DISSOCIATION DYNAMICS OF CH4+ CORE ION IN THE (2)A(1) STATE

Threshold-photoelectron photoion coincidence (TPEPICO) spectra of CH4 have been observed with synchrotron radiation at the excitation to the (2)A(1) (nu(1)=0-3) ionic states as well as to the 4pt(2) Rydberg (nu (1)=0-4) states. In all the TPEPICO spectra observed, the CH3+ band sh ape was almost rectangular, which suggests that the translational and internal energy distributions of CH3+ are very narrow. The total kinet ic energy releases (KERs) have been estimated from the CH3+ band shape . As a result, it was found that the CH3+ species were in an electroni cally excited state. There was a narrow distribution of the total KERs and similarity in the TPEPICO CH3+ band shapes between the spectra at the (2)A(1) ionic state and the 4pt(2) Rydberg state excitations, whi ch led to the conclusion that the Rydberg electron is just a spectator and the dissociation of the core ion plays an important role in disso ciation through the 4pt(2), Rydberg state. Similar results have also b een obtained for CH2+ and CH+ productions. However, on the other hand, an H+ fragment has been observed only at the (2)A(1) state excitation . It showed a band with a long tail in the slower flight time region. The total average KERs and the decay rates have been estimated from ba nd shape simulation. From these results, it has been found that a diss ociation limit of the H+ ion exists just below the (2)A(1) ionic state . The dissociation mechanisms through the 4pt(2), Rydberg state have b een discussed in detail in comparison with those of the (2)A(1) ionic state.