Investigating the Photodetachment Spectrum of Al 3 $_3$ O 3 - $_3^-$ : A Theoretical Approach

In this study, vibronic coupling in the first six low-lying electronic states ( $\tilde{X}$ , $\tilde{A}$ , $\tilde{B}$ , $\tilde{C}$ , $\tilde{D}$ , and $\tilde{E}$ ) of the book-type isomer of Al ${}_3$ O ${}_3$ is investigated using both adiabatic and nonadiabatic approaches. A $6\times 6$ vibronic Hamiltonian is formulated within a diabatic framework to perform both time-dependent (TD) and time-independent (TI) quantum dynamics simulations. In the adiabatic framework, wavepacket density plots are employed to assign vibronic lines, while in the nonadiabatic framework, population transfer dynamics and conical intersection (CI) geometries are explored to explain the observed ultrafast decay and spectral broadening. The simulated 266 nm photoelectron spectrum is found to reproduce the two experimental bands observed up to 4.0 eV, and four additional features at higher electron binding energies (∼6.0-7.0 eV) are predicted. From these results, insight into the nonadiabatic mechanisms governing the detachment dynamics of Al ${}_3$ O ${}_3^{-}$ is gained, and a comprehensive theoretical description of its electronic states is provided.