Laser-Induced Electronic and Nuclear Coherent Motions in Chiral Aromatic Molecules

Abstract

The results of theoretical studies on laser-induced electronic and nuclear motions of chiral aromatic molecules are reviewed. The control schemes for π-electron rotation (ring current) and nonadiabatically coupled molecular vibration in chiral aromatic molecules by means of ultrashort linearly polarized laser pulses are presented. Ansa (planar-chiral) aromatic molecules with a six-membered ring, which are pyrazine derivatives, are adopted as model systems. We provide the pulse-design scheme to induce π-electron rotation and show that the rotation direction, clockwise or counterclockwise, can be controlled by the polarization direction of the incident linearly polarized laser pulse. The linearly polarized laser pulse creates a linear combination of quasi-degenerate excited states. Then the results of nuclear wave-packet simulation taking into account the nonadiabatic coupling between optically induced π-electron rotation and molecular vibration are compared to those obtained within the Born-Oppenheimer approximation. Strong dependence of the vibrational amplitudes on rotation direction of π electrons as a consequence of nonadiabatic coupling was found. Vibrational wave packets on the potential surfaces in the two electronic states are produced, and they interfere with each other, constructively or destructively. This suggests that attosecond π-electron rotation can be identified by spectroscopic detection of femtosecond molecular vibrations. Photon polarization-dependent nonadiabatic coupling effects of coherently excited quasi-degenerate electronic states are also explained by an analytical treatment.