMS) approach is presented for nonperturbative treatment of multichannel charge-transfer reactions at low collision velocities and high laser intensities, incorporating the implementation of the generalized Van Vleck (GVV) nearly degenerate perturbation theory. The GVV technique allows block partitioning of the infinite-dimensional Floquet Hamiltonian into a finite-dimensional model DQMS space, and thereby reduces greatly the number of effective coupled channels. Further, the GVV-Floquet basis allows minimization of the (usually large in amplitude) field-induced nonadiabatic radial couplings without the need to explicitly construct the transformation between the adiabatic and diabatic DQMS basis. This yields a new set of coupled GVV-DQMS equations (neither adiabatic nor diabatic) which are particularly convenient for multichannel calculations. The method is applied to the study of the laser-assisted charge-transfer process: ${\mathrm{Li}}^{3+}$+H(1s)+ħω→${\mathrm{Li}}^{2+}$(n= 3)+${\mathrm{H}}^{+}$, using 2-, 5-, and 15- GVV-DQMS basis. It is found that while the 5-state results agree well with the 15-state calculations even up to very high intensities for the (LiH${)}^{3+}$ system, the 2-state basis is inadequate at high-intensity and lower-wavelength regimes. Detailed results and nonlinear dynamical features are presented for the process at small impact velocity ${10}^7$ cm/s and strong laser fields with intensity ranging from 1 to 100 TW/${\mathrm{cm}}^2$ and wavelengths from 1500 to 3000 Å.

• Received 4 March 1985

DOI:https://doi.org/10.1103/PhysRevA.32.122