Rovibronic analysis of the Jahn-Teller effect in CH2D2+ at low energies

The Jahn-Teller effect in the ground state of CH2D2+ has been studied by pulsed-field-ionization zero-kinetic-energy photoelectron spectroscopy. The lowest three bands have been assigned to the three isomers CHlHlDsDs+, CHlHsDlDs+, and CHsHsDlDl+, in which the deuterium atoms are attached to the central carbon atom by two short bonds, one short and one long bond, and two long bonds, respectively, and which have different zero-point vibrational energies. Whereas CHlHlDsDs+ and CHsHsDlDl+ can each be described by a single structure with C-2 upsilon symmetry, CHlHsDlDs+ corresponds to four equivalent C-1 structures that interconvert by tunneling. The rotational structure of these three bands is compared with predictions made on the basis of a tunneling Hamiltonian combined with a rotational Hamiltonian that incorporates the effects of the large-amplitude tunneling motion. The zero-point energies of CHlHsDlDs+ and CHsHsDlDl+ relative to that of CHlHlDsDs+ are Delta = 123.6(5) cm(-1) and Delta' = 243.2(5) cm(-1), respectively, and the tunneling matrix element sigma coupling the four C-2 upsilon equilibrium structures of CHlHsDlDs+ is -1.7(4) cm(-1). (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3157210]