Laser control scheme for state-selective ultrafast vibrational excitation of the water-d molecule

SELECTIVE EXCITATION OF HIGH VIBRATIONAL STATES OF HYDROGEN FLUORIDE IN A THERMAL ENVIRONMENT BY ULTRAFAST INFRARED LASER PULSES

The selective excitation of the high ground vibrational state of rotationless HF in an unobserved quasi-resonant thermal environment under the control of a single pulse and pulse train is studied using the reduced density matrix theory. It is shown that the pulse train can enhance the population transfer probability. The numerical results reveal that the vibrational relaxation process is affected by the distribution of the environment frequency and the molecule–environment coupling intensity. The effects of the molecule–environment coupling parameter and the overlapping pulses on the population of the target state of HF are also discussed.

Theoretical Study of the Reaction of H Atoms with Vibrationally Highly Excited HF Molecules

Vibrationally highly excited molecules react extremely fast with atoms and probably with radicals. The phenomenon can be utilized for selectively enhancing the rate of reactions of specific bonds. On the basis of quasiclassical trajectory calculations, the paper analyzes mechanistic details of a prototype reaction, H + HF(v). At vibrational quantum numbers v above 2, the reaction exhibits capture-type behavior, that is, the reactive cross section diverges as the relative translational energy of the partners decreases, both for the abstraction and for the exchange channel. The mechanism of the reaction for both channels is different at low and at high translational energy. At low vibrational energy, the reaction is activated, which is switched to capture-type at high excitation. The reason is an attractive potential that acts on the attacking H atom when the HF molecule is stretched. In contrast to the 6-SEC potential surface of Mielke et al., the switch cannot be observed on the Stark-Werner potential surface, due to a small artificial barrier at high H-HF separation, preventing the reactants from obeying the attractive potential and also proving the importance of the latter. The exchange reaction can be observed even when the total energy available for the partners is below the exchange barrier, because at low translational energies the product F atom of a successful abstraction step can re-abstract that H atom from the intermediate product H2 molecule that was originally the attacker.

Active control of the dynamics of atoms and molecules

There has been much progress in the control of chemical reactions since methods of active control were first proposed by Brumer & Shapiro and by Tannor & Rice ten years ago. This chapter reviews both theoretical and experimental advances in the field. Control schemes based on quantum mechanical interference between competing paths and the manipulation of wave packets with tailored laser pulses are discussed. The theory of optimal control, the limitations of control theory applied to many-body dynamics, and the effects of constraints on the trajectory of the controlled observable are presented. Experimental progress in controlling the population of specific quantum states, in manipulating the dynamics of bound wave packets, and in the control of chemical reactions are reviewed, and current problems in the field are summarized.