PREPARATION OF IONS IN SELECTED ROTATIONAL STATES BY DELAYED PULSED-FIELD IONIZATION

A novel method of preparing ions in selected rovibronic states is presented. It is based on pulsed field ionization of long-lived high-n Rydberg states lying just below the different rovibronic energy levels of the ion. The potential of the method is illustrated with the example of hydrogen: A clean population of H-2+ ions is prepared in the X2SIGMA(g)+ (upsilon+ = 2, N+ = 0, 1, 2, 3) states. The method ought to be applicable to the preparation of a wide range of small molecular ions in selected rotational states and opens new possibilities in the study of state-to-state ion-molecule reactions.