Quantum model of dynamic Stark‐induced degenerate vibronic state by two nonresonant shift‐up lasers for π‐electron angular momentum generation

Abstract

AbstractA theoretical scenario for the generation of coherent π‐electron angular momentum in a low‐symmetry aromatic molecule using two nonresonant shift‐up lasers is presented. The effects of vibrational modes on coherent π‐electron angular momentum are considered in the adiabatic approximation. In this scenario, two electronic excited states are irradiated with two linearly polarized nonresonant lasers. This causes a consistent up‐shift in the vibronic energy levels of each electronically excited state toward higher energy as a result of the dynamic Stark effect. For the weak coupling case of the electronic‐vibrational interactions, the lowest vibronic states in the two electronic excited states are designed to be degenerate by varying the parameters (frequency and intensity) of each laser. The resultant degenerate state, called the dynamic Stark‐induced degenerate vibronic state (DSIDVS), is the origin of the coherent π‐electron angular momentum generation. An optimal laser parameter set is determined under conditions in which the lowest two vibronic states form the DSIDVS. The DSIDVS was formulated by the method of Laplace transformations. An analytical expression for the coherent π‐electron angular momentum was derived in the displaced harmonic oscillator model. We examined the dependence of the time‐averaged z‐component of the coherent angular momentum on the ratio of the two detunings and potential displacements of toluene, a typical low‐symmetry aromatic ring molecule, which belongs to the weak coupling case and is adopted to demonstrate the theoretical scenario. The inclusion of potential displacements in the angular momentum generation was found to reduce the value of by half, compared with that in the frozen nuclear approximation.