Jahn-Teller effect in tetrahedral symmetry:: Large-amplitude tunneling motion and rovibronic structure of CH4+ and CD4+

The energy level structures of the ground vibronic states of (CH4+)-C-12, (CH4+)-C-13, and (CD4+)-C-12 have been measured by pulsed-field-ionization zero-kinetic-energy photoelectron spectroscopy. The nuclear spin symmetries of the tunneling-rotational levels have been determined in double-resonance experiments via selected rotational levels of the v(3)=1 and v(3)=2 vibrational levels of the X (1)A(1) ground state of CH4. The energy level structures of (CH4+)-C-12, (CH4+)-C-13, and (CD4+)-C-12 have been analyzed with an effective tunneling-rotational Hamiltonian. The analysis together with a group theoretical treatment of the T circle times(e+t(2)) Jahn-Teller effect in the T-d(M) group prove that the equilibrium geometry of (CH4+)-C-12, (CH4+)-C-13, and (CD4+)-C-12 has C-2v symmetry and characterize the pseudorotational dynamics in these fluxional cations. The tunneling behavior is discussed in terms of the relevant properties of the potential energy surface, some of which have been recalculated at the CCSD(T)/cc-pVTZ level of ab initio theory. (c) 2007 American Institute of Physics.