INTERNAL-ROTATION OF METHYL-GROUP IN O-TOLUIDINE AND M-TOLUIDINE CATIONS AS STUDIED BY PULSED-FIELD IONIZATION ZERO KINETIC-ENERGY SPECTROSCOPY

Internal rotational levels of the methyl group in o- and m-toluidine c ations have been observed by pulsed field ionization-zero kinetic ener gy photoelectron spectroscopy. Level energies and transition intensiti es were reproduced by a one-dimensional rotor model with a free-rotor basis set, and the potential curves of the internal rotation in the ca tions have been determined. Analysis for m-toluidine shows a drastic i ncrease of the barrier height for internal rotational motion from the neutral to the corresponding cation. On the other hand, the barrier in o-toluidine slightly decreases by ionization. The mechanism of the ch ange in barrier height will be discussed in terms of geometrical and e lectrical change by ionization. It is suggested that the drastic chang e of internal rotational motion is mainly determined by the electronic structure. (C) 1996 American Institute of Physics.