Nitrobenzene as a material for the fast-respond degenerate four-wave mixing

We have revealed a possibility of using nitrobenzene (NB) as a promising for time-resolving degenerate four-wave mixing (DFWM). The DFWM efficiency versus time delay between the probe and pump beams was revealed. The four time-retarded maxima of the DFWM are caused by specific electron-vibration interactions in the NB. An essential contribution of acoustical vibrations is demonstrated. Molecular dynamics geometry optimisation of the NB molecule is done taking into account intermolecular interactions. Superposition of all possible molecular conformations with appropriate weighting factors and higher-order intermolecular multiple interactions is considered. The observed DFWM behavior is explained within the framework of ab inito quantum chemical calculations with inclusion of excited configuration interaction (CI) states. We considered both harmonic as well anharmonic electron-vibration interactions. The average lifetime of MO levels contributing to the third-order nonlinear and time kinetics of the observed DFWM dependences is estimated. Advantages and drawbacks of the prosposed method are discussed. (C) 2001 Elsevier Science B.V. All rights reserved.