Quantum model simulations of symmetry breaking and control of bond selective dissociation of FHF- using IR+UV laser pulses.

Symmetry breaking and control of bond selective dissociation can be achieved by means of ultrashort few-cycle-infrared (IR) and ultraviolet (UV) laser pulses. The mechanism is demonstrated for the oriented model system, FHF-, by nuclear wave packets which are propagated on two-dimensional potential energy surfaces calculated at the QCISD/d-aug-cc-pVTZ level of theory. The IR laser pulse is optimized to drive the wave packet coherently along alternate bonds. Next, a well-timed ultrashort UV laser pulse excites the wave packet, via photodetachment of the negative bihalide anion, to the bond selective domain of the neutral surface close to the transition state. The excited wave packet is then biased to evolve along the pre-excited bond toward the target product channel, rather than bifurcating in equal amounts. Comparison of the vibrational frequencies obtained within our model with harmonic and experimental frequencies indicates substantial anharmonicities and mode couplings which impose restrictions on the mechanism in the domain of ultrashort laser fields. Extended applications of the method to randomly oriented or to asymmetric systems XHY- are also discussed, implying the control of product directionality and competing bond-breaking.