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

We have revealed a possibility of using nitrobenzene (NB) as a promising fo r time-resolving degenerate four-wave mixing (DFWM). The DFWM efficiency ve rsus time delay between the probe and pump beams was revealed. The four tim e-retarded maxima of the DFWM are caused by specific electron-vibration int eractions in the NB. An essential contribution of acoustical vibrations is demonstrated. Molecular dynamics geometry optimisation of the NB molecule i s done taking into account intermolecular interactions. Superposition of al l possible molecular conformations with appropriate weighting factors and h igher-order intermolecular multiple interactions is considered. The observe d DFWM behavior is explained within the framework of ab inito quantum chemi cal calculations with inclusion of excited configuration interaction (CI) s tates. We considered both harmonic as well anharmonic electron-vibration in teractions. The average lifetime of MO levels contributing to the third-ord er nonlinear and time kinetics of the observed DFWM dependences is estimate d. Advantages and drawbacks of the prosposed method are discussed. (C) 2001 Elsevier Science B.V. All rights reserved.