Femtosecond two-photon photoassociation of hot magnesium atoms: A quantum dynamical study using thermal random phase wavefunctions (original) (raw)

2013, The Journal of Chemical Physics

Two-photon photoassociation of hot magnesium atoms by femtosecond laser pulses is studied from first principles, combining ab initio quantum chemistry and molecular quantum dynamics. This theoretical framework allows for rationalizing the generation of molecular rovibrational coherence from thermally hot atoms [L. Rybak et al., Phys. Rev. Lett. 107 , 273001 (2011), arXiv:1107]. The coupled cluster and multi-reference configuration interaction frameworks are used to calculate the relevant potential energy curves, one-photon and two-photon transition matrix elements, dynamical Stark shifts, as well as spin-orbit couplings and nonadiabatic radial couplings. Random phase thermal wavefunctions are employed to model the thermal ensemble of hot colliding atoms. Comparing three different choices of random phase thermal wavefunctions, the free propagation approach is found to have the fastest initial convergence for the photoassociation yield. When further refinement is required the eigenvalue approach is superior. The interaction of the colliding atoms with two time-delayed femtosecond laser pulses is modeled non-perturbatively to account for strong-field effects observed in the experiment. Good agreement between experimental and theoretical results is obtained. 2 J P 2 J P g J where P g J = Tr[(e −βĤ J g ) 2 ]/Z 2 J , andĤ J