title: Jahn-Teller effect in the methane cation: Rovibronic structure and the geometric phase.
abstract: The rovibronic structure in the photoelectron spectrum of CH4 has been assigned in infrared-vacuum ultraviolet double-resonance experiments and analyzed using an effective tunneling-rotation Hamiltonian. Comparison of theoretical and experimental level structures of CH4+ reveals the effect of the geometric phase and establishes that at low energies, the structure and dynamics are governed by a large-amplitude tunneling motion connecting equivalent minima of C(2v) geometry. The rotationless ground state of CH4+ is a tunneling doublet of triply degenerate levels and the lowest level has rovibronic symmetry F2. The adiabatic ionization energy of CH4 is 101753.0(15) cm(-1).
authors.affiliation: Laboratorium für Physikalische Chemie, ETH Zürich, CH-8093 Zurich, Switzerland.
authors.forename: H J
authors.initials: HJ
authors.lastname: Wörner
authors.forename: R
authors.initials: R
authors.lastname: van der Veen
authors.forename: F
authors.initials: F
authors.lastname: Merkt