We compare strong-field ionization probabilities of N2 and F2 molecules using time-dependent density functional theory calculations. Accurate nuclear potentials and ground vibrational wave functions are incorporated into our study. For both molecules, the effect of molecular vibration is small, while that of the molecular orientation is significant. When compared to the ionization probability of a molecule at the equilibrium geometry, we estimate the effect of the ground state vibration to be within 3% for N2 and within 6% for F2 in the intensity range from 1 to 5×1014 W/cm2. The molecular-orientation-dependent ionization probabilities for both molecules at various intensities are presented. They are strongly dependent on the laser intensity, and the anisotropy diminishes when the laser intensity is high. For laser intensities of 1.6 and 2.2×1014 W/cm2 we find ionization probability ratios of 5.9 and 4.3, respectively, for the parallel versus perpendicular orientation of N2. This is reasonably consistent with experimental measurements. For randomly oriented molecules, the ratio of the probabilities for N2 and F2 increases from about 1 at 1014 W/cm2 to 2 at 4×1014 W/cm2, which agrees well with experimental results.
|Physical Review A - Atomic, Molecular, and Optical Physics
|Published - Jan 24 2011