title: Rotationally resolved photoelectron spectroscopic study of the Jahn-Teller effect in allene.
abstract: The pulsed-field-ionization zero-kinetic-energy photoelectron spectra of allene (C(3)H(4)) and perdeuterated allene have been recorded from the first adiabatic ionization energy up to 2200 cm(-1) of internal energy in the cations at a resolution sufficient to observe the full rotational structure. The intensity distributions in the spectra are dominated by vibrational progressions in the torsional mode, which were analyzed in the realm of a two-dimensional model of the Emultiply sign in circle(b(1) plus sign in circleb(2)) Jahn-Teller effect in the allene cation [C. Woywod and W. Domcke, Chem. Phys. 162, 349 (1992)]. Whereas the rotational structure of the transitions to the lowest torsional levels (0(0) and 4(1)) are regular and can be qualitatively analyzed in terms of a simple orbital ionization model, the rotational structure of the spectra of the 4(2) and 4(3) levels are strongly perturbed. The photoelectron spectrum of C(3)H(4) also reveals several weak vibrational bands in the immediate vicinity of these levels that are indicative of (ro)vibronic perturbations. A slight broadening of the transitions to the 4(1) levels compared to that of the vibronic ground state and the increase of the number of sharp features in the rotational structure of the spectrum of the 4(2) level point at the importance of large-amplitude motions not considered in previous treatments of the Jahn-Teller effect in the allene cation.
authors.affiliation: Laboratorium fur Physikalische Chemie, ETH Zurich, CH-8092 Zurich, Switzerland.
authors.forename: A M
authors.initials: AM
authors.lastname: Schulenburg
authors.forename: F
authors.initials: F
authors.lastname: Merkt