Theoretical investigation of Jahn-Teller and pseudo-Jahn-Teller coupling effects on the photoelectron spectrum of allene

The valence photoelectron spectrum of allene (C3H4) pertinent to the (A) over tilde E-2/(B) over tilde B-2(2) interacting electronic manifold of the corresponding cation (C3H4+) is theoretically calculated and compared with the most recent high resolution He I excited experimental recording of Baltzer et al. [Chem. Phys. 196, 551 (1995)]. A model diabatic Hamiltonian within the linear vibronic coupling scheme and ab initio calculated coupling parameters are employed in our investigations. While the resolved vibrational progressions in the photoelectron band at low energies can be attributed to the E circle times B Jahn-Teller activity within the (A) over tilde E-2 electronic manifold, the diffuse structure in the photoelectron band at high energies is found to emerge from the mixing of the (A) over tilde E-2 electronic manifold with the (B) over tilde(2)B(2) electronic state via degenerate vibrational modes. The latter demonstrates the importance of the pseudo-Jahn-Teller type of interactions in the photoelectron spectrum of allene. (C) 1999 American Institute of Physics. [S0021-9606(99)00347-5].