Knowledge Bank

There has been long-term interest in developing methods to align or orient molecules to study steric effects in collision. Recently, friedrich and Herschbach and Loesch and Remsheid have explored the use of large static electric fields to ""brute-force"" orient linear molecular. For molecules exicited to regions of high vibrational state density where intramolecular vibrational energy redistribution (IVR) occurs, additional complications need to be considered when designed experiments which require that the excited molecules be aligned or oriented. We have recently shows, for example that a molecule excited to a single molecular eigenstate in regions of high state density is no longer defleted by inhomogeneous fields when the mean spacing between vibrational levels in on the order of the mean molecule-field interaction strength. The present talk explores theoretically the consequenece of using ""brute force"" orientation techniques for molecules excited to regions where IVR is important. The molecule HCCF is chose as a model system for this study since the anharmonie forde field is well characterized, allowing a realistic description of the energy levels and couplings in the high-density-of state regime. Our result show rapid dephasing of the orientation, even in the absence of any explicit Coriolis couplings of the vibration and rotational degrees of freedom. We find that the effect is induced by nonadiabatic couplings of the pendular ladders built upon different vibrational state. The nonadiabatic couplings requirs that, the rotational constants or dipole moments differ between vibrational states in order that the pendular wavefunctions be nonorthogonal. The present results suggest that the orientation lifetime will be similar to the IVR lifetime when the ""brute-fore"" approach is used to orient molecules in regions of high vibrational state density.