Twisted Angle of Allene Cation From Analysis of High-Resolution Photoelectron Spectrum

1 Introduction Allene is a prototype molecule with D2d molecular point group. In its ground state, the two planes scanned by the two CH2 groups are perpendicular, corresponding to two normal π molecular orbitals, i. e. the twisted angle of the two CH2 groups is 90°. It is of special interest to investigate the change of the twisted angle when allene is ionized. As well known, the individual bands of photoelectron （PE） spectra reflect the corresponding states of the cation studied. Several papers have been published to discuss the twisted angles of allene cation in its ground state, but the values of the twisted angle obtained by different methods are not in good agreement. Recently, high-resolution molecular