MOLECULAR-ORIENTATION CONTROL FOR (JKMJ)-SELECTED CH3I VIA INFLUENCE OF ELECTRIC-FIELD ON NUCLEAR HYPERFINE COUPLING

Using the polarized laser photofragment photoionization technique, measurements have been made of the degree of orientation of CH3I in \JKMJ〉 = |111〉 and |222〉 parent rotational states under the influence of homogeneous electric fields (E) from 0 to 1.0 kV cm -1. From a series of experiments on hexapole-oriented molecules in weak fields, it has been found that the original degree of orientation of the symmetric-top molecules can be recovered after they pass through a homogeneous weak-field region provided that the field strength therein exceeds some minimum value (E≳0.3 V cm-1), sufficient to maintain an orientation axis. Even though the |JKMJ〉 parent states have "relaxed" via hyperfine coupling to an ensemble of |FJKIM F〉 states, when the molecules later pass into a strong E field, the ensemble is restored to its original degree of orientation. Another set of experiments in moderate to strong fields provided "saturation curves," i.e., the dependence of the degree of orientation upon E. The results show that quite high field strengths (>0.5 kV cm-1) are required to ensure total decoupling of J from I and thus recovery of the full orientation. From these experiments it is now clear that one can control the degree of molecular orientation by placing the state-selected molecules in a know E field. © 1990 American Institute of Physics.