Localized Vibration-Formation by Driving Raman Active Molecular Vibrations

The study on local modes as a molecule's eigen-vibration is still an attracting topic [1,2]. However, a new trend becomes more popular: people are more interested in the vibration properties of molecules under interactions with external laser fields for practical usages such as bond-selective photodesorption [3, 4] and vibrationally mediated dissociation [ 5 7 ] . We have already studied the possibility to creat localized vibrations by using lasers [8]. Using quantum mechanics we have shown that a set of normal mode vibrational states can be mixed properly into a local mode [8], but we did not treat the molecular vibrational motion directly. In the present paper we consider concretely the couplings between lasers and molecular vibrations in order to solve the molecular vibrational motion problem. Taking YX2 type molecules as an example, we deal with the vibrational motion directly in the classical picture of forced oscillations and illustrate how a localized vibration can be formed through stimulating a set of Raman-active normal modes by lasers. In the classical picture, when a molecule is driven by lasers, the molecule may vibrate as forced oscillations. Here we analyze YX 2 (massY > m a s s x ) type molecules to explain our idea. We make the following assumptions: