Diatomic molecular vibrations in a strong infrared laser field: an analytic treatment of the laser-dressed Morse potential

Diatomic molecules driven by strong laser pulses show a rich variety of fundamentally important processes, depending on how the laser pulse parameters are related to the diatomic's properties. Although the theoretical framework for molecules interacting with laser fields is well established, analytic methods are rare and approximate in the strong-field domain, while most of the numerical methods have heavily increasing cost for infra-red (IR) wavelength [1,2].

In this contribution we present a general mathematical method to treat a Morse potential in the presence of a strong IR excitation. The interaction term of the Hamiltonian includes the permanent and laser-induced dipole moment of the diatomic (verified by DFT calculation), therefore, our model can be applied to both homo- and heteronuclear diatomics. As a possible use we apply our procedure to H₂ and LiH and we show how an IR laser field in the intensity range of 10¹²-10¹³ W/cm² noticeably shifts the vibrational levels and the equilibrium internuclear distance of the molecules. According to our results, the dipole gradient and the polarizability gradient are the essential molecular parameters in these effects. We give the exact analytic energy eigenvalues of the molecular vibration utilizing the Kramers-Henneberger frame [3].

[1] A. Palacios, J. L. Sanz-Vicario, and F. Martín, Theoretical methods for attosecond electron and nuclear dynamics: applications to the H₂ molecule, Journal of Physics B: Atomic, Molecular and Optical Physics 48, 242001 (2015).

[2] B. Molnár B, P. Földi, M. G. Benedict and F. Bartha, Time evolution in the Morse potential using supersymmetry: Dissociation of the NO molecule Europhysics Letters 61, 445–451 (2003)

[3] S. Varró, Sz. Hack, G. Paragi, P. Földi, F. Barna and A. Czirják, Diatomic molecule in a strong infrared laser field: level-shift and bond-length change due to laser-dressed Morse potential (in preparation)