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) ov er tilde E-2/(B) over tilde B-2(2) interacting electronic manifold of the c orresponding cation (C3H4+) is theoretically calculated and compared with t he most recent high resolution He I excited experimental recording of Baltz er et al. [Chem. Phys. 196, 551 (1995)]. A model diabatic Hamiltonian withi n the linear vibronic coupling scheme and ab initio calculated coupling par ameters 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 el ectronic 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 elect ronic manifold with the (B) over tilde(2)B(2) electronic state via degenera te 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].