Nonperturbative time-dependent density-functional theory of ionization and harmonic generation in OCS and CS<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mrow/><mml:mn>2</mml:mn></mml:msub></mml:math>molecules with ultrashort intense laser pulses: Intensity and orientational effects

Abstract

Molecular high-order harmonic generation (MHOHG) and molecular orbital ionization rates are calculated for the nonsymmetric OCS and symmetric CS${}_{2}$ molecules using numerical solutions of Kohn-Sham (KS) equations of time-dependent density functional theory in the nonlinear nonperturbative regime of laser-molecule interactions for different laser-molecule orientations and intensities. It is found that the ionization of inner-shell KS molecular orbitals contributes significantly to the ionization and MHOHG processes for intensities I \ensuremath{\ge} 3.5 \ifmmode\times\else\texttimes\fi{} 10${}^{14}$ W/cm${}^{2}$. Ionization rate maxima correspond to the alignment of maximum KS orbital densities with the laser pulse polarization instead of orbital ionization potentials. Furthermore, degeneracies of orbitals are removed as a function of laser-molecule angle, thus affecting ionization rates, the MHOHG spectra, and their polarizations, the latter allowing for identifying inner-orbital ionization.